Osseointegration has been shown to be directly affected by surface roughness and bioactive coatings. This report compares bone response to hydroxyapatite coatings on differing substrate treatments.

Titanium cylinders was implanted bilaterally in the distal femora of 30 rabbits. One of three surface treatments was applied to each implant: plasma sprayed titanium surface without hydroxyapatite coating (P), plasma sprayed titanium surface with hydroxyapatite coating (PHA), and acid-etched surface with hydroxyapatite coating (CHA). Osseointegration was measured at 6 and 12 weeks, by histomorphometry of scanning electron microscopy images of histologic sections taken through the implant at three levels: diaphysis, metaphysis, and intermediate. Bone growth was measured up to 3 mm from the edge of the implant to determine changes in patterns of bone growth.

Overall, bone response was greatest in the diaphyseal sections. Mean osseointegration was significantly different between hydroxyapatite coated and non-hydroxyapatite coated implants (CHA: 74+10%, PHA: 65+12%, and P: 39+10%, p< 0.01). Both hydroxyapatite coated implants demonstrated increased bone growth closer to the implant which dropped off with increasing distance from the implant. Lower and relatively unchanging levels of bone growth were seen in non-hydroxyapatite coated implants.

Osseointegration and bone growth was higher in both hydroxyapatite coated surfaces confirming previous reports. The differences in substrates (acid etched vs. plasma sprayed titanium) did not yield a significant difference in bone growth, suggesting that the hydroxyapatite coating provided a much larger benefit. This study supports the hypothesis that enhanced osseointegration is primarily due to the bioactive coating.

A common finding in acetabular revisions is loss of medial bone stock. Using a standard cementless hemispherical component, alternatives for reconstruction include medialisation of the cup, medial particulate allograft with rim fixation on host bone, or use of a “mega-cup”. A cementless shell that has 6 mm of lateral augmentation is useful in restoring the joint centre while at the same time achieving implant stability and increasing host bone contact without loss of additional bone.

From 1991 to 2000, a total of 142 acetabular revisions were performed with the Arthropor TM DP+6 implant (Joint Medical Products/J& J/DePuy). These patients have been prospectively followed bi-annually with Harris Hip Scores and monitoring of complications and radiographic findings. Average follow-up is 5 years (range 2 to 11 years).

Implant survivorship is 100%. There have been seven re-operations: one for infection (debrided), two for femoral revision and four head/liner changes for recurrent dislocations. Dislocation incidence is 7.8%. The average Total Harris Score at 5 years is 74.3, with an average Harris Pain Score of 34.9 (out of a maximum of 44). Radiographic analysis showed frequent zone 3 radiolucent zones. Initial migration of > 2 mm with subsequent stabilisation occurred in 18%. The joint centre was restored to within 5 mm of the contralateral hip in 85% of cases.

We have found this type of implant to be efficacious in the more common acetabular revisions where the loss of bone stock is mainly medial/cavitary, with an intact posterior column and small medial segmental defects.

In this study we intend to evaluate the outcomes for patients with the Rotaglide mobile meniscal knee prosthesis implanted for osteoarthritis. All patients reviewed had this prosthesis implanted as a primary total knee arthroplasty in Crosshouse hospital.

The minimum follow up period was 5 years (range 5 to 8.2). Patients were assessed clinically by the junior author (CW) and the results were standardised using the Hospital for Specialist Surgery (HSS) knee score. Standard radiographs were taken in AP and lateral planes to assess for loosening using the Knee Society roentgenographic system. Case notes were then examined for evidence of complications in the peri and postoperative complications.

Sixty-five patients (71 knees) were reviewed. There was an excellent clinical outcome with HSS scores of 85 in 97.1% of patients. Two knees (2.9%) were revised, one for meniscal fracture and one for meniscal dislocation. Both these patients also attended for review and were making good progress. Both of these failures occurred early in our series and in a total of 312 knees to date there have been no other meniscal failures. No knees were revised for aseptic loosening and there have been no deep infections.

We feel this prosthesis offers a safe and effective treatment for osteoarthritis with a good clinical outcome at 5 years with a low level of complications.

Genetic defects causing dwarfism occur in approximately 1 in 10 000 live births. There are over 200 types. Another frequent cause of short stature is juvenile rheumatoid arthritis. Most types of dwarfism result in arthrosis of major joints resulting in significant disability. Hip replacement can offer significant improvement in quality of life, but there are inherent difficulties due to size and anatomic variations.

Short stature of less than 4 feet 10 inches was defined as dwarfism. Eight patients meeting this criterion underwent either primary or revision total hip replacement, with six being bilateral, resulting in a total of 14 hips for study (six primaries and eight revisions). The diagnoses were: two JRA, two Mucolipdosis III, one Dyastrophic Dwarfism, one Spondyloepiphyseal Dysplasia, one Thalasemia, and one Congenital Rickets. In eight hips a CT-based custom cementless femoral component was used. Average follow-up was nine years (2 – 14).

The average Total Harris Hip Score improved from 35 pre-operatively to 66 at last follow-up, with the average Harris Pain Score increasing from 10 to 31 (out of a maximum of 44). Of the six primary hips, two hips in the same patient have been revised for combined acetabular and femoral loosening. Of the eight revision hips, there have been three re-operations: one re-revised for acetabular loosening, one re-revised for late hematogenous infection and one head/liner change for recurrent dislocations.

Hip replacement in dwarfs presents a complex technical challenge, but can result in significant improvement in pain, function and quality of life. CT-base custom femoral components are recommended.

Patients with advanced osteoarthritis tend to have limited range of motion; the purpose of this in vivo anatomical study is to identify the anatomical structures responsible for limited knee movement in patients with osteoarthritis.

Forty-two quadriceps releases were performed in patients who had TKA. The releases were carried out utilising subvastus approach and just before proceeding with the knee replacement surgery. The ranges of motion were documented before and after the release using digital photography and lateral portable X-ray. No bony resection was done, and no ligament release was performed. Quadriceps excursion was also studied under fluoroscopy in six volunteers throughout the range of movement.

The quadriceps release improved the range of motion in all patients; at least 135 degrees of flexion were obtained. The improvements were more dramatic in patients who had previous surgeries. The average of improvement in knee flexion after the release was 36 degrees. The presence of osteophytes or gross deformity did not influence the degree of improvement. The fluoroscopy study has shown that the average excursion of quadriceps muscle from 0 to 145 degrees is 7 cm. The excursion per degree varies throughout the range of motion; it is more per degree near full flexion and extension than around 90 degrees of flexion.

The limited excursion of the quadriceps muscle is the main limiting factor to full knee flexion. Other pathological changes such as osteophytes, surface pathology, posterior capsule and the cruciate ligaments play very limited roles.

The aim of the study was to determine the precision of conventional versus computer-assisted techniques for positioning the acetabular component in total hip arthroplasty (THA).

Malposition of the acetabular component during THA increases the occurrence of impingement, reduces range of motion, and increases the risk of dislocation and long-term wear. To prevent malpositioned hip implants, an increasing number of computer assisted surgery systems have been described, but their accuracy is not well established.

Using a lateral approach, 150 cups were placed by 10 different surgeons in 10 identical plastic pelvis models. Only the immediate operating field was visible. Pre-operative planning was performed with a computerised tomography scan. Fifty cups were placed free hand, 50 others with the standard cup positioner, and the remaining 50 cups using computer-assisted orthopaedic surgery (Medivision). The accuracy of cup abduction and anteversion was assessed with an electromagnetic system (Fastrak™).

Using conventional techniques, free hand placement revealed a mean precision of cup anteversion and abduction of 10° [range 5.5 to 14] and 3.5° [2.5 to 5] respectively. With the cup positioner, these angles measured 8° [5 to 10.5] and 4° [3 to 5.5] respectively, and using the computer assisted method, the mean cup anteversion precision was 1.5° [1 to 2] and mean cup abduction measured 2.5° [2 to 3.5].

Computer assisted cup placement is a very accurate and reproducible technique during THA. It is clearly more precise than either of the two traditional methods of cup positioning, even for well-trained surgeons.

Absorbable cement restrictors have been in use over the last few years. They have been shown to be as effective as the standard non-absorbable cement restrictors in achieving cement pressurisation and stopping distal cement migration in in vitro studies. The aim of this study is to compare in vivo, the effectiveness of absorbable with non-absorbable cement restrictors.

One hundred and thirty-six consecutive patients who had total hip replacement performed using charnley cemented femoral prosthesis were selected and randomly divided in to two groups pre operatively. One group received Hardinge TM non-absorbable cement restrictor and the second group received Biostop TM absorbable cement restrictor. Type of the prosthesis, the surgical approach, the time from start of mixing of the cement to insertion of the cement (measure of viscosity of the cement), the cementing technique and the distance at which the cement restrictor was inserted were noted intraoperatively, the canal diameter was measured from the preoperative AP radiograph of the hip. The distance at which the cement restrictor was inserted was measured on the AP radiograph of the hip taken twenty-four hours postoperatively. All the above factors were statistically assessed as to their effect in the distal migration on cement restrictor using multiple regression analysis.

There was no statistical difference between the two types of cement restrictors (P= 0.44). Surgeon, Surgical approach, femoral canal diameter P> 0.2 cementing technique P> 0.1 and Cement viscosity P= 0.082 had no effect on the degree of distal migration of the cement.

In conclusion Biostop TM absorbable cement restrictor is as effective as Hardinge TM non-absorbable cement restrictor. We could not show any relationship between femoral canal diameter cementing technique and cement viscosity and distal cement migration which leads us to conclude that in the presence of adequate cement restriction these factors have little effect in distal migration of cement mantle.

Revision total hip arthroplasty, with retention of well fixed femoral and acetabular components and exchange of modular femoral heads and acetabular liners, is seeing increasing usage, primarily for the treatment of osteolysis or recurrent dislocations. The purpose of this study was to determine the dislocation rate after this procedure.

From January 1993 to December 2000, 54 patients underwent isolated head and liner exchange performed by two surgeons. These patients have been followed bi-annually with clinical and radiographic evaulation. There were 36 males and 18 females. Diagnoses at the time of revision surgery were recurrent dislocations in 27 and osteolysis in 27.

The overall dislocation rate was 11% (6/54). In the 49 non-constrained revisions, a 28 mm diameter femoral head was used in 27 and a 32 mm head in 22. At the time of revision, 60% of the femoral heads were lengthened, 40% were increased in diameter, and 25% were increased in both dimensions. Hooded or later-alised liners were used in 55% of the revisions. Operative stability was documented in all operative notes, and in 85% Ranawat’s sign was used to determine liner placement based on relative component version. The dislocation rate in the non-constrained revisions was 8% (4/49). Two out of five constrained revisions, performed for recurrent dislocations, subsequently dislocated. In this study isolated head and liner revision had a comparable dislocation rate to full revision total hip arthroplasty.

Fluid pressure generated in the hip during activity has been implicated in component loosening. Animal studies show both the adverse effect of direct pressure on osteocytes and the resorption of bone subjected to cyclic loads. Pressure fluctuation measured in contained pelvic osteolytic lesions during manipulation of the hip at revision surgery suggests cyclic pressure may have a direct effect on bone resorption leading to pelvic osteolysis.

To determine the cause of pressure fluctuation in pelvic structures supporting a hip implant, we conducted an experimental and numerical analysis of relative motion at modular interfaces of acetabular cups as load was applied and removed.

We showed that for polyethylene bearing inserts supported primarily at the rim, the application of cyclic load caused cyclic motion between the insert and the inside surface of the acetabular shell. In a fluid environment, this motion can generate cyclic pressure pulses that may be applied to bone directly through the holes in the shell provided for screw fixation.

We conclude that motion at modular interfaces of acetabular components may contribute to pelvic osteolysis. Our hypothesis is that the motion of a bearing liner under cyclic load can produce fluctuating pressure pulses that are applied to bone directly through screw holes. In addition, the pulses may aid the transport of polyethylene wear debris particles into fixation interfaces. It is possible that lytic lesions previously associated with backside wear of the liner may be related to pumping of joint fluid by the liner.

We report a three year Medical Devices Agency and Local Ethical Committee approved prospective study for a new tri-tapered polished cannulated cemented femoral component. Our stem was implanted in 53 primary total hip replacements. Eleven male patients (11 hips) and 39 female patients (39 hips). The mean age at surgery was 73 (range 65 to 84). The mean weight was 71.76 kg (range 49.3 kg to 94.6 kg) with a mean BMI of 28 (range 20.20 to 40.26). All patients had a pre operative diagnosis of osteoarthritis. All the hips were implanted via the anterolateral approach. Twenty-six (51%) hips were implanted by a single consultant and 24 (49%) were implanted by six different registrars. Pre-operative and sequential post-operative clinical and radiological evaluations were undertaken.

The mean pre-operative Oxford hip score was 47 points.which declined 19 points at three years. Radiological analysis, using the Johnston criteria, did not reveal any untoward features. Prosthetic stem migration was measured using a technique developed in our unit and validated as accurate to 0.61 mm; as previously reported. Stem migration measured averaged 1.38 mm (n=52; sd ±1.38) 6 months post implantation. This progressed to 1.71 mm (n=50; SD=1.18) at one year; 1.61mm (n=48; sd ±1.17) at 2 years. and 1.55 mm (n=28; SD 1.13). At 3 years average stem migration for hips implanted by the registrar group and the consultant group was not sig-nificantly different (p=0.2048) and the migration curve, against time was similar for both groups.

Our study has demonstrated initial component migration, comparable to that of other polished tapered cemented stem designs. The improvement in Oxford hip score parallels other reported series and no adverse radiological signs have been observed. Long-term surveillance of our cohort will provide further data to compare the new design with substantial equivalents. More sophisticated studies, such as RSA analysis would provide further data on early femoral component migration.

Prevention of joint dislocation after total hip arthroplasty (THA) is important to keep suitable relationships between surgeons and patients. Capsule has an essential role for stability of joint, especially in hip. Reserving a part of capsule in THA can increase stability. We examined the effect of partial capsulotomy in hip joint for prevention of dislocations after THA.

In 178 primary THA for osteoarthritis, partial capsulotomy were performed in 92 cases and generous capsulectomy in 86 cases from 1993 to 2001. Age, gender, pre-operative complications of both groups were matched. All THA were performed from a posterior approach, and in case of partial capsulotomy, anterior one third of hip joint capsule was reserved before placing acetabular component. Posterior capsulorrhaphy was not performed.

No hip dislocations have been seen in partial capsulotomy cases, and four posterior dislocations following THA were observed in general capsulectomy cases during one to nine year follow up.

Soft tissue imbalance of THA is most at risk for dislocation. The present study showed a satisfying result of partial capsulotomy for prevention of THA dislocation. Residual hip joint capsule can increase joint stability and can resist to dislocation after THA in osteoarthritis.

The aim of this study is to compare the clinical results of the Pin-Sleeve System (AI Wiring System; AIWS) with the Dall-Miles Cable Grip System (DMCGS) for reattachment after dissection of the greater trochanter in hip arthroplasty.

The DMCGS was used in 33 cases 35 hips from 1994 to 1998 and AIWS in 40 cases 42 hips from 1998 to 2001. The age at operation was 61.3 years (24 to 85 years) in the DMCGS group and 67 years (24 to 86 years) in the AIWS group. The postoperative follow-up period was 24 months (4 months to 54 months) in the DMCGS group and 30 months (11 months to 42 months) in the AIWS group.

Bone union failure of the great trochanter occurred in the DMCGS group eight hips (22.9%) and AIWS group five hips (11.9%). The DMCGS group four hips (11.4%) had broken cables, while not even one case of the AIWS group had them (p< 0.05). Fragments from the cable were found in the DMCGS group seven hips (20%) and AIWS group two hips (4.8%). Bone resorption around the cable, grip or sleeve occurred in the DMCGS group 19 hips (54.3%) and AIWS group five hips (11.9%) (p< 0.05). Clinically, the DMCGS group 13 hips (37.1%) and AIWS group seven hips (16.7%) had dysphoria at the greater trochanter; the DMCGS group 17 hips (48.6%) and AIWS group eight hips (19%) had pain at the greater trochanter in the recumbent position with the affected side down (p< 0.05); the DMCGS group 13 hips (37.1%) and AIWS group six hips (14.3%) had pain on exertion.

The AIWS is considered to be a useful implant for reattachment of the greater trochanter compared with the DMCGS.

The most common reason for possible complications after total hip replacement (THR) surgery is improper positioning of the implant components within the hip joint. Systems for computer assisted planning and navigation during THR have been developed. However, these established modules focus on the acetabular implant component only; disrespecting the fact that proper implant functioning relies upon correct placement of both components relative to each other. Therefore, we developed an extension to the existing CT-based SurgiGATE-Prosthetics system (Medivision, Oberdorf, Switzerland) for planning and placing of the acetabular component to give the surgeon a tool, which can help him/her to also plan and insert the femoral implant.

Preoperatively, the appropriate size and position as well as the orientation of both implants components were planned. Following navigated cup placement a dynamic reference base (DRB) was fixed to the thighbone and the registration procedure was executed. For the preparation of the femoral cavity a modular PPF rasp system (Biomet-Merck, Darmstadt, Germany) was developed. All surgical action was visualised graphically within the patient’s image data. In addition, the surgeon was provided with real-time information about the depth of tool insertion, antetorsion angle, varus/valgus deviation, and the postoperative change in leg length and lateralisation of the hip joint.

After extensive validation and accuracy analyses performed on plastic models the presented system was used during one operation. An extended clinical study is currently being started.

We expect that the developed application will help the surgeon to better plan the appropriate size and position of the both parts of a hip endoprosthesis and will supply intraoperative feedback of the position of the surgical instruments relative to the patients’ anatomy and to the preoperative plan. Safer and more accurate placement of the implants components during free-hand THR surgery may be expected from this technology.

The actual data about prevalence of knee osteoarthritis, the concurrent increasing of mean age and therefore the high social costs for the care of this pathology, make particularly important to do the correct choice in knee artroprosthesis. In this work we mean compare three different type of knee prostheses implanted in our institute. We have evaluated 120 patients (98 females, 22 males) treated with TKR in I° Orthopaedic Division of Istituto Ortopedico “Gaetano Pini” – Milano. All patients were affected by primary knee osteoarthritis of high degree and 3 groups were made due to the type of prosthesis implanted.

Our evaluation protocol includes: 1. Local objective examination and evaluation of Range of Motion (R.O.M.); 2. Subjective functional questionnaire (Lequesne Index modified for knee osteoarthritis); 3. Stabilometric evaluation for Proprioceptive knee structures (KAT-2000 Breg Inc. USA); 4. Standard X-Ray, both in AP and lateral planes, with patient in standing position.

The X-Ray controls showed no early mobilisations or malfitting of all implants. In consideration of the short follow-up period we have to do a continuous monitoring for at least 5 years to express a definitive evaluation of implant stability; significatively better results regarding the post-op R.O.M. and subjective results with Lequesne Index have been obtained with the use of mobile plate prosthesis.

The first results have pointed out better results in the use of a fully mobile plate prosthesis, compared with the other results using rotating and fixed plate prostheses.

In our opinion this is obtained through the research of a better reproduction of human anatomy and trying to respect the common kinematics of knee, which has to be the future objective in design and technical development of knee arthroplasty.

Rotational mal-alignment of the patella-femoral interface will result in increased wear. Highly cross-linked polyethylene will decrease wear even if mal-aligned.

A biomechanical model based on high load and flexion was used to measure wear of rotationally aligned and mal-aligned all-polyethylene patellae. The components were articulated against “aligned” and “mal-aligned” (60 internally rotated) femoral components. The patella were subjected to a constant 2224 N force and the femoral components rotated from 600 to 1200 at 1.33 Hz. Patellae of identical geometry made of conventional UHMWPE and highly crosslinked UHMWPE were tested to 1 000 000 cycles. Wear was determined by gravimetric measurement relative to cemented soak controls.

Conventional UHMWPE: All samples demonstrated damage (burnishing and scratching) of the articulating surfaces. There was a significant increase in wear (p< .05) in the mal-aligned patella.

Highly cross-linked patellae: All components fractured in the mal-aligned construct (gamma irradiated remelted n=6, gamma irradiated and annealed n=2). Failure first occurred at the cement interface then at the posts.

Correct femoral rotation is important during TKA. The intertrochlear line, tibial cut, epicondylar axis and posterior condyles are helpful landmarks, but there is still eyeball control of rotation. It is clear from this study that rotational mal-alignment will result in increased polyethylene wear.

Highly cross-linked polyethylene has decreased wear in THA. Unfortunately, the decrease in ductility and toughness may make the use of these materials unsuitable for TKA. Based on this study model, patellar components would need to be redesigned if highly cross-linked polyethylene were to be applied.

The wear rate of conventional UHMWPE patellae is increased by rotational mal-alignment. Highly cross-linked components were a poor solution to problem. Use of highly cross-linked polyethylene resulted in component fracture.

Recently, highly cross-linked polyethylene has been highlighted in THAs which is thought to reduce wear. However, little is known about an accurate nature of cross-linked polyethylene particles and long term wear in vivo. One of the authors implanted all polyethylene cups irradiated by 100 Mrad in 1970s. Recently, we performed two revisions with this cup. In the present study, we extracted polyethylene particles and made direct wear measurements on retrieved cups.

Case one was revised for a stem fracture and acetabular loosening at 25 years postoperatively and case two for acetabular loosening at 27 years postoperatively. There was no osteolysis on X rays. We extracted polyethylene particles using a tiussue digestion and image analysis developed by Cambell and measured wear of retrieved cups using casting and 3D scanner developed by us.

Equivalent circle diameter (ECD) was 0.73 um, roundness was 0.69, aspect ratio (AR) was 1.4 and number of particles was 6.0 hundreds million/g wet tissue in case one. ECD was 0.57 um, roundness was 0.62, AR was 1.54 and number of particles was 5.8 hundreds million/g in case two. SEM showed that granule or globular shapes were abundant and fibril shapes were rare. Direct wear measurement showed concentric wear patterns were observed with very low linear wear (less than 0.03 mm).

Cross-linked polyethylene particles were less, a little smaller and much rounder in compared with our previous result of conventional polyethylene in peri-implant tissue. No unidirectional and significant amount of wear was observed in retrieved cups even after over 25 years.

Orthopedic surgeons are taught to remove the under surface of the patella in accordance with the thickness of polyethylene used to replace an equivalent amount of bone. Inability, however, to obtain a symmetrical removal of bone can lead to subluxation, increased tension producing pain, and affect range of motion. A convenient and fast way to recognise this asymmetry and remove an additional sliver of bone from the patella would be an advantage in creating a patella of even thickness.

Eight orthopedic surgeons were asked to evaluate 24 pre-cut patellar specimens with varying asymmetric thicknesses in a bag without visualisation. By feeling the patella between the thumb and forefinger, they were instructed to identify the thickest portion of the patella as well as to determine the difference in thickness between the thinnest and thickest sides. Two trials were conducted with each orthopedic surgeon consecutively.

Orthopedic surgeons were able to determine through proprioception the thickest one-half of the patella 91% of the time. This did correlate with experience in total knee arthroplasty. They were able to differentiate a 1 mm difference in patellar asymmetry 36% of the time, a 2 mm difference 61% of the time, and a 3 mm difference 81% of the time.

Orthopedic surgeons can identify an asymmetrically cut patella by assessing thickness of the patella between their thumb and forefinger the majority of the time. By doing this technique, inadvertent asymmetrically thick patellas at the time of total joint arthroplasty can be min-imised. This technique should be incorporated into the standard regimen of performing total knee arthroplasties.

Common problems following total knee arthroplasty include tibial component malpositioning, ligament imbalance, and clinical and subclinical fat embolism associated with intramedullary alignment guides. Tibial component malaligment can lead to component loosening. Ligament imbalance can lead to dysfunction and the need for revision. Fat embolism had been shown to occur in 46% of unilateral and 65% of bilateral total knee arthroplasty patients with neurological sequelae in 2 and 4% of patients respectively (Kim YH, J. Arth. 1999). All three of these common problems can be addressed with the use of surgical navigation.

Instruments designed for the Genesis II total knee arthroplasty (Smith-Nephew, Memphis, TN) are tracked optically using the ION virtual fluoroscopy surgical navigation system (Medtronics SNT, Louisville, CO). A software system specifically designed for TKR navigation is employed. Following exposure, reference frames are attached to the femur and tibia and fluoroscopic images of the knee are obtained. Hip and Ankle centres can be determined either kinematically or with images. Proper alignment and component rotation is determined using navigation without intramedullary alignment guides. Proper implant sizing is determined before the cuts are made by superimposing images of the proposed implants into the fluoroscopic images of the knee. Motion and ligament integrity can be quantified kinematically. The system was used to perform total knee arthroplasty on 14 cadavers. Post-operative alignment was measured radiographically.

As compared to the mechanical axis measured radiographically, the coronal femoral alignment measured 0.03 degrees of valgus (95% confidence:−1.81 to 1.88 degrees). Coronal tibial aligment measured 0.88 degrees of valgus (95% confidence: −2.17 to 0.41 degrees). Sagittal tibial aligment measured 1.81 degrees of posterior slope (95% confidence: −0.14 to 3.76 degrees)

The use of surgical navigation for TKA results in appropriately aligned implants. Surgical navigation has the potential to improve many of the most common problems encountered during and following total knee arthroplasty including component malaligment and malsizing, malrotation, ligament imbalance, and fat embolism.

Correct placement of the total elbow endoprosthesis is a critical factor for the long-term success of an artificial joint. Correct restoration of the centre of rotation is essential for optimal outcome. To evaluate whether surgical navigation has the potential to improve accuracy during Total Elbow Arthroplasty (TEA), an existing CAS system was applied on one plastic model and three patients.

The spine module of the SurgiGATE™ navigation system (Medivision, Oberdorf, Switzerland) was used. To apply it during TEA, a standard 3.5-mm drill guide was instrumented with infrared LEDs and calibrated. A dynamic reference base (DRB) was developed. Its base consisted of an X-shaped, scissors-like construct that could be clamped rigidly onto the distal humerus after exposure. On a plastic model, the DRB design was evaluated, and three landmarks suitable for intraoperative matching were identified. Subsequently, the Spine system was applied during three TEA surgeries. For the first surgery no pre-operative CT scan was acquired, but the design of the DRB, its camera visibility, and the accessibility of the landmarks were verified. For the other cases, the elbows were CT-scanned preoperatively. Planning consisted of 3-D segmentation as well as the definition of matching landmarks and a trajectory representing the position of a Steinmann pin, with which the humeral implant position is defined. Intraoperatively, the DRB was fixated, and matching was performed. Using the navigation system, the drill guide could then be aligned with the planned trajectory.

For the second patient, no accurate matching was achieved, hence surgery was completed conventionally. The last patient could be registered precisely, and the Steinmann pin was placed as planned.

Preliminary results show that CT-based navigation can be applied during TEA. Given a positive output of an ongoing clinical study, the development of a special TEA navigation system is planned.

Acetabular component malposition is the cause of half of all cases of recurrent hip dislocation. Intraoperative xrays after component insertion are helpful, yet it is certainly more useful to know the exact component position before final component insertion. The current study reviews results of acetabular component positioning using surgical navigation.

A prospective study of acetabular component positioning using surgical navigation was conducted in 22 hips of 21 patients. The technique involves insertion of a dynamic reference frame onto the pelvis during the surgical exposure and the acquisition of AP fluoroscopic views of each hip. Using the Fluoronav software and the ION surgical navigation system (Medtronics, Louisville, Colorado) a virtual horizontal line was then drawn between the teardrops. Acetabular component abduction was then aimed for 41 degrees. Component abduction was measured intra-operatively during component insertion by measuring the angle between the acetabular insertion handle and the virtual horizontal line between the teardrops. Post-operative xrays were analyzed for acetabular component abduction angle.

Using surgical navigation and aiming for 41 degrees of abduction resulted in post-operative cup positions averaging 40.8 degrees (range 37 to 44 degrees). These results show dramatically improved accuracy as compared to 85 acetabular component inserted without navigation showing a mean abduction of 42.8 degrees but with a range of 25 to 59 degrees. Frame placement and image acquisition required about 10 minutes. All intra-operative imaging after component insertion in complex cases was unnecessary. Having the dynamic reference frame in place also allowed assessment of pelvic position during surgery. Pelvic orientation varied greatly between patients on the operating table from about 12 degrees abducted to 12 degrees adducted. Further, pelvic orientation varied during surgery.

Surgical navigation allows extremely accurate positioning of the acetabular component at the time of total hip replacement surgery with an accuracy far greater than any study of acetabular component positioning reported in the literature. The pelvis is typically not orthogonal to the operating table during total hip arthroplasty and its position varies widely between patients and in the same patient during the procedure. Since acetabular component malposition represents the cause of half of all cases of recurrent dislocation, surgical navigation has been shown to directly address and potentially eliminate the problem of acetabular component malposition.

It is well established in the literature that the tribological properties of sliding metallic and ultra-high molecular weight polyethylene (UHMWPE) counterfaces are a major contributor to accelerate wear rates that contribute to osteolysis. The majority of the research over the years has been on improving the UHMWPE properties through manufacture and secondary processing of the polymer. Little attention has been directed towards the optimisation of the Chromium Cobalt Molybdenum (CrCoMo) surface finish.

The focus of this research has been on the highly polished CrCoMo metallic surface. A new surface finishing technique was applied to CrCoMo femoral knee prosthetic implants. The surface finish of our finished implants was compared to that finished by traditional mechanical polishing techniques. A representative number of polished CrCoMo knee femoral components were compared under the following topics; tribological, topographical and the extent of processing containments present.

It was found that traditional mechanically polished parts contained a significant amount of embedded polishing compounds (Al2O3), coarse interdendritic (M7C3) and fine (M23C6) carbide elements. Both the polishing containments and carbide elements stand proud of the articulating surface and thus act as micro cutting tools to accelerate UHMWPE wear. The new polishing technique completely eliminated hard carbide particles and embedded polishing compound media. Consequently, the samples prepared using the new polishing technique produced lower UHMWPE wear debris and improved wear patterns to that of the traditionally polished samples. Additionally, all sub-micron scratching was removed from the surface of the samples.

This polishing technique for CrCoMo prosthesis represents a milestone in CrCoMo surface finishing and will significantly reduce the UHMWPE wear debris generated and consequently increasing prosthesis longetivity.

Today’s major challenge for total hip arthroplasty is to minimise wear and osteolysis in our younger and more active patients. Alumina ceramic bearings have known superior wear resistance and lubrication and do not carry a risk of ion release. Utilising new improved alumina ceramic materials and implant design 514 hips were implanted in a multicentre US IDE prospective and randomised study. The study compared alumina-on-alumina ceramic bearings to a cobalt chrome-on-polyethylene bearing.

All patients received the same press-fit hydroxylapatite coated femoral stem while two-thirds (349 hips) received alumina ceramic bearings and one-third (165 hips) received the cobalt chrome on polyethylene bearing. All patients suffered from non-inflammatory arthritis and were young and active with an average age of 53 years.

At a follow-up of 24–60 months (mean 39.8 months) there was no significant difference in clinical performance between the patient cohorts.

Utilising a new implant design and improved alumina ceramic materials, 514 hips were implanted in a US IDE prospective, randomised study. All patients received the same press-fit hydroxylapatite (HA) coated femoral stem. Two-thirds (349 hips) received alumina ceramic bearings, and one-third (165 hips) received CoCr heads on polyethylene liners. The alumina group was further divided. Approximately one-half (172 hips – System I) received a porous-coated titanium shell and an alumina insert, and one-half (177 hips – System II ) received a HA-coated, arc-deposited titanium shell and an alumina insert. System III (the control) consisted of a porous-coated titanium shell and a polyethylene insert. External geometry of all shells was identical.

An independent orthopaedic surgeon who did not participate in the study reviewed all radiographs. At latest follow-up, (minimum 2 years; range 2-4 years), differences were noted in the developmental pattern of the radiolucent line around the acetabular component. Radiolucent lines were most often noted with System I and System III (porous acetabular shells) in De Lee and Charnley Zone 3 and were absent in System II (arc-deposited titanium with HA) (p=0.001). Other standard radiographic parameters evaluated were found to be comparable, with one exception: In 10 cases in the control group, the development of a small erosive lesion (scalloping) in femoral Gruen Zone 8 was observed on the lateral film. This compares to two cases in System I, and no cases in System II (p=0.001).

Dislocation rates were comparable for all three Systems. Seven acetabular components were revised: one in System I, three in System II and System III. The two revisions for aseptic loosening were both in the control group.

This study measured polyethylene wear and correlated it with design features such as tibiofemoral conformity and contact areas.

Two femoral component designs were tested in a knee wear simulator. The femoral condyles of design A were flat-on-flat in the coronal plane, while those of design B were curved-on-curved. These femoral components were tested with two inserts. Insert PLI had a posterior lip, while insert C had a more curved sagital geometry, to improve stability in the anteroposterior direction. All components were tested for up to five million cycles in bovine serum lubricant. Triaxial forces were monitored to ensure that loading conditions were similar in all combinations tested. Gravimetric wear measurements were made at 500 000 cycle intervals. Contact stresses were measured using pressure sensitive film and dynamic finite element analysis.

Contact stresses were 22% higher for inserts tested with design A compared to design B. Sliding distance, sliding velocity, and patterns of crossing motion were found to be comparable between the two femoral designs. Inserts tested with design A wore significantly more (mean 10.9 mg/million cycles) than design B (mean 5.71 mg/million cycles, p < 0.001). No appreciable differences were found between wear rates of insert PLI and insert C.

Component design can have a significant impact on polyethylene wear rate. Careful control of kinematic and loading conditions allowed for comparison between specific design features. Increase in tibio-femoral contact area led to reduction of contact stresses, which was reflected in the reduced wear rate.

The novel horseshoe shaped cup was designed by the senior authors to minimise the resection of healthy bone in total hip arthroplasty. It replaces the cartilage and underlying sub-chondral bone of the acetabulum socket with a cup that is designed to flex in harmony with the surrounding bony structure.

Fifty female patients with a displaced, subcapital, femoral neck fractures were chosen for the study. In half of the group of patients, the composite support shell was coated with HA, with the other half remaining uncoated. Clinical and radiological assessments were undertaken regularly for five years.

To date 20 patients have died and 13 have withdrawn from the study due to poor medical health unrelated to the study. Charnley modified Merle d’Aubigne score at five years was as good as the preoperative score with 80% of patients having full range of movement, no pain and walking unaided.

Radiographic results showed no evidence of loosening of HA coated cups, in contrast to non HA coated cups which migrated significantly in 80% of cases. Four patients with loose non HA coated cups underwent revision surgery.

This trial has demonstrated success at 5 years with the HA coated Cambridge Acetabular Cup. Cups from which HA coating has been removed have migrated significantly in 80% of cases. There is an advantage of the HA fixation which will be taken into account before wider clinical usage is advocated.

The site of initiation of failure of a cemented femoral component is usually the prosthesis-cement interface. Strengthening this interface with porosity reduction may improve survivorship. Cement pores which propagate crack formation can be reduced by vacuum mixing or centrifugation, but this does not effect interface porosity.

Utilising simulated stems cemented into a “Sawbones” femur in a manner replicating surgery, we determined the effect of stem warming on various parameters. Maximum temperature and time of polymerisation, mechanical strength, porosity reduction and pore distribution in the cement mantle were measured with stems at room temperature (RT), 37, 44, and 50 degrees Celcius. Mechanical testing included initial “push-out” tests, tests after agiing in 37 degrees Celcius saline for two weeks,and fatigue testing (3 HZ at 90% initial failure load). Porosity distribution was measured by the percentage area of pores on the interface surfaces and the transverse plane.

Polymerisation time decreased as the stems were heated. The time decreased from 8.1 minutes at RT to 5.9 minutes at 50 degrees Celcius. The maximum temperature in the cement mantle rose from 50.2 to 56.4 degrees Celcius comparing stems at RT to those at 37 degrees Celcius, and did not elevate further as stems were preheated to 44 and 50 degrees Celcius. Similarly, static and fatigue interface strength improved by preheating stems, but no significant gain compared to RT stems was realised by heating above 37 degrees Celcius.

A dramatic reduction in porosity at the prosthesis-cement region was found with the heated stems, with no additional benefit to heating beyond 37 degrees Celcius. An increase in porosity at the cement-bone interface was noted as stems were heated. This may be due to the direction of polymerisation shrinkage in the cement mantle as influenced by stem temperature.

Although hydroxyapatite (HA) coating is known to enhance fixation in THR, its role in the fixation of Total Knee Replacements is less well appreciated. This study was performed to assess the medium-term results of an HA-coated TKR.

Between August 1992 and 1998 all patients requiring a primary TKR were treated with a hydroxyapatite-coated, PCL-retaining prosthesis implanted by the senior author. The HA coating used was 70 microns thick with 75% crystallinity and 20% porosity. It is deposited on a beaded heat-sintered surface. A combined Hospital for Special Surgery and Knee Society Score was recorded pre-operatively and at three, six, 12, 24 and 60 months post-operatively. Fluoroscopically-controlled interface views were performed on the first 161 knees immediately post-operatively and repeated 24 months postoperatively.

Six hundred and ninety two patients (Male:Female 335:357) with a mean age of 68 years (31–88 years) underwent 1 000 TKR mainly for OA (93%) and inflammatory arthropathies (RA 3%, psoriasis 1%). The mean follow up was 75 months (40–115). There were 461 unilateral (R:L 256:205) and 539 bilateral replacements (462 simultaneous and 77 staged).

The pre-operative knee score was 95/200, ROM 6–115 degrees and at latest review was 182/200, ROM 1–113 degrees.

Forty four patients have died (mean age 73 years, range 54 to 88). There have been 14 deep infections (1.4%), 22 proven pulmonary emboli (2.2%) and five periprosthetic fractures (0.5%). Six revisions have been performed. Visible gaps between bone and implant were present in 91% of femora and 58% of tibiae initially and in 6% of femora and 8% of tibiae at two years on interface views. There have been no cases of clinical loosening.

Currently, this study comprises the largest known series of HA-coated total knee replacements. These results demonstrate that HA appears to enhance fixation of uncemented knee prostheses which maintain good clinical outcomes.

Polyethylene contact stresses have been shown to correlate with wear in total hip arthroplasty (THA). Several liner designs have been introduced in an attempt to increase stability or reduce impingement and increase range of motion. This study analyzed the effect of liner design on range of motion (ROM) and PE contact stresses in a finite element model (FEM).

FEMs of four liner designs were generated: Generic was modelled as a simple hemisphere, Chamfer had a wide chamfer on the inner edge of the liner to increase ROM, Highwall had an extended lip to increase stability, and Anteverted created a 20° anteversion with lat-eralisation of the centre of rotation. With the liners in varying positions of abduction and anteversion, physiologic loads were applied through the femoral head. Hip ROM was measured by rotating the head and neck in different directions until prosthetic impingement.

Significant differences in ROM were seen relative to the Generic liner. Chamfer increased ROM by mean 16%. Highwall reduced ROM by mean 12%. Anteverted increased flexion by 17% but decreased extension, abduction, and external rotation. Contact stresses were also significantly affected by liner design and acetabular orientation. Overall for the same acetabular position, contact stresses were higher for Chamfer and lower for Highwall and Anteverted.

These results underline the complex interaction between cup design, hip stability, range of motion and contact stresses. Design features that increase stability tend to reduce contact stresses and ROM, while those features that increase ROM, tend to increase contact stresses. This data can help the surgeon match liner design to specific patient requirements.

The objective of this present study was to determine the in vivo kinematic patterns for subjects implanted with a patellofemoral arthroplasty (PFA).

Twenty subjects, all having a PFA, were studied (< 2 years post-op) under fluoroscopic surveillance to determine patellofemoral contact positions, sagittal plane, and medial/lateral translation using a skyline view.

The patellofemoral contact patterns for each subject having a PFA was highly variable, 11.9 mm of translation. The average amount of patella rotation during the full flexion cycle was 26.3 degrees, while one subject experienced 48.6 degrees. The average amount of medial/lateral translation was 3.8 mm (5 > 5 mm). Five subjects experienced grater than 5 mm of motion.

This was the first study to ever determine the in vivo kinematics for subjects having a PFA and the in vivo medial/lateral translation patterns of the patellofemoral joint. Subjects in this study experienced high variability and some abnormal rotational patterns. Most of the subjects who underwent PFA in this study had a previous history of subluxed or dislocated patella which affects the normal patella tracking, especially regarding tilting and translation. This tracking may also be directly affected by patellofemoral conformity, a consequence of femoral implant design. Finally, after PFA the patello-tibial tilt angle is influenced by the anteroposterior positioning of the femoral component.

The results of this very first in vivo kinematic study may play an important role, not only for design consideration of patellofemoral replacement but also for surgical technique in order to obtain optimal implant positioning.

The objective of the present study was to analyse kinematics of subjects having a UKA during stance phase of gait, where the ACL was intact at the time of the operative procedure.

Femorotibial contact positions for nineteen subjects (15 medial UKA (MUA); 14 lateral UKA (LUA); HSS > 90, post-op > 3 yrs) were analysed using video fluoroscopy.

During stance-phase of gait, on average, subjects having a medial UKA experienced 0.8 mm of anterior motion (7.7 to – 2.3 mm), while subjects having a lateral UKA experienced −0.4 mm (0.9 to – 2.1 mm) of posterior femoral rollback (PFR). Eight of 15 subjects having a medial UKA and two out of four lateral UKA experienced PFR. Eight of 15 subjects having a medial UKA experienced normal axial rotation (average = 0.9 degrees) and one out of four subjects having a lateral UKA experienced normal axial rotation (average = −6.0 degrees).

High variability in the kinematic data for subjects experiencing an anterior slide and opposite axial rotation suggests that these subjects had an ACL that was not functioning properly and was unable to provide an anterior constraint force with the necessary magnitude to thrust the femur in the anterior direction at full extension. Progressive laxity of the ACL may occur over time, and at least in part, lead to premature polyethylene wear occasionally seen in UKA. Our results support the findings of other studies that the ACL plays a significant role in maintaining satisfactory knee kinematics, which may also, in part, contribute to UKA longevity.

Improved cement technique by interposing less than two layers of hydroxyapatite (HA) granules between bone and bone cement at the cementing (Interface Bio-active Bone Cement : IBBC) have been performed in total knee arthroplasty (TKA) since 1987.

We performed IBBC technique in 153 knees (130 patients) in TKA from 1987 to 1993. One hundred and forty knees (120 patients) could be followed up clinically and radiologically. Follow up rate was 91.5%. A mean follow-up period was 9.5 years (6 to 13 years) after surgery. As a control, clinical results of TKA with conventional cementing (Non-IBBC) which were operated in 44 knees (44 patients) in 1986 were used.

In IBBC cases, radiolucent lines on the tibial components were seen 7.1%, 2.9%, 1.4%, 3.6%, 0%, 0% and 0% at Zone ‡T to ‡Z of the anteroposterior view, while in Non-IBBC cases, 40.9%, 13.6%, 9.1%, 27.3%, 11.4%, 4.5% and 13.6% at Zone ‡T to ‡Z, respectively. In IBBC cases peri-prosthetic osteolysis of the tibial components were seen in three knees (2.1%), while 29.5% in Non-IBBC cases. Aseptic loosening of the tibial component was only one case (0.7%) in IBBC cases, while 9.1% in Non-IBBC cases.

In IBBC, bone cement bound to HA mechanically immediately after surgery and HA granules bound to the bone physicochemically after bone ingrowth into the spaces around the HA granules. In Non-IBBC, spaces will appear between bone and bone cement due to osteoporosis and/or atrophy after long years. However, in IBBC, bone and bone cement will contact by interposing HA forever due to osteoconductive effect of HA.

In conclusion, the IBBC has significantly reduced the incidence of radiolucent lines and periprosthetic osteolysis in TKAs. IBBC is a method combining the advantage of cementless HA coating and bone cement.

We have used Interface Bioactive Bone Cement (IBBC) in all cases of total joint arthroplasties since 1987. The method is improved cement technique by interposing less than two layers of hydroxyapatite (HA) granules between bone and the polymethylmethacrylate (PMMA) bone cement. We report one patient who underwent revision surgery after total knee arthroplasty (TKA) using IBBC.

The patient is a woman aged 70 years at the time of revision surgery. Right TKA was performed with the diagnosis of rheumatoid arthritis. An alumina ceramic total knee prosthesis was inserted using IBBC. Pain and walking ability were once improved after the primary TKA. However, the gait disturbance recurred after the patient fell on the ground. Radiographic findings showed severe genu varum, but neither radiolucent lines around the components nor migration of the components were seen. This was revised with semiconstrained prosthesis for the purpose of improving lateral instability at 31 months after the primary TKA.

Avulsion of fibular attachment of collateral ligament was seen at the time of the revision surgery. As PMMA cement was strongly adhered to the bone, it was removed together with cancellous bone. Histologically, HA granules bound to the bone directly after bone ingrowth into the spaces around the HA granules. This is the reason we have described IBBC as a method having the both advantages of cementless HA coating and PMMA bone cement.

After the revision surgery, the walking ability was improved.

In conclusion, this case showed excellent characteristics of IBBC.

The objective of this present study is to conduct a comparative analysis of the kinematic data derived for all subjects having a TKA who were analysed over the past eight years at our laboratory.

Femorotibial contact positions for 705 subjects having either a fixed bearing PCR or PS TKA or mobile bearing TKA were analysed in three-dimensions using video fluoroscopy.

During a deep knee bend, all PS TKA types subjects experienced a medial pivot motion, averaging −3.8 of lateral condyle posterior femoral rollback (PFR), respectively. Subjects having a fixed bearing PCR TKA experienced only −0.7 mm of lateral condyle PFR and an anterior slide of 1.6 mm for the medial condyle. Twenty-nine percent of the PCR TKA analysed had a lateral pivot and 71% experienced a medial pivot. Subjects having a mobile bearing TKA experienced −2.8 mm of lateral condyle PFR and 0.4 mm of medial condyle anterior slide. Fifty-one percent of the moble bearing implants experienced a medial pivot and 43% experienced a lateral pivot. During gait, PS and PCR fixed bearing TKA types experienced similar kinematic patterns. Subjects having a mobile bearing TKA experienced minimal motion, probably due to the mobile bearing TKA having greater sagittal conformity and had the lowest standard deviation.

There was great variability in the data comparing various TKA designs. Subjects in this multicentre analysis predominantly experienced a medial pivot motion, although certain TKA designs did demonstrate a lateral pivot motion.

The use of exhaust suit systems is commonplace in arthroplasty surgery where isolation of the surgical team is desirable in an attempt to reduce the risk of infection transmission. Elevated carbon dioxide levels have been reported in the non-clinical setting with such systems the consequences of which can include fatigue, diapho-resis, nausea, headache and irritability.

The aim of our study was to determine the levels of carbon dioxide present within an exhaust suit system during hip arthroplasty and to compare these with the recommended occupational exposure limit levels published by the Health and Safety Executive (HSE).

Data was collected during ten primary hip replacements performed by the same surgeon whilst wearing the Stryker Steri-Shield Helmet Exhaust System. This is a self-contained unit with an integrated blower used in conjunction with a full-length gown. In addition the helmet was fitted with an air-sampling probe connected to a portable infrared CO2 monitor and also a temperature probe. Thus continuous monitoring of both CO2 and temperature level during surgery was possible.

The mean initial CO2 concentration in the helmet at the beginning of surgery was 3 000 parts per million (ppm) and the mean maximum CO2 level recorded was 13 000 ppm. The mean time the surgeon was within an exhaust suit to perform a primary hip replacement was 1 hr 54 mins and for 86% of this time period the CO2 level within the helmet exceeded the recommended level of 5 000 ppm as stipulated by the HSE.

In conclusion we have demonstrated significantly elevated CO2 levels within the Stryker Steri-shield Exhaust Suit System during hip surgery. Surgeons who use this system should be aware of this together with the physical symptoms that may result.

Initial fixation affects ingrowth of uncemented tibial components. Previous studies assessed initial fixation, however most used limited one-dimensional motion measurements. Therefore, a three-dimensional micro-motion and migration analysis was performed to compare initial fixation of four different tibial tray configurations: 1) Keeled component 2) Non-keeled component (post but no keel) 3) Keeled component with screws 4) Non-keeled component with screws.

Osteonics series 7 000 tibial trays (identical to Scorpio design) with and without standard keels were obtained. The 30 mm posts were left intact. The components were implanted without cement into twenty-four fresh-frozen cadaveric tibiae. Specimens were loaded through matched femoral components via two separate loading conditions: 1) sinusoidal medial load from 200 to 2 200 N at 0.5 Hz and 2) sinusoidal torsion load from −5 Nm to +5 Nm at 0.5 Hz with constant 1 200 N axial load. Motion data were collected from reference cubes and transducers rigidly attached to the trays, during 3 000 cycles of loading. Rigid-body mechanics were used to calculate the motion of a wire-frame computer model. Comparisons were made of micro-motion and migration magnitudes.

A keel did not significantly decrease micromotion or migration under medial or torsion loading compared to a post alone (p=1.04). The addition of four cancellous screws decreased motion (p< .05) regardless of the presence of a keel under medial loading. No significant differences were noted under torsional load for any tray configuration.

A keel did not enhance initial fixation compared to screws or a post alone. Screws enhanced fixation under axial offset loading in all constructs. Screw fixation did not affect motion under torsion loads perhaps due to the limited magnitude of torque transmitted across the unconstrained femoral-tibial articulation. Based on these data, initial fixation of uncemented tibial implants should include screw fixation to counter the effects of offset axial loads.

Large diameter metal on metal hip bearings have been shown to display exceptionally low wear in vivo. However, as these components are often cast, they may be heat treated to improve homogeneity, although it has been suggested that this may adversely affect wear. Therefore a hip simulator study was commissioned to investigate this further.

Multi-station hip simulator testing was carried out on 40 mm diameter high carbon cast cobalt chrome alloy components, all having similar radial clearances (~100mm), surface finishes (0.01mm Ra) and sphericity deviations (< 10mm). Three bearing couples were hot isostatic pressed (HIPed) and solution heat treated, generating a fine carbide structure, and three bearing couples were left as cast, creating a coarse carbide structure. All sockets were mounted in an MTS hip simulator, inclined at 35° to the horizontal, and subjected to standard walking conditions (2450 N max) using 25% bovine serum as a test lubricant. Wear was calculated gravimetrically using temperature controls.

Running-in wear was observed for both groups generating a similar combined head and cup mean wear rate of 2.3 mm3/106 cycles. The mean steady-state wear rate (SE) for the as cast and HIPed components was 0.38 (0.13) and 0.57 (0.11) mm3/106 cycles respectively showing no statistical difference (p > 0.2). Wear was generally higher for the cups than the heads.

These wear rates are two orders of magnitude lower than published wear rates of metal-UHMWP E under similar conditions and one order of magnitude lower than lightly crosslinked UHMWPE articulating against CoCrMo under the same conditions.

In this test, the effect of HIPing and solution heat treatment on metal-metal wear would therefore appear to be insignificant. This is in contrast to the published influences of both bearing diameter and bearing tolerances, i.e. sphericity and radial clearance on the wear of metal-metal hip joints.

Since acetabular osteolytic lesions following total hip arthroplasty (THA) may be asymptomatic until extensive bone loss occurs, early detection and monitoring the progression of these lesions is important. The purpose of this study was to use high resolution helical CT to determine the progression of the osteolytic lesions over time by comparing serial studies.

Fifty patients (Fifty-eight hips) with primary, cementless THA done between 1984–1996 were evaluated as part of an ongoing prospective study. These patients had a history of a high level of activity that was believed to place them at increased risk for accelerated polyethylene wear. The mean age was 51 yrs, 55% male:45% female. The average time from date of surgery to initial scan was 8.0 years (4.7–16.6). If an acetabular lytic lesion was identified, the patients were offered Alendronate for potential suppression of bone resorption with a repeat CT scan for follow-up. The area of the maximum size osteolytic lesions on axial images were measured on the initial scan and compared at the same level on the subsequent study.

The interval between scans averaged 15 months (10 – 27). Progression was noted on 87% hips. The mean initial area was 328 mm2 (40–1084) with the follow-up area of 386 mm2 (46–1344) with a mean of progression of 15.7%.

Once established, peri-acetabular lysis appears to be a slowly progressive, relentless process. Analysis of changes on serial CT, along with an assessment of the degree and location of lysis, provides an additional tool to evaluate the need for surgical intervention.

The benefit of mobile-bearing mechanism in total knee arthroplasty (TKA) has been controversial. The aim of this paper is to analyse the rotation of polyethylene (PE) and its effect on the range of motion (ROM) in mobile-bearing, posterior stabilised TKA (LPS-Flex™, Zimmer Co. Ltd.).

Thirty-four consecutive PS-Flex™ TKAs (28 patients) were analysed. Three tantalum markers were inserted in the PE and the tibia (one for medial side and two for lateral side; total six markers). The rotation of the PE and the tibia was analysed in fluoroscopically-controlled radiograph taken at one years in full extension, 90 degrees flexion and passive maximum flexion. The markers in the tibia were identifiable in 19 knees and the analysis was based on these knees.

The tibia rotated internally relative to the femur by 7.1± 5.2 degrees (mean ± SD, range −1 to 20 degrees). The amount of tibial rotation has no correlation to ROM. The rotation of the PE relative to the femur was unpredictable showing three knees with external rotation and four knees without rotation (Average; 4.0 ± 4.5 degrees internal rotation). The rotation of the PE on the tibia was 4.2± 5.2 degrees and seven knees (37 %) showed no rotation and 12 knees (63 %) showed less than 5 degrees rotation. There was a positive correlation between the amount of PE rotation on the tibia and ROM, which approached to statistical significance (p = 0.0684).

This study has demonstrated that the rotation of the PE on the tibial tray is generally small (< 5 degrees). Because not tibial internal rotation but PE movement on the tibia correlated to ROM, the essential benefit of the mobile-bearing mechanism could be to compensate the rotational mismatch between the components rather than to reproduce normal knee kinematics.

Outcomes for a RSP to treat either a previous operated shoulder (revision procedure) was compared to a primary RSP.

Twenty primary RSP (6M, 14F) for an irreparable rotator cuff tear (IRCT) with glenohumeral arthritis /anterior superior arch deficiency and 31 revision RSP (10M, 21F) (previous rotator or cuff surgery, hemi or total shoulder arthroplasty) were evaluated at an average of 24 months postoperatively. Mean age at the time of RSP was 72.3 for primaries 67.2 for revisions. Assessment with pre- and postoperatively SF-36, SST, ASES scores, physical exam, satisfaction surveys, and radiographs was performed.

Primary RSP improvements /Revision RSP improvements were: 9.4 sf-36 PCS/ 6.3 sf-36 PCS, 1.8 SST/ 1.6 SST,31.8ASES / 17.5ASES (p< 0.05),49.2 elevation/ 14.2 elevation (p< 0.05) and 57.8 external rotation/ 30 external rotation. 71.3% Excellent/good/. 56% Excellent/ good (p< 0.05), 21.4% satisfactory/ 33.3% satisfactory, 7.1% unsatisfactory outcome/ 9.5% unsatisfactory outcome. Complications only occurred in the revisions including component disassociation, glenoid loosening, recurrent instability, and infection

Primary RSP provides predictable improvements in pain and function with minimal complications. Revision RSP has a higher complication rate and improvements in pain and function are less reliable. Conventional shoulder arthroplasty for patients with IRCT with gle-nohumeral arthritis/anterior superior arch deficiency has resulted in adequate pain relief but functional improvement has not been predictable. Thus, the initial operative selection for these patients must consider the effect of a failed reconstructive attempt on patient outcomes.

The determination of the cause of prosthetic failures in total hip arthroplasties can be difficult. Pre-operative imaging, including plain x-rays, tri-phse bone scan and MRI imaging have not been able to discern septic from aspectic causation. White blood cell scans, once thought specific for infection when positive, has demonstrated positivity in”wear and debris” reactions. Labs including WBC, Sed Rate, CRP can be elevated in septic, as well as, aseptic failures. Although frozen section is reliable showing acute inflammation for infection, chronic active inflammation which often is seen with chronic infections, can also be seen in aspectic failures. Cultures are often falsely positive, but in chronic infection it may be associated with less than 80% retrieval.

Five cases of acetabular loosening associated with radiolucencies around a prosthesis were studied. These cases had rapid failures and were thought to be secondary to an oil residual left after processing of an in growth prosthesis. All patients had a radiolucent zone around the bone prosthetic intersurface. The patients had increasing pain on weight bearing and a positive bone scan. Frozen section at the time of surgery demonstrated chronic inflammation and was culture negative. The acetabular prosthesis and associated parts were placed immediately in 80% Etoh and Tris buffer. Combinations of confocal laser microscopy with live-dead stains, FISH Probes for Staph., or scanning electron microscopy was performed looking for biofilm.

All five of the prosthesis or related parts showed the presence of bacterial biofilm. One of these had cement covering the porous portion.

These results demonstrate our inability to discern aseptic from septic loosening in total hip arthroplasty by the current clinical means.

Twelve pairs of fresh-frozen, cadaveric femora were harvested. Each right femur was prepared for the cemented insertion of the femoral component of a total hip implant. Left femora served as matched intact controls. Following insertion of the implants, the distal tip of the stem was identified and an oblique osteotomy was made to represent a periprosthetic fracture. Proximally, plates were secured with cables and distally by bicortical screw fixation (c+s). The twelve pairs of femora were randomly divided into three groups: 1. Zimmer Cable-Ready System, 2. AO 4.5 mm broad, LC-DCP, with Wire Mounts and Double Luque Wires, 3. Dall-Miles Cable Grip System. Specimens were mounted and deforming forces were applied to test the biomechanical stiffness of the constructs. Following testing the plate-cable combinations, the proximal cables were removed and replaced with unicortical screws (s+s). Repeat testing was then performed as per the above protocol.

The stiffness of the constructs relative to intact bone decreased (p< 0.05) with fixation utilising cables plus screws (c+s) during four-point bending (69–77%) and offset rotational loading (61–64%). When testing unicor-tical plus bicortical screw fixation (s+s) in these modes, a similar effect was seen. There was no difference between plate systems (ANOVA, p> 0.05). Comparisons of stiffness between cable plus screw combination versus unicor-tical plus bicortical screw combination revealed that the latter method of fixation (s+s) was more rigid (p< 0.05).

Our study showed that the three plate-cable systems displayed similar biomechanical stiffness. In addition, when the cables were replaced proximally with unicortical screws, more rigid fixation was obtained in all but one plane of testing.

We conclude that the method of plate stabilisation by screws or cables is more significant than the type of plate used for periprosthetic fracture stabilisation.

Impacted morsellised donor bone is succesfully used to treat bone loss in revision total hip arthroplasties. After implantation new bone is formed in the donor bone. It is generally thought, but not proven, that the processing and storage at −80°C of the donor bone kills all cells. There is however general concern about viral, bacterial, and/or oncogenetic contamination with donor bone. Based on these considerations it is essential to know whether the donor bone does contain viable bone cells.

Fragmented biopsies from eleven femoral heads from our bone bank, which is processed according to the Musculo-skeletal Council of the American Associations of Tissue Banks (AATB) and the European Association of Musculo Skeletal Transaplantation (EAMST), were tested for their capacity to give rise to proliferating cells in vitro. This was repeated with five other femoral heads from the same bone bank after irradiation. Microscopic analysis of cell growth, aspect, and number was performed on the established cell cultures. DNA marker analysis of the cultured cells and freshly obtained buccal cells from the donor was done in order to verify the origin of the cultured cells.

All fragmented biopsies showed cell growth. Cell outgrowth time as well as cell number varied between donors, and was independent of the length of storage time at −80°C. No cell outgrowth was observed from irradiated bone. DNA marker analysis showed identical alleles for cultured cells from frozen bone and DNA from freshly obtained unfrozen buccal cells from the donor.

Biopsies from femoral heads from a bone bank according to the AATB and the EAMST contain living bone cells with growth capacity. It is unclear which role these vital cells play in the process of new bone formation in the donor bed, or in the risk of contamination.

Two hundred and seventeen consecutive patients (238 hips) underwent total hip arthroplasty using the St Michael’s stem and a non-porous screw ring cup. Patients were followed prospectively clinically using the St Michael’s hip score and radiographically. At an average of 11.9 years (10-13.5 years), 55 patients (59 hips) had died, 23 patients (23 hips) were lost to follow-up. The St Michael’s hip score improved from 13.4 pre-operatively to 21.7 (out of a possible 25) at the latest follow-up. Thirty-seven (24%) of the acetabular components have been revised for aseptic loosening and an additional seven components are radiographically loose. No femoral components have been revised. Using Engh’s criteria one femoral component is definitely loose and two femoral components have stable fibrous ingrowth. Significant stress shielding was noticed in 23 hips (17%) without clinical consequences. Minor osteolysis was seen in 13 hips most commonly around the proximal femur and has not caused symptoms. The St Michael’s stem with its large pore size madreporic surface has comparable results to other porous coated stems with smaller pore size.

The St Michael’s stem provided reliable ingrowth and fixation with an acceptable degree of stress shielding. The non-porous screw ring cup had a high failure rate.

Reduction of ultra high molecular weight polyethylene (UHMWPE) surface wear in total knee replacements (TKR) may delay the onset of osteolysis and loosening of components. This study examined the wear of fixed bearing and rotating platform (RP) mobile bearing TKR with two different bearing materials.

Testing was completed on a Leeds ProSim six-station knee simulator under ‘high’ kinematics [1]. PFC Sigma fixed bearing and LCS RP mobile bearing knee designs were tested (DePuy). Non-crosslinked (non-irradiated (NI) or gas plasma (GP) sterilised) and moderately cross-linked (4.0 MRad gamma irradiation sterilisation under vacuum (GVF)) GUR1020 UHMWPE bearings were investigated for each TKR design. Components were tested in 25 % bovine serum solution for up to five million cycles (frequency = 1 Hz). Volumetric wear was determined from gravimetric measurements of the inserts.

The 1020 GVF fixed bearings exhibited a wear rate of 16.4 ± 4 mm3 per million cycles (MC). This was significantly greater (p < 0.05) than wear of the same bearing material in the rotating platform mobile bearing TKR (10.85 ± 2.39 mm3/MC). Similarly, when uncross-linked 1020 UHMWPE was introduced as the bearing material, a significant (p < 0.05) reduction in wear was observed between the fixed bearing (16 ± 7 mm3/MC) and the RP knee designs (5.85 ± 2.05 mm3/MC).

The RP design decouples the motions between the femoral-insert and tray-insert articulating surfaces. This translates complex knee motions into more unidirectional motions at two interfaces, thus reducing wear under high kinematics compared with fixed bearing TKR. This significant reduction in wear was observed with uncross-linked and moderately cross-linked bearing materials. Design of TKR is an important factor that influences UHMWPE surface wear and may affect long-term success of knee replacements in highly active patients.

Following total hip replacement surgery, fluroscopy studies have shown that a mean separation of 2 mm can occur between CoCr femoral heads and UHMWPE acetabular cups during the swing phase of gait [1]. In vivo and in vitro studies [2, 3] of alumina ceramic on ceramic hip replacements have demonstrated that swing phase microseparation followed by the impact of the femoral head on the acetabular insert rim can lead to accelerated wear. However, wear remains low. A similar trend was observed when metal on metal hip replacements were tested under microseparation conditions [4]. The purpose of the current study was to examine the wear of ceramic on polyethylene bearings under standard and microseparation conditions.

A physiological hip simulator was used, loads and motions were applied to approximate in vivo conditions. The alumina ceramic heads and polyethylene cups were 28 mm in diameter and were tested for 5 million cycles in 25% new born calf serum at 1 Hertz. Microseparation was achieved by displacing the femoral head inferiorly during swing phase, where the head contacted the inferior cup rim and was laterally displaced. On heel strike the head contacted the superior cup rim prior to relocation.

The volumetric wear of the polyethylene inserts was approximately four times less under microseparation conditions (5.6 ± 5.3 mm3 per million cycles), in comparison to standard conditions (25.6 ± 5.3 mm3 per million cycles). Deformation of the cup rim was observed, but some of this was attributed to creep. It is postulated that this reduction in wear was due to the separation of the components in swing phase improving the entrapment of lubricant, hence reducing wear via a squeeze film lubrication mechanism. In conclusion, surgical procedures that produce a small and controlled amount of joint laxity and microseparation may lead to a reduction in wear of the polyethylene acetabular cups.

Only recently has the mobility of the ankle joint been elucidated. Sliding/rolling of the articular surfaces and slackening/tightening of the ligaments have been explained in terms of a mechanism guided by the isometric rotation of fibres within the calcaneofibular and tibiocalcaneal ligaments. The purpose of this investigation was to design a novel ankle prosthesis able to reproduce this physiological mobility.

A four-bar linkage computer-based model was used to calculate the shapes of talar components compatible with concave, flat and convex tibial components and appropriate fully congruous meniscal bearings. Three-component designs were analysed, and full congruence of the articular surfaces, appropriate entrapment of the meniscal bearing and isometry of the two ligaments were required.

A convex tibial component with 5 cm arc radius gave a 2 mm entrapment together with a 9.8 mm amount of tibial bone cut, while maintaining ligament elongation within 0.03 % of the original length. The physiological patterns of joint motion and ligament tensioning were replicated. The talar component slid backwards while rolling forwards during dorsiflexion. These movements were accommodated by the forward displacement of the meniscal bearing on the tibial surface under the control of the ligaments. The complementary surfaces provide complete congruence over the entire range of flexion, such that a large contact area is achieved in all positions.

To restore the physiological mobility at the ankle joint, not only should the components be designed to be compatible with original ligament pattern of tensioning, but also these should be mounted in the appropriate position. A suitable surgical technique was devised and relevant instrumentation was manufactured. Five below-knee amputated specimens replaced with corresponding prototype components showed good agreement with the model predictions.

Current three-component designs using a flat tibial component and physiological talar shapes cannot be compatible with physiological ligament function.

Bone-cement shrinkage has never been quantified in a stem/cement/femur construct. We observed gaps around femoral stems in transverse sections of stem/cement/femur constructs; a greater proportion of stem/cement (s/c) interface gaps were found around grit blasted sections of stems than satin finished sections. If s/c gap formation were a shrinkage artifact then mantles with few s/c interface gaps must manifest shrinkage elsewhere, at the c/b interface or voids. ‘Mould-gaps’ at a c/b interface have been described previously but not quantified. We analysed the area of gaps at both interfaces. We hypothesised 1) Total gap area was the same for all transverse sections. 2) Satin sections had greater c/b gap areas than grit sections.

Transverse sections of stem/cement/femur constructs were processed to highlight gap areas. Five stems had a satin finish (Ra 0.75 um) and five were proximally grit-blasted (Ra 5.3 um). Sections were coated with matt black spray paint and then polished with emery paper. This process left all interface gaps and voids filled with black paint, which facilitated digital imaging. Gaps were visually identified and measured using Image-Pro. Gap areas for each transverse section were normalised by the area of cement in that section.

Gaps were not evenly distributed; there was obvious localisation at both interfaces. No significant difference found between surface finishes in total gap area ((satin 3.1% ± 1.4):(grit 3.4% ± 1.5)), supporting our first hypothesis. S/c gap areas were significantly greater around grit blasted sections ((satin 0.1% ± 0.4):(grit 1.9% ± 1.7) p< 0.0001). C/b gap areas were significantly greater around satin finished sections ((satin 2.3% ± 1.3):(grit 1.0% ± 0.9) p< 0.0001), supporting our second hypothesis.

Shrinkage can localise into large interface gaps; which must lead to stress concentrations. C/b gaps are potentially benign as they can fill with bone. Cement failure at points of s/c contact would generate debris hindering bone formation.

There are multiple proximal prosthetic geometries available for a surgeon to select when humeral head replacement is indicated for four-part proximal humerus fractures. We compared different proximal prosthetic geometries in stable and unstable fracture patterns, with a standard tuberosity fixation method.

Simulated four-part fractures were created with an oscillating saw in six synthetic shoulder models. Three different proximal prosthetic geometries used polymetylmethacrelate (PMMA) – a smooth circular shape (SCS), a diamond shape (DS) and an irregular multiple fin shape (IMFS) prostheses. A standardised fixation method using vertical, and horizontal straps along with a medial based cerclage strap was performed. Passive motion was then carried out using a robotic articulator. Interfragmentary displacement was measured from tuberosity to tuberosity as well as tuberosity to shaft using mercury strain gauges.

The least amount of interfragmentary motion occurred when an IMFS was used in a stable fracture pattern. This geometry provided more interfragmentary stability even with the unstable fracture pattern than the DS or SCS. The least stable construct was the SCS prosthesis with an unstable fracture pattern.

Prosthetic geometry does affect stability of tuberosity reconstruction in proximal humerus fractures. An irregular shaped prosthesis augments the fixation construct. When using a smooth prosthetic design a stable fracture pattern must be achieved to prevent excessive interfragmentary motion. A smooth prosthetic design for tuberosity reconstruction is not recommended.

There is little information available regarding mechanical aspects of cemented implant loosening and the initiation and development of cement damage. Previous studies have come to a variety of conclusions about the development of cement damage and the relative importance of voids, the stem/cement interface and the cement/bone interface.

Cement micro-cracks and stem/bone micro-motions were quantified for Charnley Cobra stems under “stair-climbing” loads. Six stem/cement/femur constructs were subjected to loads based on estimated body weight for 300 kcycles at 2 Hz; two additional constructs were not loaded. Transverse sections were cut at 10 mm intervals, stained with a fluorescent dye penetrant and examined using epifluorescence stereo-microscopy.

Despite the aggressive loading, all stem/bone micro-motions were small and all stems were “well fixed” at the end of the loading. The only consistent micro-motion was internal rotation but this did not significantly correlate with cement damage (p=0.9). For cyclically loaded constructs mean crack length was 0.49 mm (SD 0.37, range 0.07 to 4.42) and for non-loaded controls mean crack length was 0.25 mm (SD 0.18, range 0.03 to 1.16). Total crack length (46–281 mm) was significantly correlated (R2=0.819, p=0.002) with femoral head load (0 & 1.0–1.8 kN). There was a significantly (p< 0.05) greater proportion of damage at the cement/bone interface (66% ± 9) than at the stem/cement interface (28% ± 8). A small fraction of micro-cracks involved voids (5% ± 5), but these were significantly (p< 0.001) less than the cement/ bone fraction. Micro-cracks in unloaded specimens were evenly distributed axially (R2=0.0002, p=0.95) consistent with the theory that they were induced by cement shrinkage. ANCOVA for total crack density using head load and axial position as covariates showed a significant positive effect for head load (p< 0.0001) and a significant interaction between head load and axial position (p=0.001); under load, micro-crack density increased proximally, and this effect was stronger with increasing head load.

A high proportion of complications following TKR occur at the patellofemoral articulation secondary to delami-nation and adhesive/abrasive wear. Electron beam cross-linking and melting has been shown to substantially reduce delamination and adhesive/abrasive wear in polyethylene tibial inserts. A series of in-vitro patella wear and fatigue tests were developed to explore the benefits of this material at the patellofemoral articulation.

Patellae (NKII, Sulzer Orthopedics, Inc., Austin, TX) were tested on an AMTI (Watertown, MA) knee simulator articulating against the trochlear grove of the femoral component. The simulator controlled flexion/ extension and patellofemoral contact force. Each test included patellae manufactured from conventional and electron beam crosslinked and melted polyethylene. Three different simulations were created: i) normal gait (5 million cycles) with optimal component alignment, ii) stair climbing (2 million cycles) with optimal component alignment, iii) stair climbing (2 million cycles) with 4° of femoral component internal rotation to simulate a component malalignment condition. In the last two simulations all patellae were artificially aged for 35 days in 80°C air to simulate one aspect of the long term oxidative state of each material.

In normal gait, the unaged conventional and highly cross-linked materials demonstrated similar behaviour. In stair climbing with optimal component alignment, the aged conventional patellae developed cracks by 2 million cycles. In stair climbing with component malalign-ment the aged conventional patellae developed cracks and delamination by 1 million cycles. None of the highly cross-linked components showed cracks or delamination. These results demonstrate the potential advantage of highly cross-linked polyethylene for the patella.

With the growing number of patients that are being treated with hip arthroplasty, the number of patients that require revision surgery is increasing as well. In clinical practice, the diagnosis of a loose hip prosthesis is, in addition of clinical evaluation and radiographic techniques, often made using scintigraphic techniques. However, with regard to the performance of these techniques, reported results have shown to be inconsistent or sometimes even contradict when assessing the acetabular component. Therefore, in order to evaluate the test performance and efficacy of radiographic and scintigraphic techniques in the evaluation of patients suspected of aseptic loosening of acetabular components, we conducted a systematic review and meta-analysis of clinical studies.

In order to identify all studies that examined the use of radiographic or scintigraphic techniques in the evaluation of aseptic loosening of the acetabular component, we used systematic methods to identify English-language published papers and human-adult studies published between January 1975 and December 2001. Using a modified checklist, designed by the Cochrane Methods Group on Systematic Review of Screening and Diagnostic Tests, a quality analysis was performed by two independent reviewers.

There were 18 studies (n=1026) analysing the performance of plain radiography, 24 studies (n=825) regarding contrast arthrography, five studies (n=203) describing the performance of nuclear arthrography and 15 studies (n=549) regarding bone scintigraphy. Pooled sensitivity for plain radiography was 77% (spec. 82%), contrast arthrography revealed a sensitivity of 82% ( spec. 73%), nuclear arthrography 82% (spec.58%) and bone scintig-raphy 70% (spec.73%).

Pooled sensitivity and specificity showed that plain radiography, due to the high specificity, appears to be the technique of first choice in the assessment of patients suspected of aseptic loosening of a acetabular component, followed by contrast arthrography, due its higher specificity compared with nuclear arthrography. However, the methodological quality of the majority available studies was limited.

Correct alignment is important for success in total knee replacement. Currently this is achieved by a combination of intramedullary and extramedullary alignment using jigs and cutting blocks. This multicentre study evaluates the use of computer assisted planning and the interactive guidance of instruments for total knee replacement.

Prior to surgery computer scans of the hip, knee and ankle were performed of patients enrolled in the study. Pre operative planning of the position and size of the knee components was performed by the surgeon using a CT based Vector Vision Navigation System (Brain LAB AG, Heimstetten, Germany). P.F.C.x (De Puy Leeds UK) knee replacements were then implanted in 38 patients. Surgery was carried out according to the standard surgical technique using traditional instruments. Information of the planned and intraoperatively recorded position of the cutting blocks were analysed to check varus/valgus alignment, flexion/extension alignment, the amount of planned resection from both the femoral and tibial bones and the size of the components. Information from all the separate centres was sent to a central data processing base for analysis.

Results were calculated comparing the differences between the planned and performed cuts for each of the different variables studied. Graphs demonstrate the differences in the alignment between that planned by the surgical navigation system and what was actually carried out by the instrumented cuts.

Based on the data obtained from the multicentre study we have concluded that the planned position of the implants using the standard instruments was similar to that using the Vector Vision Navigation System. We believe that it is safe to proceed with surgical navigation total knee arthroplasty using the P.F.C.x total knee prosthesis with Image Guided Surgery and a further multicentre study is currently underway evaluating this.

There are many previous reports dealing with the relationship between the abductor moment arm or femoral offset (FO), and other factors such as the abductor muscle strength after total hip arthroplasty (THA). Moreover, there have been no studies involving quantitative examination of the influence of posterolateral reconstruction on abductor muscle strength and FO. This study was to evaluate posterolateral reconstruction including posterior capsule, piriformis tendon and external rotators in THA and the relationship among the posterolateral reconstruction, abductor muscle strength, and FO.

We arbitrarily selected 48 limbs of 24 patients who underwent unilateral THA using a posterolateral approach. In 16 patients (12 women and 4 men; mean age, 66.8 years; range 50 to 82 years), posterolateral reconstruction was not performed (non- reconstruction group). In eight patients (6 women and 2 men; mean age, 61.6 years; range 52 to 72 years), posterolateral reconstruction was performed (reconstruction group). None of the selected cases were revision cases, cases in which the patient showed marked acetabular dysplasia, or cases involving the osteotomy of the greater trochanter. We compared these two groups. FO was measured on standard antero-posterior hip radiographs. Isometric abductor muscle (N) was measured with hand-held dynamometer. Each muscle strength was converted into a ratio of force to body weight (N/kg), and this ratio was used for comparison.

The reconstruction group showed higher value than the non-reconstruction group on the abductor muscle strength (p< 0.05). The correlation was recognised in the reconstruction group between abductor muscle strength and FO (p< 0.01 r=0.68).

There have been no studies involving quantitative examination of the influence of posterolateral reconstruction on abductor muscle strength and FO. Our results suggested that posterolateral reconstruction and appropriate reconstruction of FO were important in order to obtain the improvement on the abductor muscle strength after THA.

According to the knee simulator test results in 1970s, the total decrease in thickness of UHMWPE tibial tray in combination with ceramic femoral component [F-Comp] was less than one tenth as that of the combination with metal [1]. These advantages led to development of total knee prosthesis [TKP] with alumina ceramics. In this study, we report the wear surface observation, the clinical wear and the oxidation of the retrieved TKP used clinically for 23 years, comparing with a metal TKP.

The retrieved TKP was implanted in 1979, and retrieved on January 9th in 2002. This TKP consisted of an alumina ceramic F-Comp and a UHMWPE tray combined with a alumina ceramic tibial component. Observations of the surface of alumina F-Comp and UHMWPE tray were carried out using SEM. Shape of UHMWPE tray was determined three-dimensionally. Comparing the result with original shape based on the product’s plan, liner wear and volumetric wear were calculated. Oxidation index was determined by Fourier transform infrared spectrophotometry.

Alumina F-Comp did not have any scratch on the surface by seeing with naked eye. UHMWPE tray had deformation and scratches obviously. The liner wear rate was 37 micrometer/year and volumetric wear rate was 18.8 mm3/year. The oxidation indexes were 0.6 in the unworn area, 1.2 in the worn area and 0.2 in the inner area.

SEM observations of the F-Comp demonstrated no scratch or pit. In contrast, many scratches were clearly observed on the UHMWPE tray. However, higher magnification observations did not demonstrate severe wear, which was shown on the wear analysis of a metallic F-Comp. Oxidation degradation is a problem to solve. However, the low wear rate and mild wear pattern demonstrate that ceramic F-Comp reduced UHMWPE wear.

In clinical studies of cemented total hip arthroplasty (THA), polished stems produce less slippage at the bone-cement interface than roughened stems. Our objective is to assess the effect of stem-cement debonding on the bone-cement interface shear behaviour of hip implants using simplified axisymmetric stem-cement-aluminum models.

We emulated the femoral stems using stainless steel tapered plugs with either a rough (i.e. bonded) or smooth (i.e. unbonded) surface finish. Three different taper angles (5°, 7.5°, 10°) were used for the unbonded constructs. Non-tapered and tapered (7.5°) aluminum shells were used to emulate the diaphyseal and metaphyseal segments of the femur. In all cases, the cement-aluminum interface was designed to have the same shear strength as has been reported for bone-cement interfaces (~8 MPa). The test involved applying axial compressive loading at a rate of 0.02 mm/s until failure. Six specimens were tested for each combination of the parameters.

The unbonded stems sustained about twice as much load as the bonded stem, regardless of taper angle, and the metaphyseal model carried 35-50% greater loads than the diaphyseal models before shear failure or slippage. The unbonded constructs reached peak load with excessive displacement due to creep of the cement mantle while the bonded constructs failed in shear at the cement-aluminum interface. This result supports the hypothesis that the wedging forces created in the unbonded construct increase the compression forces across the aluminum-cement interface, thereby increasing its shear resistance. A finite element analysis predicted that the cement could withstand the hoop stress under these loading circumstances and this prediction was confirmed by visual inspection of the cement after each test.

Our results suggest that smooth or unbonded stems should sustain less slippage and shear damage at the bone-cement interface than roughened or bonded stems due to the wedge-induced compressive stress; this increased load capacity will be particularly valuable when the condition of the bone-cement interface is suboptimal.

This comparative clinical and radiographic study evaluates the role of implant design and positioning on maximum postoperative flexion after TKR.

Two groups of cemented posterostabilised mobile prosthesis were studied. In group A (23 cases) bearing mobility was possible in rotation and translation. In group B (36 cases) solely rotation was possible and the radius of the posterior femoral condyle was larger. In both groups the same medial transquadricipital approach was used and the postoperative rehabilitation was identical.

There were no significant difference between the two groups for patient age, sex, weight and etiology. The average preoperative flexion was 120.8° in group A and 120.7° in group B. The average postoperative flexion at one year was 114.8° in group A and 130.4° in group B. Instability was noted twice in group A and none in group B. Radiographically there was no difference in mechanical axis or patellar height. There was a difference in joint line elevation and anteroposterior joint size.

Higher flexion angle may be related to smaller antero-posterior joint size, better posterior osteophytes removal and larger posterior femoral condyle radius. Greater stability correlates with greater jumping distance over the tibial post. This study showed that deep flexion can be achieved in some patients after TKR, with implications on surgical technique and implant design.

After experimental and preclinical evaluation (HAP Paul Award 2001) of a CT-free image guided surgical navigation system for acetabular cup placement, the system was introduced into clinical routine. The computation of the angular orientation of the cup is based on reference coordinates from the anterior pelvic plane concept. A hybrid strategy for pelvic landmark acquisition has been introduced involving percutaneous pointer-based digitisation with the non-invasive bi-planar landmark reconstruction using multiple registered fluoroscopy images.

From January 2001 to May 2002 a total of 118 consecutive patients (mean age 68 years, 82 male, 36 female, 62 left and 56 right hip joints) were operated on with the hybrid CT-free navigation system. During each operation the angular orientation of the inserted implant was recorded.

To determine the placement accuracy of the acetabular components the first 50 consecutive patients underwent a CT scan seven to ten days postoperatively to analyse the cup position related to the anterior pelvic plane. This was done blinded with commercial planning software. There was no significant learning curve observed for the use of the system.

Mean values for postoperative inclination read 43° (SD 3.0, range 37 to 49) and anteversion 19° (SD 3.9, range 10 to 28). The resulting system accuracy, i.e., the difference between intraoperatively calculated cup orientation and postoperatively measured implant position shows a maximum error of 5° for the inclination (mean 1.5°, SD 1.1) and 6° for the anteversion (mean 2.4°, SD 1.3).

An accuracy of better than 5° inclination and 6° ante-version was achieved under clinical conditions, which implies that there is no significant difference in performance from the established CT-based navigation methods. Image guided CT-free cup navigation provides a reliable solution for future THA.

Hip resurfacing is widely recognised as a bone conserving procedure with respect to proximal femoral resection. However, it has been argued that this is not the case for the acetabulum due to the thickness of the acetabular component and the large diameter bearing surfaces. We have investigated whether the Birmingham Hip is a bone conserving procedure with respect to the acetabular bone stock.

Data was obtained from 257 consecutive Midland Medical Technology (MMT) surface replacements and 458 primary hybrid total hip replacements implanted under our care. The surface replacement group comprised 185 males (185 hips) and 72 females (72 hips) with a mean age at surgery of 55 years. The hybrid primary total hip replacement group comprised 207 males (207) and 251 females (251 hips). The mean age at surgery was 65 years old. In the surface replacement group the mean uncemented acetabular size implanted was 54.88 mm (females = 51.9 mm; males = 57.8 mm). In the hybrid primary total hip replacement group the mean uncemented acetabular size of 55.04 mm (females =52.9 mm; males = 57.2 mm).

Statistical analysis was undertaken to compare the uncemented acetabular sizes in the surface replacement group with the uncemented acetabular sizes implanted in the primary hybrid total hip replacement group. We report no significant difference in the size of acetabular component used for the two groups (p = 0.4629; 95% C.I. −0.28 to 0.61). The effect of gender was analysed and the mean size of uncemented acetabular component implanted in males for the surface replacement group was not significantly different (p = 0.06) to the hybrid primary total hip replacement group. However the mean size of uncemented acetabular component in females for the surface replacement group was significantly smaller (p = 0.016) compared to the primary total hip replacement group.

We conclude hip resurfacing is not bone sacrificing on the acetabular bone stock and can be bone conserving for females.

The use of porous ceramics as bone graft substitutes (BGS) has been under consideration for over 30 years [1]. In particular calcium phosphates such as hydroxyapatite (HA) have been promoted as a result of their osteoconductive properties, i.e. that they stimulate bone apposition within their macroporous structures.

It is well established that both pore size [1] and pore connectivity [2] are critical morphological elements for a successful BGS. Thus biologically ‘optimal’ structures, with relatively large levels of porosity (> 70%) are consequently low in mechanical strength, with typical UCS values of between 1–8 MPa depending on the precise level of porosity and the pore size distribution. The aim of this investigation was to study the biological response to a porous HA with a relatively low level of macro-porosity (64%), but which possessed a highly interconnected micro-pore structure within the HA struts.

Phase pure porous HA implants were manufactured using a novel technique [3] with a mean macro-pore size of 230 ìm and a mean pore interconnection size of 110 μm. Cylindrical specimens 4.5 mm in diameter were implanted in the distal femur of 6 month New Zealand White rabbits and retrieved for histological and histomorphometric analysis at 4 weeks. The mineral apposition rate (MAR) was determined through the administration of fluorochrome labels at 1, 2 and 3 weeks.

After 4 weeks new bone had penetrated deep within the macro-pore structure and at high magnification osteocyte-like cells were observed occupying micro-pores within the ceramic struts. Furthermore, there was a significant increase in the MAR of bone formed within and surrounding the PHA (5.21 ìm.day-1, 4.42 ìm.day-1) as compared to the normal turnover rate of control bone (2.07 ìm.day-1, 2.09 ìm.day-1) during weeks 1-2 and 2–3, respectively.

The micro-porous network within the scaffold struts clearly influenced the host response. This could be linked to an associated increase in roughness or surface area, or it may reflect the greater level of strut permeability underlining the importance of nutrient transfer and the promotion of angiogenesis in scaffolds for bone repair.

With 3D CT data of proximal femora it is possible to develop a computer programme for optimising femoral component fit and simulation of implantation. The implantation of the femoral stem can be simulated with any femoral component that has cortical press fit.

Five different currently used femoral components were virtually “implanted” in over 200 different femoral bone data. Optimal femoral fit was defined, when the component showed best diaphyseal and metaphyseal congruent contact with all CT data available. Position of neck and head were secondary, since an optimal press fit situation had priority in our set-up. Best fit was considered taken cortical contact and reconstruction of joint geometry into account.

There were numerous failures in all tested standard components, when correct angle of antetorsion, off-set, and leg length were expected. There were considerably better results with the use of CTX standard prosthesis (CTX-S).

The data of this study indicate a high proportion of less optimal fit with femoral standard components tested in this series. Indication for choosing CTX-S femoral components is dependent upon the individual geometry of dysplastic hip joint and the simulation results of standard components using the VIP method.

Highly polished femoral stems with a double taper have had outstanding long-term clinical results. Recently a stem with a third, cross-sectional taper was introduced with the goal of providing additional stability while still utilising the polished taper concept.

The goal of the present study was to determine if there were differences in the mechanical stability and cement damage due to cyclic loading of a triple-tapered (C-stem, J& J-DePuy) and a double-tapered design (TPS, J& J-DePuy). Six pairs of cadaveric femurs were cemented with either C-stem or TPS stems using contemporary techniques. Specimens were cyclically loaded using a stair-climbing apparatus with femoral head and abductor loads for 1 000 to 266 000 loading cycles. Motion between the stem and bone was measured using a 6 dof measurement system. Following testing, specimens were sectioned at four transverse levels and the number and length of cracks in the cement were measured.

All stems were extremely well fixed after loading. The C-stem did not subside during loading except for one outlier that was cemented ‘high’. The TPS stem had a pattern of rapid subsidence over the first 100 cycles (mean 0.032 mm) followed by a more gradual subsidence (0.05 mm at 266 k cycles). ANCOVA showed that the TPS-stems rotated significantly more than the C-stems (p< 0.0001), that the rotation of both stems increased with number of loading cycles (p=0.022) and that the effect of number of loading cycles was greater for the TPS stems (p=0.047). Total crack length was not a function of number of loading cycles, nor was it different for the two stem designs (p=0.33).

The outlier C-stem had micromotion behavior similar to the TPS stem. The reason for this is unclear, but could be due to reduced lateral-proximal cement. Thus it is possible that both the stem cross-sectional and in-plane shape contribute to the stability of the C-stem design.

Proper pre-clinical testing of cemented THA implants may help to prevent bad implants from entering the market. Within the frame of a multinational EU-program, a finite element (FE) simulation was developed, for FE-based pre-clinical testing of cemented THA stems against the damage accumulation failure scenario. The simulation allows monitoring of cement crack formation and implant migration in cemented THA reconstructions. The current study is concerned with the clinical validation of the test. The damage accumulation failure scenario was simulated for four cemented hip stems, with well-known survival rates. The question was: Can the FE simulation rank the stems according to their clinical survival rates?

Four stems were analysed: the Lubinus SPII, the Exeter, the Charnley and the Mueller Curved. The Swedish hip register [1] reports survival rates of 4, 5, 8 and 13%, respectively, at 10 years after surgery. Four FE models were created, representing cemented THA reconstructions with the four stems in composite femurs. The stem-cement interfaces were unbonded (m = 0.25). A loading history was applied to the models, representing 20 million cycles of alternating walking and stair climbing. Using a 3D continuum damage mechanics approach, the damage accumulation and creep processes in the cement, and subsequent prosthetic migration were monitored.

The Mueller C. produced a considerably higher number of cement cracks than the other three stems. Cracks were formed around the entire stem. The cracked zones often extended over the thickness of the mantle. The Charnley performed better, with a lower number of cracks. Proximo-distal damage pathways were formed, although at a much lower rate than around the Mueller C. The Exeter performed better. Full thickness crack zones were produced only in the proximo-medial region. The Lubinus performed best, with the lowest number of cement cracks. No full thickness cracks were formed. Concerning migration, the Exeter migrated more than the other stems. From the collared implants, the Lubinus SPII showed the lowest migration values.

When considering the number of cement cracks produced in the simulation, the ranking of the stems would be, from superior to inferior: Lubinus SPII, Exeter, Charnley, Mueller Curved. This ranking corresponds to a ranking based on clinical survival rates. The stems behaved according to their design concepts, with the highest migration values for the Exeter stem. In conclusion, the FE simulations produced a clinically valid ranking of four cemented THA implants. This corroborates the use of the FE simulation for pre-clinical testing purposes.

The new 3-Dimensional (3D) polyethylene wear measurement software GAWDI (Genetic Algorithm for Wear Detect Instrument) was developed to evaluate in vivo movement of the femoral head into the polyethylene liner. It enabled to detect 3D position of femoral head against polyethylene socket from two radiographs. Inter observer error of this system was 0.09 mm, intra observer error was 0.08 mm. Fifteen patients after THA was taken anterior-posterior (AP) and semi-lateral radiographs in both standing and supine position one year post operation. The difference of the 3D position of the femoral head was not observed between standing and supine position. However 8.1 degrees (mean) and 0.2 to 16.5 degrees (range) pelvic tilt was observed between these positions. 0.8 mm (mean) difference was observed by 2-Dimensional measurement system although no difference was observed by 3D system. Small separation between head and socket was observed in a few patients. However the influence of pelvic tilt was main origin of the difference between 2D and 3D measurement methods.

The indications for unicompartmental knee arthroplasty (UKA) can be contentious. Concerns exist about implanting a UKA in younger individuals. It has been reported that it is contra-indicated in patients under the age of 60. The suggestion is that younger patients may compromise their outcome after surgery by their increased activity levels. However, the number of publications with data on UKA in young patients is minimal and the age/activity related criteria for UKA remains unknown.

The aim of the study was 1) to confirm that younger UKA patients have higher activity levels than older patients, and 2) to test the hypothesis that younger, more active patients have inferior outcome when compared to older less active patients.

Fifty consecutive patients undergoing UKA who were under 60 years (Group Y) and 50 patients over 60 years (Group O) were recruited. Indications were anteromedial arthritis with full thickness lateral compartment cartilage, a functioning ACL and a correctible varus. All patients underwent Oxford UKA using the minimally invasive technique. This device employs an unconstrained fully congruous meniscal bearing. Outcome was evaluated using Knee Society Scores. Activity level was documented using Tegner Activity Score.

Average age of patients for group Y and O was 55 and 68 years respectively. Minimum follw-up was 2 years. pre-op. knee scores were comparable for each group. (y: 38.8, O: 35.8) and patients in both groups siginificantly improved after surgery. A significant difference in Tegner score was found between the two groups after surgery (y:4.1, O:2.6). More than 50% of younger patients regularly participated in high demand activities like skiing, tennis and manual labour. No statistically significant differences in any other post op. knee scores or complication rate were found despite adequate study power.

Younger patients have increased activity levels after UKA when compared to an older age group. There is no evidence that the outcome of UKA in younger more active patients will be inferior to those who are older and more sedentary.

The disadvantages of sawing for precise bone cuts are well known: untrue cuts, heat and metal wear. The main limiting factors of available milling devices are the difficult handling and high costs, especially if the devices are based on a robot. Supported by clinical users and mechanical engineers a milling concept adopted from industrial machining has been realised in order to overcome this limitations. The “All-in-One Milling-Tool” achieves the same precision of a robot by a mechanically guided milling resection far below the necessary investment for a robot. Once fixed at the femur, the device allows all femural and tibial resections. Three methods are provided for the alignment of the resection planes and will be discussed: intramedullary adjustment, 3D CT-based planning and intramedullar performance as well as the performance under navigation control. All versions are based on a handheld resection and guarantee a visual and haptical feedback for the surgeon. The use of navigation has the advantage of the accurate transfer of the 3D plan into the OR, the interactive guided and facilitated alignment und resection steps and the documentation of planned and actual implant position.

We analysed periprosthetic bone mineral density (BMD) by dual-energy X-ray absorptiometry (DEXA) in patients after uncemented total hip arthroplasty (THA) (press-fit CLS Spotorno stem). Only patients with good clinical outcome (Merle d‘ Aubigne score > 12) were included to obtain normative data for regular bone response.

Two separate studies were performed: A prospective longitudinal study over a time period of 7 years (group A) (n = 26 patients: 12 women, 14 men) and an additional cross-sectional study, mean follow-up13 years (10 to 15 years) (group B) (n = 35 patients: 18 women, 17 men). Regions of interest were defined according to Gruen (ROI 1–7) and as netto average ROI (NETAVG) for the periprosthetic femoral bone. After the initial remodelling process, BMD at 1 year was compared to the 7-year (longitidinal) and to the 13-year (cross-sectional) follow-up values of the affected limb to determine long term periprosthetic changes of bone mineral density.

The longitudinal study (group A) showed BMD values of 91.1% and 92.8% after 1 year, 91.2% and 90.2% after 7 years compared to the initial post-operative values for women and men, respectively. ROIs around the proximal stem (ROI 1 and 7) showed the lowest absolute values and decreased most during follow-up (ROI 1: 80.7% and 84.5%, ROI 7: 71.1% and 75.5% after 7 years, for women and men respectively). In the cross-sectional study (group B) BMD was determined 89.1% and 87.8% after 13 years compared to the initial values of group A for women and men. Distribution of BMD in ROIs 1-7 (group B) showed no significant changes compared to the 1 year and 7 year results of group A. The results reflect normative long term changes in the periprosthetic bone after implantation of THA in defined ROIs of a well functioning tapered corundum-blasted titanium stem.

CT-based, customised femoral stem enables optimal reconstruction of hip mechanics and leg length. However, traditional planning and execution of cup insertion may jeopardise these biomechanical parameters. The aim of this study was to examine the agreement of the preoperative planning of cup position and the final position of the cup.

Thirty total hip replacements with an uncemented acetabular cup (Duraloc, DePuy) or a cemented cup (Elite-Plus, DePuy) were included. A customised femoral stem was used in all hips. On the preoperative X-rays the planned position and orientation of the cup had been marked prior to the surgery. The pre- and postoperative X-ray images were then digitised and scaled. The planned and final positions of the cup centre in the frontal plane was then measured relative to a horizontal line defined by the tear-drops and to a vertical line through the centre of the tear-drop on the operated side. In addition the concurrence between the planned and final cup size was examined.

In the horizontal direction the cups were positioned 1.4 (7.6) mm (median, ±2SD) more medial than planned on the preoperative X-rays. In the vertical direction the corresponding figures were 1.2 (6.6) mm (median, ±2SD) and the cups were usually placed more cranially than was planned. The maximum discrepancy between the planned and final position was 10,6 mm in the horizontal direction (medial) and 7.1 mm in the vertical direction (cranial). In 63% of the hips there was agreement between the size of the cup planned preoperatively and the cup that was finally inserted. In 25% of the hips the final cup was larger and in 12% the final cup was smaller.

In most cases the acetabular cups were inserted within a few millimetres of the planned position. The combination of a standard uncemented or cemented cup with a custom femoral stem enables the surgeon to restore hip mechanics and leg length.

The wrist is arguably the most complex joint in the body and is essential for optimal hand function. The joint may be represented as two roughly orthogonal hinge axes, providing flexion-extension and radial-ulnar deviation. The location and orientation of these axes with respect to the underlying anatomy is essential for the design of successful joint prostheses. A population study was performed in order to obtain the parameters of this two-hinge joint.

Data for 108 normal right wrists was gathered using a Fastrak electrogoniometer with sensors fixed to the distal medial radial styloid and the distal third metacarpal head. Data was recorded as a series of three-dimensional coordinates covering the entire locus of movement.

The two-hinge geometry of the joint was represented mathematically with nine parameters describing the configuration of the axes and two angles controlling rotation about these axes. The configuration giving the closest kinematic match to the experimental data was determined using two nested optimisation processes. During the inner optimisation process, the third metacarpal head was brought as close as possible to each of the experimental points in turn by adjusting the two positioning angles. The sum of distances from each experimental point to the point of closest approach gave the “cost” of the current configuration. The outer optimisation process repeated the inner process iteratively, minimising the cost by adjusting the nine configuration parameters.

The double optimisation method was found to offer an innovative solution to the problem of analysing kinematic data from a population study. The mean joint configuration showed the axis of radial-ulnar deviation to be 1.9 mm (sd = 12.5 mm), distal to the flexion-extension axis, with axes almost orthogonal to one another. This data together with the radii of the rotations is invaluable in determining the optimal articulation geometries for wrist joint replacement prostheses.

To determine the precision of conventional versus computer assisted techniques for positioning the acetabular component in total hip arthroplasty (THA).

Malposition of the acetabular component during THA increases the occurrence of impingement, reduces range of motion, and increases the risk of dislocation and long-term wear. To prevent malpositioned hip implants, an increasing number of computer assisted surgery systems have been described, but their accuracy is not well established.

Using a lateral approach, 150 cups were placed by 10 different surgeons in 10 identical plastic pelvis models. Only the immediate operating field was visible. Pre-operative planning was performed with a computerised tomography scan. Fifty cups were placed free hand, 50 others with the standard cup positioner, and the remaining 50 cups using computer-assisted orthopaedic surgery (Medivision). The accuracy of cup abduction and anteversion was assessed with an electromagnetic system (Fastrak™).

Using conventional techniques, free hand placement revealed a mean precision of cup anteversion and abduction of 10° (range 5.5 to 14) and 3.5° (2.5 to 5) respectively. With the cup positioner, these angles measured 8° (5 to 10.5) and 4° (3 to 5.5) respectively, and using the computer assisted method, the mean cup anteversion precision was 1.5° (1 to 2) and mean cup abduction measured 2.5° (2 to 3.5).

Computer assisted cup placement is a very accurate and reproducible technique during THA. It is clearly more precise than either of the two traditional methods of cup positioning, even for well-trained surgeons.

Modular knee bearings typically consist of a femoral component, a tibial base-plate and a polyethylene insert, which is located in the tibial base-plate using some sort of locking mechanism. Although modular knee bearings offer many advantages there is the potential for micro-motion between the tibial insert and the base-plate.

Tests were performed on six large Kinemax Plus knee bearings (snap-fit design) to evaluate the amount of movement between the tibial inserts and the tibial base-plates. The knee bearings were tested up to one million cycles on the Durham Six-Station Knee Wear Simulator which subjected the bearings to similar motion and loading profiles that would be experienced by the natural knee during walking. The movement of the tibial inserts was measured with dial gauges (accuracy of ±0.01 mm) before and after the bearings were tested on the simulator, when unloaded, and throughout the tests whilst the bearings were being dynamically loaded in the simulator. Movement occurred between the tibial insert and the tibial base-plate after initial assembly due to the snap-fit mechanism used to locate the tibial insert within the tibial base-plate. However, this decreased appreciably when the bearings were loaded in the simulator. The amount of movement did not change with time when the bearings were continuously loaded in the simulator. However, after each test the amount of movement of the tibial inserts, when unloaded, was less than before the test. This was thought to be due to creep of the UHMWPE inserts. The movement between the tibial insert and tibial base-plate in-situ is likely to be much less than that observed by a surgeon at the time of assembly due to loading of the knee bearing in the body. However, the amount of movement when the tibial inserts are loaded may still be great enough to produce a second interface where wear of the tibial insert may take place.

To measure micromotion of an orthopaedic implant with respect to its surrounding bone, Roentgen Stereo-photogrammetric Analysis (RSA) was developed. A disadvantage of conventional RSA is that it requires the implant to be marked with tantalum beads. This disadvantage can potentially be resolved with model-based RSA, whereby a 3D model of the implant is used for matching with the actual images and the assessment of position and rotation of the implant. In this study, an improved model-based RSA algorithm is presented and validated in phantom experiments. This algorithm is capable to process projection contours that contain drop-outs. To investigate the influence of the accuracy of the implant models that were used for model-based RSA, we studied both Computer Aided Design (CAD) models as well as models obtained by means of Reversed Engineering (RE) of the actual implant.

The results demonstrate that the RE-models provide more accurate results than the CAD models. If these RE models are derived from the very same implant, it is possible to achieve a maximum standard deviation of the error in the migration calculation of 0.06 mm for translations in x- and y-direction and 0.14 mm for the out of plane z-direction, respectively. For rotations about the y-axis, the standard deviation was about 0.1 degree and for rotations about the x- and z-axis 0.05 degree. For the femur component, it was also possible to reach these accurate results for non-scanned components. The results show that the new algorithm is an improvement with respect to a study we presented earlier [1].

Studies with clinical RSA-radiographs must prove that these results can also be reached in a clinical setting, making model-based RSA a possible alternative for marker-based RSA.

The aim of the study was to evaluate THA using Robodoc system for osteoarthritis of the hip joint.

The Robodoc system consists of: 1. the Orthodoc computer workstation that simultaneously displays computerised tomography images of patient’s femur and a selected prosthesis, 2.a five-axis robot, 3.the operating room display, 4. the control cabinet.

Follow up were 3months and 1 year on 27cases (Male 5, Female 22). Selected stems: Zimmer anatomic, 13, Versis 14(VSS,7, VSL,7). Mean age 57.9. Among 27 cases of osteoarthritis, one is after osteotomy and two are after osteonecrosis. Pain, ROM, Radiographs and ADL were evaluated using JOA hip score system. Sockets were fixed with cementless conventional technique.

Mean operating time, 2 hours and 40min.; Mean bleeding, 455 ml; Mean Ant. Version, 29.26 degree (22.0–39.7); Level of osteotomy of the femur neck, Mean, 9.19 mm from the trochanter minor. JOA hip score after THA, 82.20. In one case, 5 mm sinking occurred 5 days after the operation. No intraoperative femoral fractures and varus or valgus insertion of stems occurred in 27cases. The thigh pains were nothing. The patients were discharged at 4weeks after the operation with one crutch. The results showed statistically better fit and fill of the femoral component in the Robodoc system.

The Robodoc system is thought to be safe and effective in producing radiographically superior implant fit and positioning without fractures and other complication. Precise fit of the implant may be increase bone-to-implant contact, providing stress transfer from prosthesis to bone and more bone growth into prosthesis.

Kneeling is an important aspect of daily living. Our goal was to describe the in vivo tibiofemoral kinematics during standing and kneeling after total knee arthroplasty (TKA).

Ten posterior substituting (PS) and 10 cruciate retaining (CR) TKA designs were studied in 18 patients. Radiographs were taken when standing, kneeling at 90°, and kneeling at maximal flexion. An image matching technique provided three-dimensional measurements of the femoral component position relative to the AP midpoint of the tibial baseplate.

When standing, the CR tibiofemoral contact position (medial: 7 mm ± 3; lateral: 6 mm ± 3) was more posterior than the PS design (medial: 5 mm ± 2; lateral: 5 mm ± 2). Movement from standing to kneeling at 90° produced different responses. CR knees translated anteriorly (medial: 4 mm ± 4; lateral: 2 mm ± 6), while PS knees translated posteriorly (medial: 0.2 mm ± 3; lateral: 1 mm ± 4). During kneeling, movement from 90° to maximum flexion produced posterior translation of the femur (CR medial: 5 mm ± 4: CR lateral: 5 mm ± 4; PS medial: 6 mm ± 4; PS lateral: 6 mm ± 3). The relationship between the tibiofemoral contact position and flexion angle during kneeling was more variable for CR knees (r2=0.38) than PS knees (r2=0.64), indicating that PS knees provide a more reliable AP position than CR knees.

PS knees dislocate when the arch of the femoral cam slides over the tibial post; CR knees sublux when the femoral contact position translates beyond the edge of the tibial baseplate. The distance to dislocation averaged 13 mm ± 2 for PS knees, and 20 mm±4 for CR knees.

Many patients wish to resume normal activities, including kneeling after TKA. This study provides information for surgeons and patients considering kneeling after TKA.

The effect of pre-operative pain, physical function, mental function and multiple patient factors on patient outcome following TKR was examined.

After informed consent, 105 patients undergoing primary TKR completed preoperative SF-36 and WOMAC questionnaires and a Knee Society Score (KSS) was determined. These scores were repeated at 12 months. Patient data studied included age, gender, BMI and significant comorbid conditions such as diabetes, cardiac disease, and COPD. Statistical analysis included a univariate analysis, followed by a bivariate analysis and multiple regression analysis.

All physical dimensions of the SF-36, WOMAC and KSS showed highly significant improvements after one year. The KSS improved to a mean of 94.8 (p< 0.000001). For patients greater than 65 years of age, postoperative physical function was returned to normative scores for age matched controls. For patients less than 65, physical function did not reach age matched controls even though similar improvements in physical function were seen. Patients with lower physical function scores (PCS) pre-operatively showed greater improvement postoperatively yet did not reach the same absolute level of function as patients who had higher preoperative physical function. The mean PCS for men increased from 35 to 42, while for women it increased from 29 to 42 (p=0.042). Preoperative mental function (MCS) was a strong predictor of postoperative physical function. Patients with low preoperative MCS and one or more comorbid conditions were 10.1 times more likely to have a poor outcome following TKR.

Knowledge of preoperative physical function, mental function, gender, age and comorbid conditions improves prediction of post-operative physical function after TKR. Patients at high risk for little improvement following TKR are those with low preoperative mental function (MCS< 50) in addition to one or more comorbid conditions. These patients can be identified during the pre-operative period.

Aseptic loosening is one of the most frequent cause of total knee arthroplasty (TKA) failure; it is related to a fatigue-type wear which can rapidly break up a tibial polyethylene (PE) inlay. PE debris production is the result of this wear and depend on contact stress between the components. This crucial parameter is more related to conformity than to load tranfer. That is why mobile bearing TKA seems to represent a valid solution to the PE debris production. In fact this implant offers great tibio-femoral conformity without an increased risk of loosening due to increased axial torque. Mobile bearing TKA also eneables the surgeon to self correct tibial component malrotation. On the other hand this implant could lead to new problems such as bearing dislocation or breakage and a possible new wear pattern at the PE-tibial metal tray interface.

We performed 100 consecutive cemented posterior stabilised TKA using randomly in 50 cases a mobile bearing and in 50 cases the same implant with a fixed bearing. The mean follow up was 15 months. The results in mobile bearing group are the following. Hospital for Special Surgery (HSS) score improved from 38 to 91 after the surgery. Preoperative Range of Movement (ROM) was 71 while the post op value was 107. No lucencies > 1 mm were observed. There were no statistically significant differences among the mobile bearing group and the fixed bearing one. Despite our short follow up, this implant offers the same good clinical results if compared to other devices, and allows the surgeons to correct errors in positioning the implant.

In future we have to consider that this possibility will lead to an abnormal load stresses distribution and to a higher risk of late loosening.

Massive bone replacing endoprostheses have become a well-recognised option in reconstruction of massive bone defects following tumor resections of the humerus, femur and proximal tibia. While the design of such bone replacements is somewhat standardised, massive endo-prosthetic replacements of the proximal radius have not been described. Previous work with radial head replacements for arthritis and fracture indications has been performed, but a massive replacement of the proximal radius has not been reported. The design for such a prosthesis has not been described. Herein, we present our initial case with a massive custom proximal radius replacement, and the incorporated design features.

A 43 year old gentleman presented with progressive destruction of the proximal right radius from meta-static renal cell carcinoma despite radiation treatment. His systemic disease was under satisfactory control. He had undergone a nephrectomy (37 months previously), hip replacement for metastatic disease (28 months previously) and internal fixation of a humerus fracture (10 months previously). Prior treatment of his radius included cast immobilisation and radiation treatment of a pathologic fracture 13 months preoperatively. He refractured his partially healed pathologic fracture two weeks prior to presentation. Following staging with CT and MRI scan, a custom proximal radius endoprosthe-sis was designed that replaced 13 cm of the proximal radius. It was designed with 6 degrees of radial bow. The design specifics will be presented during the presentation. Surgical technique will be demonstrated. By one month postoperatively, his elbow range of motion was from 10 degrees to 140 degrees of flexion, with 90 degrees each of supination and pronation. He continued to have excellent use of his arm until he developed brain metastasis 10 months postoperatively.

Massive custom proximal radius endoprostheses of this design may be useful in the reconstruction of meta-static and primary tumors of the forearm. They are compatible with preservation of motion, and may provide additional stability to the elbow in patients whom soft tissue may be compromised due to tissue destruction or tissue loss secondary to neoplasia.

We present the rationale and design of the DynaPort KneeTest. The test aims at measuring knee patients’ functional abilities in an unobtrusive, user-friendly way. Test persons wear several belts around their trunk and legs. The belts contain accelerometers, the signals of which are stored in a recorder, embedded in one of the belts. The knee test consists of a set of 29 tasks related to activities of daily life (“test items”). Accelerometer signals are analysed in terms of 30 “movement features” (accelerations, angles, durations, frequencies, and some dimensionless numbers). In data analysis, the beginning and end of each test item is marked by hand; otherwise, analysis is automatic.

We compared 140 knee patients with 32 healthy controls and found 541 of the 29 x 30 =870 test item movement feature combinations differed significantly between the two groups. From these 541 combinations the DynaPort knee score is calculated by the weighted averages of movement features per item, then weighted averages of items per cluster (locomotion, rising and descending, transfers, lifting and moving objects), and finally the average of the clusters. In an initial study the test-retest reliability of the knee test proved high, and the test turned out to be sufficiently responsive (0.7 patients’ standard deviations improvement after 24 months). However, it remains difficult to interpret the scores in more meaningful terms than merely “better” or “worse”. Extensive reliability studies in the future will further assess the validity of the test and provide more insight into the meaning of the scores.

The DynaPort knee test may thus become an important instrument for evaluating patients’ functional abilities in knee-related clinical practice and research.

The problem of early mechanical stability and late biological osseointegration of the tibial component is still a debated issue in total knee arthroplasty. We are among those authors that stress the necessity of cementing the tibial component to avoid the risk of failure due to the high torque stresses at this interface. In fact while on the femoral edge a good stability can be achieved even in uncemented implants, the stability of traditional tibial components is harder to obtain even in cemented implants.

To solve this problem it has been proposed to use additional devices such as screws, pegs or keels to better fix the tibial plateau. Tantalum monobloc tibial tray is a new answer to this problem. It consists in a cement-less tibial tray made of porous tantalum with monobloc polyethylene. Chemical, physical and biological properties of the raw tantalum are very similar to those of titanium. Porosity of the processed material is 80% (2–3 times compared to plasma spray, beads and fiber mesh coatings) and pores, which diameter is 650 mm, are fully interconnected in the whole bulk of the implant. This trabecular spongy structure, that is not a coating, allows the bone at the interface to deeply grow into the pores, and to achieve optimal stability. In addiction, the fusion of polyethylene into the tantalum mesh completely abolish the back side wear problem. With this technology is yet in use an acetabular component, with which we have a 5 years experience in 150 implants, and now is available a new tibial plateau; the first implant in Europe was performed in our department.

Despite our short series and follow up (6 implants in 2 months) the properties of porous tantalum, already tested in acetabular implants, represent an alternative to the traditional ways of tibial tray fixation.

Tibiofemoral motions are fundamental to the function (strength, stability, ROM) and longevity of total knee replacements (TKR). Although a wide range of TKR kinematics have been reported, few studies have reported kinematics of a single TKR design utilising a variety of tibial articular surfaces. We hypothesised that increased articular constraint, from four different tibial inserts, would result in reduced tibio-femoral translations during dynamic activities.

We tested 22 knees with excellent early clinical outcomes after primary TKR. All knees received the same PCL retaining arthroplasty; with six curved tibial inserts, six flat inserts, six laterally pivoting inserts and four translating/rotating mobile bearing inserts. Fluoroscopic images of knees were acquired during gait, stair, and deep flexion activities. CAD model based shape matching was performed to determine 3D knee kinematics.

There were significant differences in medial condy-lar translations for all activities, none for the lateral condyle. The medial condyle in knees with flat and mobile bearing inserts translated more anterior with flexion than knees with curved or pivoting inserts. Medial condyle translations were greater in mobile bearing knees than knees with flat inserts.

Our results indicate that condylar motions in TKR’s during dynamic activities can be modulated in a reasonably predictable manner by varying the degree of tibio-femoral constraint. Furthermore, the results show that significant control of translation can be achieved through asymmetric tibial insert conformity. These findings suggest it is possible to achieve a particular pattern of tibio-femoral translations and rotations in vivo through careful selection or design of the articular geometry.

Improving the wear resistance of polyethylene is considered paramount to improving knee implant longevity. Consequently, a range of polymer fabrication techniques have evolved in the quest for a highly wear resistant material. The objective of this study was to explore the wear performance of polyethylene as fabricated in a variety of ways.

The following materials were prepared, sterilised, artificially aged, and machined into wear specimens (n = 4 for each material): Compression molded GUR1050 with three levels of cross-linking (120 kGy, 65 kGy, and 0 kGy irradiation – control); ram extruded GUR4150 high modulus material; compression molded GUR4150 low modulus material; and HSS/PolySolidur/Hoechst reference polyethylene. Using a custom designed joint articular wear simulator, samples were loaded for 2 million cycles at a frequency of 0.5 Hz under loads of 2.1 kN. Tests were stopped every 250 000 cycles; and wear surfaces were examined microscopically for surface damage (pitting, cracking, delamination).

After 2 million loading cycles the following specimens were pitted and delaminated: 2 GUR1050 control samples, 3 GUR4150 high modulus specimens, and all 4 reference polyethylene specimens. Burnishing, but no pitting, was seen in all GUR1050 elevated cross-linked polyethylene specimens, and in all GUR4150 low modulus specimens.

The materials tested in this study represent a broad range of fabrication techniques. Differences in starting resin cannot fully account for the differences in wear behaviour seen between the groups; as damage was not limited to one resin group. The cross-linked specimens were melt-annealed, prior to cross-linking. It is possible that this processing step, and not the actual cross-linking, contributed to the improved wear performance of this group. However, of most interest is the comparable wear performance of GUR1050 cross-linked polyethylene and GUR4150 low modulus polyethylene suggesting that cross-linking polyethylene is not the only route towards obtaining a polyethylene with superior wear characteristics.

Range of motion after total knee arthroplasty (TKA) is increasingly an issue of critical concern in the performance of knee replacements and their ability to meet the functional demands of diverse patient populations. The goal of this study was to measure maximum weight bearing flexion in patients with one knee replaced using a posterior cruciate retaining (CR) device and the other a cruciate substituting (PS) device on a prospective basis.

Sixteen patients (32 knees) with bilateral TKA and excellent clinical/functional outcomes at least one year after surgery participated in this study. Eight patients received knee replacements from one surgeon, and eight patients received knee replacements of another design from a second surgeon. Their knees were imaged using fluoroscopy as the patients were asked to bend to maximum flexion with their foot on a 25 cm step. CAD model based shape matching techniques were used to measure knee flexion, axial rotation, and the anterior/ posterior (AP) location of tibio-femoral contact relative to the AP centre of the tibial insert. Paired t-tests were used to evaluate differences in means (p = 0.05).

PS knees had larger average flexion angles (121±8 deg vs. 114±5 deg, p=0.01) and greater femoral rollback (14±3 mm vs. 12±3 mm, p=0.02) than the CR knees. There was no difference in axial rotation (6±4 deg vs. 5±6 deg). The same trends were observed within the single design subgroups.

In patients with heterogeneous bilateral TKA, greater femoral rollback and weight-bearing flexion is exhibited by the knee with a posterior stabilised TKA.

Hip revision failures are partly due to the poor quality of femoral bone stock. Several work showed that bone reconstruction without grafts is possible around a non cemented, stable stem. It is enhanced by a transfemoral approach.

We designed the Restoration TM DLS stem (anatomical, S curved, HA coating and distal locking to ensure a primary stability).

Preoperative planning is necessary. The operative technique is based on a double postero-lateral femoral flaps approach. An innovating and modular instrumentation was developed. It rests on a femoral clamp that solidarises the femur and the trial stem, and allows a precise adjustment of the length and the stem anteversion. A targeting device allows a precise distal locking of the final implant. Osteosynthesis of the flaps is carried out by cerclages in order to bring the bone around the prosthesis.

Forty-seven revisions cases were followed up. No major peroperative incident has occurred. We report one case of locking error. Compared to the planning, the instrumentation was considered to be precise in 94% for the adjustment of the leg length and of the ante-version. The bone adaptation around the implant was generally correct. In 21 cases, it was necessary to carry out metaphysal re-calibration or osteotomies for correction of a femoral deviation. The synthesis of the flaps is stable in 92%. For follow up greater than 3 months, the consolidation of the osteotomies is effective in 90%.

This study made it possible to validate a surgical procedure by transfemoral approach that makes safe implant and cement removal. It also allowed us to validate an innovating, precise yet flexible instrumentation that allows, after preoperative planning, the anatomical reconstruction of the femur around the stem. A perfect proximal adaptation of the femur to the implant is necessary to the good tolerance of the distal locking.

Observations of knee arthroplasty kinematics generally show differences in anteroposterior translation when comparing posterior cruciate retaining (CR) and posterior stabilised (PS) designs. However, the PS cam/post mechanism is not engaged in extension. We hypothe-sised that there would be little difference between CR and PS knee kinematics during stance in gait.

Videofluoroscopy and shape matching techniques were used to quantify motions of 47 fixed-bearing knee arthroplasties (24 CR, 23 PS) during gait and stair-climbing in consenting patients with excellent clinical/ functional performance at least one year post-surgery. The average centre of rotation (COR) was computed for each knee during the two activities; a lateral COR (−50% to 0%) indicates anterior femoral translation with flexion, a medial COR (0% to +50%) indicates posterior femoral translation with flexion.

There was a significant difference between the average COR in the PS (+9%) and CR (−15%) knees for the stair climbing activity (p< 0.001), but not the stance phase of gait (−5% vs. −14%, respectively, p=0.664). The COR was more lateral for the stance phase of gait than for stair climbing in the PS knees (p=0.008), but not the CR knees (p=0.948). All knees showed more axial rotation during the stair activity (8°) than the stance phase of gait (5°, p< 0.001).

During stance in gait, there were small but not significant differences in the centre of rotation between the CR and PS knees. For stair climbing, there were significant differences between CR and PS knee kinematics. These observations are consistent with the hypothesis that CR and PS kinematics ought to be similar near extension, where the articular constraints are similar, but might differ in deeper flexion activities where the intrinsic constraints of the arthroplasty are different. An improved understanding of arthroplasty function should facilitate further evolution of design, surgical techniques, and numerical analyses to optimise patient performance.

Many recent studies emphasise the importance of surgical technique for achieving long-lasting, pain-free, optimally functioning TKR. However, little information exists in the accuracy with which each step of the TKR procedure is performed using current instrumentation. This study examines the accuracy with which each step of the TKR procedure using current, intramedullary instrumentation.

Twenty primary TKR were performed using a current, intramedullary instrumentation system. The accuracy of each femoral and tibial cut and the accuracy of the final frontal and sagittal limb alignment were measured using an image-free computer assisted navigation system. The system made it possible to measure: 1) frontal femoral implant alignment; 2) sagittal femoral implant alignment; 3) femoral implant rotational alignment; 4) frontal tibial implant alignment; 5) sagittal tibial implant alignment; 6) frontal limb alignment; 7) sagittal limb alignment. Alignment results are expressed in terms of the mechanical axis. Optional results are a frontal and sagittal axis of 90° relative to the mechanical axis. The optimal femoral rotational alignment is 3 degrees externally rotated from the posterior femoral condyles or zero degrees externally rotated from Whitesides line.

The alignment results were: 1) frontal femoral alignment: 89° (range 87 to 92°); 2) sagittal femoral alignment: 89 (range 88 to 193°); 3) femoral rotational alignment: 1° external rotation vs. femoral condyle; 2 degrees internally rotated vs. Whitesides line (range 0.5° to 3.5°); 4) frontal tibial alignment: 88° (87° to 93°); 5) sagittal tibial axis: 87° (range 86° to 91°); 6) frontal limb alignment: 179° (range 177 to 181°); 7) sagittal limb alignment 179° (range 174 to 180°).

Intramedullary instrumentation allows reasonably accurate and reproducible frontal limb alignment. There is a tendency to leave the limb in slight flexion when using intramedullary instruments. There is also a consistent tendency to internally rotate the femur with current anterior –posterior alignment guides and to excessively posteriorly flex the tibial component, although almost all of the 20 TKR’s resulted in final limb alignment within 3 degrees of frontal and sagittal axes. Very few (4) TKR’s were performed in which all of the measured steps were within 3 degrees of the optimal position.

The study emphasises that current intramedullary instrumentation does not result in a high incidence of accuracy when each step of the procedure is measured. Computer assisted techniques permit measurement of the steps of the TKR procedure with a high degree (error < 1°) of accuracy. Longevity, pain-relief and funtion should be related to the total accuracy with which TKR are performed.

The aim of the study was to measure in-vivo the 10-year linear and volumetric polyethylene wear of a fully congruent mobile bearing unicompartmental knee arthroplasty (OUKA).

We studied six OUKA’s that had all been implanted 10 years previously. Each patient was examined in even double leg stance at a range of knee flexion angles, in a calibration cage. A stereo pair of X-ray films was acquired for each patient at 0°, 15° and 30° of flexion. The films were analysed using an RSA style calibration and a CAD model silhouette-fitting technique. The position and orientation of each femoral and tibial component was found relative to each other and the bearing position inferred. Penetration of the femoral component into the original volume of the bearing was our estimate of linear wear. The volumetric wear is calculated from the measured linear wear and the known surface area of the bearing. In addition eight control patients were examined less than 3 weeks post-operation where no wear would be expected.and 30We studied seven OUKA’s that had all been implanted at least 10 years previously. A stereo pair of X-ray films was acquired for each patient at 0 Results: The control group showed no measured wear. The seven OUKA’s had an average maximum depth of linear penetration of 0.40 mm at a mean follow-up of 10.9 years. The linear wear rate was 0.033 mm/year. The volumetric material loss was 79.8 mm3. If a steady gradual material loss is assumed, 8 mm3 of UHMWPE was lost per year.

Polyethylene particulate wear debris continues to be implicated in the aetiology of component loosening and implant failure knee following arthroplasty. The OUKA employs a spherical femoral component and a fully congruous meniscal bearing to increase contact area and theoretically reduce the potential for polyethylene wear. The results from this in-vivo study confirm that the device has low 10-year linear and volumetric wear in clinical practice. This may protect the device from component loosening in the long term.

We would like to present an overview of a research programme that aims to improve drastically the state-of-the-art in shoulder joint replacement surgery. Development of Improved endoProstheses for the upper EXtremities (DIPEX), as this effort is called, is a clinically driven multi-disciplinary programme consisting of many contributory projects. Within the project two main directions of research can be distinguished: the development of an improved shoulder prosthesis and the improvement of the surgical process. For this audience, we would like to present our approach to the improvement of the surgical process.

A newly designed visualisation platform called DSCAS (Delft Shoulder Computer Assisted Surgery) will play a central role within the DIPEX project. This platform is not only able to visualise CT and MRI datasets with a range of different algorithms, but is also able to calculate parameters that are essential for surgery and extract information from these datasets. The extracted information serves as input for the Delft Shoulder Model, an inverse dynamic musculo-skeletal finite element model, with which the effect of surgical decisions on the functional outcome, i.e. range of motion, stability of the joint etc. can be predicted and visualised.

Concerning per-operative guidance two approaches are currently studied – a camera-based approach and mechanical approach – that have both their advantages and disadvantages. Comparison of the two approaches in an experimental setting as well as in a clinical setting is part of the DIPEX project.

The ultimate goal of this part of the DIPEX project is to create a surgical support infrastructure that can be used to predict the optimal surgical protocol and can assist with the selection of the most suitable endoprosthesis for a particular patient. Subsequently, this support infrastructure must assist the surgeon during the operation in executing his surgical plan.

Lubricated metal-on-metal (MOM) bearing surfaces are not easily separated, unlike ceramic- or metal-on-UHMWPE (COP, MOP), due to interfacial forces and low diametric clearance that provides a ‘suction-fit’. In vivo videofluoroscopic studies have shown that patients with MOP/COP THRs exhibit separation of bearing surfaces by up to 3.1 mm during normal gait and 5.4 mm during active abduction while patients with MOM bearings do not. In this regard, MOM bearings may have similarities to constrained bearings with the potential to lower dislocation rates.

All patients under 70 years old undergoing primary THRs for primary osteoarthritis were prospectively registered on a computer database. From 1993–8, patients were offered a 28 mm COP bearing. After 1998, as part of a clinical trial, a 28 mm MOM bearing was inserted instead. For all cases, we used a metal-backed, uncemented acetabulum allowing a modular 10-degrees posteriorly augmented insert (Duraloc/PFC/Ultima, J& J) and the same cemented femoral stem (Ultima, J& J). The same experienced surgeon performed all operations using the posterior approach. Interfacial forces between bearing surfaces were assessed in vitro with a variable-speed-motor winch (APT) and a load-cell (E375/RDP) by recording peak-retaining-forces of bearing couples during separation with variable impact-distraction velocities. Statistical analysis used the Chi-square and student’s t-test.

We identified 140 COP THRs in 129 patients and 109 MOM THRs in 100 patients. Nine of 140 (6.4%) COP bearings dislocated within 3 months of surgery compared to 1 of 109 (0.9%) in the MOM group (p=0.024). No significant differences were identified between groups when comparing patient and prosthesis factors. In vitro assessment demonstrated that MOM bearing possessed interfacial retaining forces up to 30N more than COP bearing (p< 0.001).

This study demonstrates a significantly lower dislocation rate in THR with MOM bearing compared with COP. A potential explanation is the differential ease of separation that the two lubricated bearing couples possess due to interfacial retaining forces (viscous tension and ionic adhesive forces) exerted by the lubricating fluid.

Many total knee replacements (TKR) are designed with more conforming articular geometry to increase the femoral contact area and decrease surface stresses. These designs are supported by studies suggesting that implants with coronally flat articular surfaces are vulnerable to medial-lateral lift-off and edge-loading on the polyethylene insert. However, few retrieved inserts from contemporary TKR’s have shown wear consistent with this loading mechanism. This study presents wear measurements from 37 consecutively retrieved polyethylene inserts of the same PCL-retaining design with coronally flat-on-flat articulations. If substantial edge-loading occurred in-vivo, it was hypothesise that wear would be located closer to the medial or lateral edge of the articular surface with a high incidence of delamination.

Inserts were retrieved at autopsy (n=12) after 41 (15–74) months in-situ and at revision TKR (n=25) after 26 (1–71) months in-situ. Reason for revision was infection (28%), patellar component complications (24%), loosening (24%), patellar resurfacing (20%), and supra-condylar fracture (4%). Articular damage was measured using light microscopy and digitising the circumference of each damage region on calibrated images. Surface deformation was measured relative to unused control inserts using a hand-held digitising stylus.

Wear patterns were not significantly different between autopsy or revision retrievals (ANOVA, p> 0.05). Articular wear covered 48%+16% and 47%+14% of the medial and lateral surfaces, respectively. The most frequent wear modes were burnishing and scratching. Delamination occurred on 4(11%) inserts, but involved < 2% of the articular surface. Wear patterns were internally rotated and centrally located. Not one insert had a wear area centroid located in the medial or lateral third of the articular surface. Surface deformations were greatest in the inserts’ central region and the linear deformation rate decreased with time.

Concerns of high contact stresses associated with edge-loading were unsupported by these retrievals. Condylar lift-off, if it occurs, does not appear to substantially impact polyethylene damage in coronally flat-on-flat articulations.

In vitro loading of the proximal femur has improved our understanding of stress shielding after total hip arthroplasty. However, previous load simulators often use simplified loading regimens that may not produce physiologic baseline strains. The purpose of this study was to compare the femoral strain levels produced when using simplified and more complex loading.

A mechanical load simulator was developed which could simultaneously apply a spinal load and nine of eleven available muscle loads to the proximal femur in heelstrike and stair climbing modes. Computer controlled electromechanical actuators were attached to a strain gauged fresh cadaver femur (donor body weight 39 6kg) with metal cables. A spinal load of 668 N (SPL) was applied alone and in combination with individual muscle loads of 267 N to determine the effect of each muscle on femoral strain. The magnitude and direction of the joint reaction force (JRF) was monitored in real time by a three-dimensional force transducer proximal to a metal acetabulum. Anterior, middle and posterior portions of the gluteus medius (ABD), iliotibial band (ITB), short external rotators (SER), vastus lateralis, adductors, rectus femoris, hamstrings, iliopsoas, and gluteus maximus were simulated.

SPL was applied and ABD and ITB were adjusted to produce a JRF magnitude of 2.0 BW. SPL was applied with two combinations of nine muscle loads adjusted in heelstrike mode to produce a JRF magnitude of 2.0 and 2.5 BW and JRF trajectory aligned within one degree of the radiographically determined compression trabecular stream axis.

Both nine-muscle combinations produced lower medial compression strains and substantially lower lateral tension strains than SPL+ABD+ITB in heelstrike and stair climbing. Simplified loading caused a bending moment in the proximal femur resulting in higher strains. Combined loading at 2.5 BW produced compression at 10 of 12 gauges in heelstrike mode and 9 of 12 gauges in stairclimbing.

Total knee replacement (TKR) is intended to satisfy patients rather than surgeons. The latter could be more optimistic when they assess the outcome of their own operations. We envisage that there is a variation between patients’ own assessment and those of surgeons. This study reviewed long-term results of TKR and compared between patients’ assessment and surgeon’s assessment.

Four hundred and six TKR were performed between 1980 and 1994 in a DGH by one surgeon using single knee prosthesis. The follow up was up to 14 years (mean 7.2). Clinical assessment was done by the surgeon in out patient clinic and was compared to the patients’ assessment, which was done through a confidential postal questionnaire (PQ).

Response rate to PQ was 84 %. There was an obvious discrepancy in reporting pain and patients’ satisfaction between the two methods of assessment however there was similarity in other parameters. Surgeon rated satisfaction more highly and patients reported more pain in PQ. In this study revision rate was 4 %, infection 1.7 %, instability 1.4 % and patellar pain 20 %.

There is a variation between patients’ own assessment and those of surgeons. For accurate assessment of the outcome of TKR we recommend the use of postal questionnaire alongside clinical assessment.

Surgical navigation, coupled with preoperative plans, allows surgeons to plan and execute procedures to improve the likelihood of positive outcomes. In real life these navigation systems, which track both the patient and the surgical tools, are not absolutely accurate. Therefore, there is a need to know how much error there may be in the navigation system, so that the surgeon can assess the effects of possible errors in positioning.

The methodology for assessing the accuracy of a surgical navigation system is similar across surgical specialties. We developed a framework for assessing the accuracy of the HipNav system, a computer assisted surgical system used for planning and intra-operative surgical navigation for total hip arthroplasty. This framework can be adapted to other systems and surgical procedures. To assess navigational accuracy, we compared acquired values to a ground-truth model: rigid plastic Sawbones pelvii with mounted fiducials and acetabular implants, whose positions were measured with a coordinate measuring machine. We then identified the individual components of the system that can contribute to overall accuracy, and characterised their contributions to the accuracy of the system. We also measured the end-to-end accuracy of the HipNav system, from initial CT scan through to acetabular cup orientation. This value is of direct importance to the practicing surgeon, and indicates how far off the final measured orientation of the cup may be from its actual location. For the HipNav system, we found that the end-to-end square root of the mean square error was 0.82° in abduction and 0.76° in version.

The accuracy of a surgical navigation system is of vital importance to insure that a preoperative plan is executed properly. To measure the accuracy of a navigation system, accurate models that reflect the relevant anatomy are necessary, and allow true measurement of end-to-end and component accuracy. This example shows how the accuracy of HipNav was assessed, and that the final orientation of the acetabular implant was accurately guided.

Osteolysis secondary to polyethylene wear is the most serious aseptic long-term complication following THR. Studies have shown that fixation with screws, modularity and lack of extensive bone ingrowth are associated with increased osteolysis. This study examines the initial experience with a cup designed to address these issues.

One hundred and twenty-seven consecutive primary THR were performed between 1997–1999 using unce-mented monoblock, elliptical, tantalum cup without screw holes. Average follow-up 40 months (range 24 to 61). 79 THR in females, 48 in males. 48% THR hybrid fixed, 52% uncemented. Average age 61.6 years (range 19 to 88). Pre and post-operative clinical assessment with Harris hip score (hhs), WOMAC, SF-36. One independent, blinded observer performed zonal radiographic analysis with modified DeLee and Charnley method.

Average hhs at recent follow-up 93 (range 85 to 100). All shells appear fixed with bone ingrowth. Dome-gaps present in 6 cups post-op; all have filled in. Radiolucencies at follow-up: 4% zone 1, 8% zone 2; none greater than 1 mm. No cup migration. 8 cup related complications: 5 dislocations (4%) 1 subluxation, 2 undisplaced rim fractures (1.7% – no treatment). 3 dislocations, 1 subluxation occurred more than three months post-op. 3 revisions: 1 deep wound infection, 1 liner exchange (using reaming technique), 1 femoral head exchange.

Uncemented monoblock, elliptical tantalum cup without holes provides secure, symptom-free fixation at 4 years. No complications associated with use of tantalum. Elliptical shape associated with dome gaps, all of which appeared to fill by 3 months. Monoblock design results in increased polyethylene lip prominence associated with 6 cases of instability. Effect of prominent rim on impingement and long-term wear requires careful follow-up.

Pelvic osteolysis secondary to polyethylene wear is a major complication following THR. Identification of implant specific characteristics associated with osteolysis is essential. The purpose of this study is to compare incidence of CT scan identifiable osteolysis in 2 groups of young, active patients following THR; one with multi-holed acetabular shells with screws, one with cups without screw holes.

Between 1990–1993, 77 patients (85 hips) underwent THR with a cementless titanium, multi-holed shell with screws, modular, compression molded polyethylene and an uncemented titanium femoral stem. Average follow-up: 9 years, average age at surgery: 51 years. Between 1984–1987, 163 patients (183 hips) underwent THR with a cementless cobalt-chrome, solid shell, modular, heat-pressed polyeth-ylene liner and uncemented cobalt-chrome femoral stem. Average follow-up: 16 years, average age at operation: 52 years. All polyethylene was irradiated in air. At most recent follow-up, CT scans with metal suppression software was obtained to evaluate incidence of pelvic osteolysis. Patients classified: Group 1-no osteolysis, Group 2-cavitary osteolysis, Group 3-segmental osteolysis.

Patients with titanium, multi-holed shells had: Group 1-50.0%, Group 2-38.7%, and Group 3-11.3%. Patients with cobalt-chrome, solid shells had: Group 1-59.3%, Group 2-33.3% and Group 3-7.4%.

Although the patients with solid cups had much longer follow-up, less secure capture mechanism, less congruency between polyethylene and shell, and heat-pressed polyethylene, the incidence and extent of pelvic osteolysis was less than in the patients with multi-holed shell with screws. The presence of 6.5 mm cancellous screws is a serious independent risk factor for pelvic osteolysis following THR.

In PCL-retaining TKA, tension in the PCL is sensitive to changes in the posterior slope of the tibia component. However, it is not understood how PCL tension, in combination with the absence of the ACL, affects knee kinematics. This study demonstrates the effects of varying posterior tibial slope on the tibiofemoral and patello-femoral kinematics after PCL-retaining TKA.

Eight fresh-frozen lower limb specimens were mounted in a kinematic knee simulator. External forces were applied to create a deep knee bend from 0–110 degrees of flexion, while the three-dimensional motions of the femur, patella and tibia were tracked in real time using a motion analysis system. A PCL-retaining TKA was implanted into each cadaver with the tibial component matching the natural posterior slope of the tibia. After testing, the tibial slope was reduced by four degrees compared to the natural slope, then increased by four degrees compared to the natural slope. With each change in slope, the kinematics of the knee were recorded.

A dramatic change in femoral rollback was observed with increasing slope of the tibial component. In full extension, matching the natural tibial slope displaced the femur 5.7 ± 1.5 mm posteriorly, while more anterior slope and more posterior slope displaced the femur 5.1 ± 2.6 mm and 8.7 ± 2.0 mm posteriorly, respectively. Paradoxically, increased posterior slope resulted in less rollback of the femur during flexion. At 100° a of flexion, total rollback was 11.8 ± 2.6 mm in the intact knee, 6.9 ± 2.4 mm with the natural slope, 9.0 ± 2.8 mm with the anterior slope, and 5.7 ± 2.3 mm with the posterior slope.

Preserving the PCL allows the femur to rollback on the tibial plateau with knee flexion. However, increasing the natural slope of the tibia causes a significant posterior shift of the femur in extension thus reducing rollback in flexion.

Proximal femoral bone loss is often observed after total hip arthroplasty (THA) and continues to complicate revisions. The purpose of this study was to evaluate the clinical and radiographic outcomes of patients with the unusual finding of proximal femoral cortical hypertrophy after THA or endoprosthesis.

Three patients were identified with femoral stem tip perforation through the posterolateral femoral shaft cortex. Known risk factors for perforation were osteoporosis, distal osteolysis causing late stem migration, and endoprosthesis after previous fracture/internal fixation. Two patients had dual energy x-ray absorptiometry (DXA) of both hips. Follow-up was 16, 17 and 28 years.

All three patients had clinically stable femoral components and none had thigh loading pain. All three patients had dense cortical bone buttressing the undersuface of the implant collar and a dense medial femoral cortex. Proximal femoral DXA regions of interest were 120 and 145% of the contralateral femur in the migration and post-fracture endoprosthesis patients, respectively.

The endoprosthesis patient was revised to a THA 28 years post-operatively due to acetabular erosion. Excess dense cortical bone in the proximal femur was removed with a high speed bur and enabled revision with a primary non-cemented femoral component.

Common factors which appeared to be necessary for a stable implant with proximal femoral densification included collared femoral components, stem alignment more vertical than the femoral neck axis, stem perforating the posterolateral femoral cortex, no inhibition of translation along the stem axis by cement or biological ingrowth, and not having the implant revised despite its unorthodox appearance.

Long-term maintenance of the proximal femoral cortex after THA or endoprosthesis is possible. Paradoxically, a rare subset of the complication of femoral shaft perforation demonstrated by these anomalous cases suggested an alternative approach to the prevention of stress shielding bone loss after THA.

Radiolucencies are generally thought to be a manifestation of loosening. They are commonly seen under the tibial component of the Oxford Unicompartmental knee replacement. However, they are not associated with long term failure [1]. The aim of this study was to investigate any relationship between radiolucencies and component migration.

Eight medial Oxford Unicompartmental knee prostheses were examined post-operatively, at 12 months and at 24 months using Roentgen Stereophotogrammetric Analysis (RSA). The serial radiographs were calibrated and three dimensional CAD models were matched to the extracted component shapes. Implanted bone marker balls were then selected on all radiographs. The components were superimposed. Migration calculation was achieved by comparing relative positions of components to bone marker balls in the serial radiographs. Fluoroscopically screened X-rays were taken to determine whether there were any radiolu-cencies under the tibial component.

By 12 months, the femoral component had migrated significantly anteriorly (0.35 mm) and proximally (0.61 mm). The tibial component had migrated significantly distally (0.42 mm) and anteriorly (0.47 mm). Although on average there appeared to be a small further migration between 12 and 24 months, this was not statistically significant in any direction.

Six of the eight patients had radiolucencies at 24 months. None of the radiolucencies were was complete. The maximum radiolucency was 1 mm thick and the average was 0.57 mm. There was no correlation between radiolucency and migration.

The proximal femoral migration and distal tibial migration can be explained by the load across the knee. We cannot yet explain the anterior tibial migration. Radiolucencies almost always occur and are not related to migration.This confirms they are not associated with loosening.

The disadvantages of sawing for precise bone cuts are well known: untrue cuts, heat and metal wear. The main limiting factors of available milling devices are the difficult handling and high costs, especially if the devices are based on a robot. Supported by clinical users and mechanical engineers a milling concept adopted from machining has been realised in order to overcome this limitations. The „All-in-One Milling-Tool“ achieves the same precision of a robot by a mechanically guided milling resection far below the necessary investment for a robot. Three methods are provided for the alignment of the resection planes and will be discussed: intramedullary adjustment, 3D CT-based planning and intramedullar performance as well as the performance under control by navigation. All versions are based on a handheld resection and guarantee a visual and haptical feedback for the surgeon. The use of navigation has the advantage of the accurate transfer of the 3D plan into the OR, the interactive facilitated alignment und resection steps and the documentation of planned and actual implant position.

When the Oxford unicompartmental meniscal bearing arthroplasty (UCA) is used in the lateral compartment of the knee 10% of the bearings dislocate. An in-vitro cadaveric study was performed to investigate if the anatomy and joint geometry of the lateral compartment was a contributory factor in bearing dislocation. More specifically, the study investigated if the soft tissue tension of the lateral compartment, as determined by the length of the lateral collateral ligament (LCL), was related to bearing dislocation. A change in length of greater than 2 mm is sufficient to allow the bearing to dislocate.

The Vicon Motion Analysis System (Oxford Metrics, Oxford, UK) was used to assess length changes in the LCL of seven cadaveric knees. Measurements were made of the LCL length through knee flexion and of the change in LCL length when a varus force was applied at a fixed flexion angle. Measurements were made in the normal knee and with the knee implanted with the Oxford prosthesis.

In the intact knee the mean LCL change was 5.5mm (8%) over the flexion range. After implantation with the Oxford UCA the mean change in length was only 1 mm (1%). There was a significant difference in the LCL length at 90° (p=0.03) and 135° (p=0.01) of knee flexion compared to the intact knee. When a varus force was applied the LCL length change of the intact knee (5.4 mm) was significantly different (p=0.02) to that of the knee with the prosthesis implanted (2.7 mm)

This study used a new method to dynamically measure LCL length. It found that after implantation of the Oxford lateral UCA the LCL remains isometric over the flexion range and does not slacken in flexion as it in the normal knee. This would suggest that the soft tissue tension was adequate to contain the bearing within the joint.

However, when a varus force was applied the LCL did not sufficiently resist a displacing force producing an LCL length change greater than 2 mm.

The evidence provided by this study is contradictory. The “lack of change in LCL length through flexion” suggests that the ligament remains tight through range and is unlikely to allow dislocation. However, the amount of distraction possible when an adducting moment is applied is sufficient to allow bearing dislocation. The length tension properties of the lateral structures are therefore implicated in the mechanism of dislocation.

To determine the effect of altering tibial slope on the two-year range of motion (ROM) of patients undergoing condylar total knee replacements (TKR).

A single surgeon performed 74 primary cemented posterior stabilised tri-compartmental TKR’s on 56 patients (19 male, 37 female) with mean age of 67.1 years, height 66.7in., weight 187.4 lb, and BMI 29.58 kg/m2. 51 had osteoarthritis, and five had rheumatoid arthritis. A standard surgical technique was employed utilising flexion axis localisation to position the femoral components. Patients were followed for two years minimum using outcome measures and x-rays. Knees where tibial slope was restored to a degree angle equal to, or slightly greater than, their pre-op slope (group 1) were compared to knees where tibial slope was decreased (group 2).

The average 2 year post-op ROM in Group 1 was significantly greater than that of Group 2 (129.3 degrees vs. 120.5 degrees, p=.001). The average pre-op to post-op increase in ROM in Group 1 was significantly greater than Group 2 (38.1 degrees vs.27.7 degrees, p=.003). Correlational analysis revealed that restoration of pre-op tibial slope was the primary determinant of post-op ROM, followed by pre-op ROM, then weight and BMI (each to significance of p< 0.05).

Restoration of tibial slope clearly produced increased ROM in this study. Using one standard slope cut for every tibia may prevent many patients from achieving their maximum potential ROM.

The aim of the study was to compare clinical results after cruciate-retaining total knee arthroplasty (TKA) between the ceramic and the Co-Cr alloy condylar prostheses.

In a prospective semi-randomised study, 218 patients underwent cruciate-retaining TKA with the Co-Cr alloy prosthesis (Kinemax®, Howmedica) or the LFA-I® prosthesis (Kyocera) composed of an alumina ceramic femoral component and a titaniumalloy tibial component with a UHMWPE insert. In each surgery, both components were fixed with PMMA cement. All the patients underwent the same postoperative management. Finally, 110 knees with the ceramic prosthesis and 84 knees with the Co-Cr prosthesis were followed up for 24 to 124 months (the average of 56 months).

Two revisions were performed in each group (tibial tray breakage and infection in the ceramic group, and loosening and infection in the Co-Cr group). In the remaining patients, there were no significant differences in the HSS knee score (85 and 86 points, respectively) and the ROM (112 and 113 degrees) between the two groups. In radiological evaluation, a radiolucent line was more frequently observed with the significance (p< 0.05) in the Co-Cr alloy group (9.5 %) than in the ceramic group (2.7 %).

In the mid-term follow-up evaluations, the clinical results of the ceramic TKA are equivalent to those of the Co-Cr alloy TKA. In addition, the ceramic prosthesis showed some statistical tendency of superiority to the Co-Cr prosthesis concerning the radiolucent line. These results encouraged us to conduct a long-term follow-up study on the ceramic total knee prosthesis.

The Acrobot®, an active constraint “hands-on” robotic system, gives navigation cues to the surgeon, and also assists him in the surgery, using active software constraints if he tries to depart from the preoperative plan. It has just entered clinical trials. We report the first 5 cases.

The Acrobot® system for precision total knee arthroplasty comprises the following components:

1. A CT-based planning system

a gross positioning device with separate brakes and encoders, locked off for safety during the procedure,

4. The Acrobot’s software which:

imports the preoperative plan,

Each patient’s knee scores were monitored and postoperative CT scan was compared with the preoperative plan.

Seven robot assisted arthroplasties have been performed. No significant complications have been encountered. The Knee and Womac Scores show that the procedure is safe and comparable to conventional surgery in the early postoperative period. The envelope of error on postoperative CT scans has been within the accuracy of the method of measurement, at < 1 mm and < 10 without the outliers which haunt every clinical series.

The Acrobot® system for total knee arthroplasty has completed its preliminary trial satisfactorily. It provides a handson operation but with robotic levels of accuracy. It is suitable for conventional open surgery, but its real place will be in the arena of minimally invasive unicondylar knee arthroplasty, hip arthroplasty and resurfacing, and in the spine, where active constraint will prevent potentially dangerous surgical errors.

Most of the approaches to computer aided surgery currently in use share the need for an accurate pre-operative surgical planning to establish the optimal conditions that the surgeon should achieve using such specialised instrumentation.

The penetration of these computer-aided planning tools in the clinical practice is still limited. The systems that replicate such 2D planning are user-friendly, but lack the full three-dimensional definition of the implant position. On the contrary, systems based on CT data, which allow a fully 3D planning, usually have cumbersome interfaces. Last but not least all programs currently available are only aimed to visualise the position and orientation of the prosthetic components, presuming that the anatomical referencing is sufficient for the surgeon to decide the correctness of the planning.

The Hip-Op research project was aimed to the development of a complete surgical simulation software environment for the pre-operative planning of total hip replacement surgery. The software had to fulfil the following basic requirements: a CT-based three-dimensional planning environment; a user-friendly graphic user interface based on the Multimodal Display approach; the possibility to integrate analysis modules aimed to provide the surgeon with additional functional data; complete independence from the type of hip prosthesis or from the intra-operative instrumentation.

The graphical interface of Hip-Op is based on an innovative visualisation paradigm, which is called Multimodal display. Hip-Op represents the anatomical objects by means of multiple views, each of which simulates a different medical imaging modality familiar to the medical professional. Two analysis modules are currently integrated in Hip-Op to provide clinically relevant 3D indicators of the implant fit and fill in the host femur.

The relative motion between a prosthesis, the cement mantle and its’ host bone during weight bearing is not well understood. Using Radiostereophotogrammetric Analysis (RSA), we examined the dynamically inducible micromotion that exists at these interfaces when an increased load is placed through the prosthesis.

Dynamically inducible micromotion was measured in the femoral components of 21 subjects undergoing total hip replacement with polished Exeter stems. Two standing RSA studies were performed, at 3 and 12 months postoperatively. Firstly in double-leg stance, and secondly fully weight bearing through the operated hip.

Subjects had no signs of clinical or radiological signs of loosening at 1 year. Significant micromotion was detected at the prosthesis-cement interface at 3 months.

Similar patterns of micromotion were observed at 12 months. The prosthesis appeared to bend during single-leg stance weight bearing, however this accounted for less than half of the total observed movement.

Conventional RSA studies were conducted at 3 months, 6 months and 1 year to confirm that the implants showed normal migration patterns.

This study demonstrates that movement exists between the prosthesis and bone during cyclical weight bearing. This dynamically inducible micromotion probably occurs at the prosthesis-cement interface. It could account for the wear that is observed on the surface of retrieved secure prostheses. This may be a mechanism by which failure eventually occurs.

The Birmingham reSurfacing Arthroplasty (BSA) is a metal on metal prosthesis with no published independent clinical studies. Despite this, it is increasing in popularity, especially as an alternative to stemmed prostheses in younger patients. This study presents the 1year migration results of the BSA femoral component using Roentgen Stereophotogrammteric Analysis (RSA).

Twenty six subjects underwent a BSA, through the postero-lateral approach using CMW3G cement, with RSA marker balls placed intra-operatively. The femoral component migration was measured at intervals of 3, 6 and 12 months using the Oxford RSA system. Geometric algorhythms were used to identify the femoral component. The data was examined for distribution prior to analysis. All statistical analysis was performed using the t-test.

The data was normally distributed. The 1 year migration results of the BSA femoral component are displayed below.

All cemented implants migrate in vivo. The majority of cemented stemmed implant migration occurs within the first post-operative year. High rates of migration within the first post-operative year correlate with premature component failure in some instances. The BSA is a fundamentally different design to most cemented prostheses, despite this we know that very large migrations, those in excess of 2mm/year in any direction are generally regarded as poor indicators of long term outcome. These results suggest that the BSA femoral component is an inherently stable device as it does not migrate significantly within the first post-operative year. Only long-term independent clinical studies and continued RSA follow-up will enable a comprehensive evaluation of the device.

Limitations in the material properties of arthroplasty bearings have been a major impediment to increasing the longevity and durability of total joint replacement. These limitations most often manifest as wear debris related osteolysis and bearing failure. While these problems cause serious complications in THR and TKR, as arthroplasty is applied to the spine, such problems could become catastrophic. An ideal bearing material and design would be biocompatible, provide for restoration of normal range of motion, and be durable enough to sustain long term unrestricted high demand activities without mechanical failure, significant wear, or contribution to particulate related osteolysis. A new material, Polycrystalline Diamond Compact (PDC), appears to closely approximate the ideal bearing material for applications from large joints to intervertebral discs.

PDC is a diamond structure formed at ultra high pressure and temperature and bonded to a metal substrate. Bond strength to substrate approximates substrate tensile strength. PDC has unprecedented impact toughness and hardness, and has the lowest unlubricated coefficient of friction of any manmade contact bearing. A screening study was used to evaluate wear properties with ceramic and CoCr controls. Full prototypes were tested in a PMED hip simulator for 10 million cycles and on a spinal disc simulator for 30 million cycles.

In the screening study, PDC specimens demonstrated a significant advantage in wear over controls, whose wear rates were consistent with earlier studies. In simulator studies, the PDC specimens experienced extremely low wear at 10 million cycles (~1.0 mg per bearing surface) under austere conditions of no lubrication. In the spinal disc simulator, wear was approximately 0.3 mg at 20 million cycles under similar austere condition.

PDC’s unique material properties lend themselves to designs with thin (5 mm) acetabular bearings that provide for improved ROM and decreased dislocation risk, as well as to spinal applications where space is at a premium. Its properties of extraordinary impact toughness and high wear resistance lend themselves to arthroplasty applications which may require no undue activity restrictions, and may make prostheses available in which bearing wear and mechanical failure are no longer a factor affecting longevity.

Purpose: Management of supracondylar fractures of the humerus becomes a controversial issue when there is major displacement. The risk of vessel and nerve injury is very high, making reduction and fixation particularly difficult.

Material and methods: We conducted a retrospective analysis of 100 supracondylar fractures managed over a ten year period. All of these fractures were in extension and exhibited a bone gap. We analysed early and late complications.

Results and discussion: Mean age at trauma was 6.5 years, with six boys for four girls. The left side was involved in 69% of the cases. Falls were the predominant cause (48%).

Thirty-two percent of fractures were complicated initially: nerve injury (n=17), vascular injury (n=12) (including three cases with nerve and vascular injury), open fractures (n=7). The medial nerve was injured in most cases (n=12). Ulnar palsy was noted in four patients and radial palsy in one. Vessel injury led to abolition of the radial pulse in eight patients and the ulnar pulse in one; all resolved after reduction. Ischaemia of the hand was noted in two cases before reduction of the fracture but vascular surgery was not required.

Most of the fixations were achieved with cross pinning (percutaneous insertion in 47 patients and open surgery in 13). Despite minimal medial skin incision, ulnar nerve deficiency was observed after surgery in seven cases; four were rapidly regressive and three required surgical exploration with neurolysis. Six revision procedures were required for secondary displacement (10%).

The 26 Judet fixations led to ten secondary displacements requiring surgical revision for cross pinning. Four cases of postoperative ulnar nerve deficiency were noted: reoperation to release the nerve pinched in the fracture was required for only one patient.

The Blount technique was used in nine cases with four secondary displacements, including one related to two sites of nerve impingement.

Five cases of superficial pin tract infection which resolved rapidly and two cases of deep infection were noted in the early postoperative period.

Formation of a varus ulnar callus was noted in five cases: two required secondary surgery for correction.

Conclusion: Our results point out the high rate of vessel and nerve complications related to these supracondylar fractures of the humerus with displacement. We recommend cross pinning which is mechanically superior and which does not compromise the neurological result if a minimal medial incision is used.

Purpose: A prospective study was conducted in 160 children presenting varus trauma of the ankle. The purpose of the study was to validate the Ottawa ankle rules in children. Application of the Ottawa rules can reduce the number of x-rays by 25% but little work has been reported concerning their validation (Chande 1995).

Material and methods: One hundred sixty children, 71 boys and 89 girls, mean age eleven years three months (range 3 – 15 years) were included in this study conducted between February 2001 and December 2001. Clinical presentations with an obvious diagnosis of ankle fracture were excluded (six patients). Epidemiological and clinical data and the initial Ottawa criteria were recorded on a data sheet with a specific number of assigned items. A standard radiographic work-up with an anteroposterior, lateral and oblique view of the ankle was obtained in all cases. All patients were seen at a second consultation on day 8 by another physician to confirm diagnosis. The x-rays were read three times: by the emergency care physician, and by a second physician and a paediatric orthopaedic surgeon at the 8-day consultation.

Results: Diagnosis which were confirmed were: benign sprains (BS) (n=71), moderately severe sprains (MS) (n=47), severe sprains (SS) (n=2), type I epiphyseal detachment (ED) (n=21), fractures (n=13) (8 fifth metatarsal, 1 triple fracture line, 1 medial malleolus, 2 lateral malleolus, 1 tarsal scaphoid).

For the Ottawa criteria, ankles positive for pain and at least one other criterion were: 64/77 BS, 43/47 MS, 2/2 SS, 21/21 DE and 13/13 fractures. All fractures were diagnosed at the first exam or at the 8-day exam.

Discussion: Based on our findings, the clinical Ottawa rules cannot be considered to be validated for children. Using these rules, x-rays would have been performed in 143 patients to identify 13 fractures that were not clinically obvious. Because the Ottawa rules are insufficiently specific for children, we recommend, like Brooks (1981) to use more rigorous clinical criteria for the diagnosis of ankle trauma in children.

The diagnostic criteria used in this study enabled correct first intention diagnosis in 129 patients with trauma. We propose ordering x-rays only for children with signs of moderate or severe sprain or pain in zone C (base of the fifth metatarsal: 8/8) or E (medial border of the foot: tarsal scaphoid fracture). For other cases (98/160) physical examination is sufficient.

Conclusion: We do not consider the Ottawa clinical rules to be valid for varus ankle trauma in children. We propose clinical criteria which can limit the number of x-ray work-ups by 60% in children with this type of trauma.

Purpose: The purpose of this work was to present the long-term outcome after resection of thoraco-lumbar, lumbar, or lumbosacral hemivertebrae in 69 children.

Material and methods: Sixty-nine children (35 girls and 34 boys) underwent surgery at a mean age of 3 years (range 1 year – 10 years 6 months). Mean follow-up was 6 years (range 6 months – 18 years). Resections involved thoracolumbar (n=20), lumbar (n=34), and lumbosacral (n=15) hemivertebrae. Congenital vertebral and visceral malformations were present in 32% and 41% of the children respectively. Ten patients had an underlying neurological malformation.

A single operation was performed in 60 patients using a combined anterior and posterior approach and convex posterior CD baby instrumentation. Nine patients underwent two operations one week apart. All patients wore a corset brace for six months.

Results: Structure curvature: the mean Cobb angle was 35° preoperatively, 16° postoperatively, and 15° at last follow-up.

Compensating curvature: the mean Cobbe angle was 21° preoperatively and 12° at last follow-up. Complications: partial deficit of the anterior tibialis (n=1), nonunion (n=3), infection (n=1), disassembly (n=3), valgum tibia at the site of the fibular graft harvesting (n=1).

Discussion: At these spinal levels, hemivertebral resection appears to be the most appropriate technique for children aged less than three years as long as there are no clear signs of progressive curvature.

Purpose: Tillaux fractures correspond to type III joint fractures involving the anterolateral tubercle of the inferior tibia in the Salter and Harris classification. These fractures generally occur by external rotation in children about 13 years old at the time the medial part of inferior growth cartilage of the tibial epiphysis has fused. The purpose of the present study was to analyse long-term outcome in a retrospective series of twenty children.

Material and methods: All twenty patients underwent physical examination and a standard radiographic work-up at last follow-up. Results were classed into three categories: good (free of pain, stiffness, gait impairment, joint degeneration), faire (moderate pain and/or stiffness and/or gait impairment without joint degeneration), poor (severe pain and/or severe stiffness and/or limping and/or joint degeneration).

Results: This series included eight boys and twelve girls, mean age 12.8 years (range 3.4 – 14.9). Mean follow-up was three years eleven months (range 12 months – 8 years 9 months). Eleven patients underwent surgical treatment and nine orthopaedic treatment. The lateral segment of the growth cartilage was open in all cases but the medial segment was open in two and completely closed in six. A computed tomography scan was required in one patient to assess displacement. Outcome was considered good in eighteen patients and fair in two. These two patients had persistent pain without functional impairment at about one year follow-up.

Discussion: Overall, the long-term outcome is good for Tillaux fractures if they are correctly identified and evaluated, with computed tomography if necessary, to enable appropriate surgical or orthopaedic treatment. Inappropriate management of this joint fracture can lead to joint incongruency and secondary degeneration. Most of these fractures occur in adolescents and secondary growth impairment is negligible. This type of fracture may also occur in adults. Prognosis is excellent with adapted treatment.

Purpose: Reconstruction after resection of malignant bone tumours remains a major challenge. Free vascularised fibular grafts may be a useful alternative in this indication.

Material: Thirty children (nine girls, twenty-one boys) were treated between 1993 and 2000. Mean age was eleven years. Tumour histology was: osteogenic osteo-sarcoma (n=20), Ewing tumour (n=5), justacortical osteosarcoma (n=3), synovialosarcoma (n=1), and chondrosarcoma (n=1). Tumours were located in the femur (n=17), the tibia (n=6), the humerus (n=5), the radius (n=1), and the distal fibular (n=1). The length of resection varied from 100 mm to 260 mm (mean 160 mm). Internal fixation was used in 27 cases and external fixation in three. The adjacent epiphysis was preserved in 22 cases and initial arthrodesis was performed in eight.

Method: Patients were followed clinically and radiographically. A bone scintigram was obtained in all patients at least once during the postoperative period. Radiological assessment was based on the hypertrophy index of the graft using the method described by DeBoer and Wood. Functional outcome was assessed using the Enneking criteria.

Results: Mean follow-up was 51 months (range 2 – 9 years). Early amputation was required in two patients due to local ocological complications. One patient died at eight months follow-up due to lung metastasis. Among the remaining 27 patients, primary bone healing was achieved in 22. The five other patients exhibited clear signs of non-vascularisation. Successful healing was achieved in four of these patients after a complementary autologous graft. All cases of stress fracture healed after simple immobilisation.

The twenty-two patients who achieved primary bone healing developed a hypertrophic graft (mean 61%, range 22 – 190%). Graft hypertrophy was not observed in the five cases requiring a secondary graft after the scintigram demonstrated lack of vascularisation. Hypertrophy of the vascularised fibular graft was more marked for lower limb reconstructions than for upper limb reconstructions..

Functional outcome was satisfactory in all cases. On the 30-point Enneking scale as modified, our patients achieved a mean 26 points (range 19 – 30).

Discussion: Outcome was directly related to patency of the vascular anastomoses. Bone scintigraphy, performed one month after reconstruction surgery, was an important element for assessing prognosis. In case of unsuccessful vascularisation, a complementary cortico-cancellous graft should be used. Early weight-bearing is advisable using adequate protective devices. Dynamic osteosynthesis systems should be helpful in improving graft hypertrophy.

Purpose: Amputation is often proposed for malignant tumours of the distal tibia. The purpose of our study was to report outcome and complications after conservative treatment of osteosarcoma of the distal tibia.

Material and methods: Eight patients, four boys and four girls aged 8 – 16 years (mean 12 years) were managed conservatively with high-dose methotrexate chemotherapy for osteosarcoma of the distal tibia between 1983 and 1998. Wide resection was performed in all cases and one patient had a lung metastasis. Mean length of resection was 13 cm (9–19). Tibiotalar reconstruction arthrodesis was performed in seven patients. Tibial grafts and a centromedullar nail associated with fibulotalar arthrodesis with screw fixation were used in four patients. Plate fixation was used in two, and one patient had a cement spacer while waiting for biological reconstruction. After surgery, the patients were immobilised in a plaster cast for three to six months. Weight bearing began two to four months after surgery.

Results: Resection was wide in four cases, marginal in three , and contaminated in one. Four patients responded well to chemotherapy and four responded poorly. Outcome was assessed at a mean follow-up of 5.5 years (2–17 years). At last follow-up, six patients were in remission, and two had died, including one after local recurrence despite amputation. Three patients had a deep infection which cured in all three without surgery. Two revisions were required in one patient with nonunion before achieving a solid union. All the patients who had a tibiotalar arthrodesis progressively developed nearly normal “ankle” function subsequent to progressive sub-talar hypermobility. The mean MSTS score was 27.7/30 (range 22 – 30).

Discussion: Conservative management of osteosarcoma of the distal tibia appears to be feasible and provides excellent functional results despite an important risk of infection. Wide surgical margins requires a good response to chemotherapy. In case of doubt, reconstruction must avoid contaminating the rest of the tibia in order to allow secondary amputation if needed.

Purpose: Infection after resection and total knee arthoplasty for malignant bone tumours in children is a serious complication which may compromise limb salvage. The purpose of this work was to study the aetiology, treatment and prognosis of this event.

Material and methods: Among the 169 total knee arthroplasties performed for malignant bone tumours between 1981 and 1999, we selected 17 patients meeting the following criteria: proven infection with identified germ on deep samples or presence of a fistula more than two years after surgery. All of the patients had osteogenic sarcomas (excluding Ewing sarcomas which account for 30% of the tumours in this localisation). The bone tumour involved the femur (n=11) or the tibia (n=6) and required extraarticular (n=14) or transarticular (n=2) resection. Infections were primary (n=9) developing after the first operation, or secondary (n=8) to surgical revision in six, joint wound in one, or haematogeneous dissemination in one patient. The causal germ was identified in thirteen patients (76%) and was a staphylococcus in all cases. Treatment included systemic antibiotics and lavage (n=10), one-procedure change in prosthesis (n=3), removal of the implant with replacement by a spacer (n=2), surgical abstention (n=2), or amputation (n=1).

Results: Mean follow-up was eight years (2 – 16 years). On the average, treatment of infection lasted 51 months and required a 3.9 surgical interventions. At last follow-up, infection was considered cured in 70% of the patients who were free of clinical or laboratory signs of infection without antibiotics for at least one year. The arthroplasty could be preserved in one-third of the cases (22% of the primary infections and 50% of the secondary infections). Another treatment, arthrodesis (n=6), Borggreve procedure (n=1), or amputation (n=4), was given in the other two-thirds.

Discussion: The 10% complication rate observed here is in agreement with data in the literature. Development of primary infection is influenced more by the histology of the tumour and the presence of skin wounds (methotrexate) than by tumour site or type of resection. The diagnosis of primary infection is made late, often at the end of the postoperative chemotherapy protocol. Changing the implant is the ideal treatment. Secondary infection is characteristically less difficult to diagnose; infection is recognised earlier and the chances of preserving the implant are better.

Purpose: Therapeutic options for shaft reconstruction are allografts, shaft prosthesis, and autografts, which may be vascularised or not. The purpose of this work was to assess mid-term results and complications after upper limb reconstructions using a vascularised fibula in children and adolescents undergoing surgery for tumour resection.

Material and methods: A vascularised fibular graft was used for reconstruction in ten patients who underwent surgery for resection of upper limb tumours between 1994 and 2000. The patients were seven boys and three girls, aged seven to seventeen years. the vascularised fibula was used for reconstruction after tumour resection in the same operation for eight patients and to salvage a proximal humeral prosthesis in two patients. The eight single-procedure reconstructions concerned four resections of the humeral shaft and four resections of the radius. Tumour histology was: classical osteosarcoma (n=7), low-grade osteosarcoma (n=1), Ewing tumour (n= 1) and aggressive enchondroma (n=1). Six patients were on chemotherapy at the time of the fibular transfer.

Graft lengths varied from nine to 21 cm (mean 14 cm). Plate fixation was used in most cases. All patients wore a cast for six to twelve weeks after surgery.

Results: Results were analysed retrospectively after 3.9 years follow-up (range 1 – 7 years). Mean time to bone healing was three months (range 1.5 – 5 months). Five of the six humeral shaft reconstructions fractured due to trauma, requiring revision surgery in four cases. All patients who were reoperated achieved bone healing rapidly. One radius had to be revised to add supplementary bone. The mean functional score (MSTS) was 25.5/30 (range 21 – 30). One patient died from lung metastasis and the others exhibited complete tumour remission.

Discussion: Vascularised fibula reconstruction of the upper limb provides good radiological results, particularly for the radius. For the humerus, the results are better for younger children because the bone can grow in thickness. Certain mechanical complications may occur if normal sports activities are resumed too early. Functional outcome after these shaft reconstructions is nearly normal.

Purpose: We performed a biometric evaluation of the femoral trochlea in the human foetus and compared measurements with those observed in the adult in order to search for correlations with other biometric parameters of the human femur.

Material: Twenty-two foetuses with no orthopaedic anomalies were preserved in formol. The 44 knees were studied. Fœtal age varied from 26 to 40 weeks.

Method: After anatomic dissection, digital photographic documents were analysed using angular measurement software. The following dimensions were measured on the distal epiphysis: anteroposterior thickness of the condyles, protrusions of the lateral and medial trochleal edges, the difference in condyle height, the trochlear opening angle alpha, trochlear slope. Femoral anteversion, length of the femoral neck, and the neck-shaft angle were measured on the AP view of the femur.

Spearman’s test was used to search for correlations. Results were compared with those measured under the same conditions in a series of 32 adult knees published by Wanner.

Results: The alpha angle of trochlear opening was 148° with a coefficient of variability of 4%. The alpha angle was greater than 150° in 18 trochleae. The lateral edge of the trochlea was higher than the medial edge in 37/44 trochleae. There was no correlation by age and sex.

The femoral measurements showed 27.01° anteversion with very wide variability (coefficient 46%) and no correlation with trochlear opening.

No significant differences were observed between the fœtal and adult measurements.

Discussion: Our data are the first reporting anatomic measurements of the fœtal trochlea. The morphology of the lower extremity of the femur during the third trimester of pregnancy is globally the same as in adult femurs. Morphological changes of the proximal femur occurring during growth do not appear to modify the morphology of the distal femur. The deep and asymmetrical engagement of the patella onto the trochlea is a characteristic of modern man and is considered to be a consequence of bipedal stance. Our study would appear to confirm that the anatomic characteristics of the human trochlea have been integrated into the genome in the course of evolution. This suggests that a genetic origin of trochlea dysplasia, as suggested by Dejour, is a reasonable hypothesis.

Purpose: We reviewed a series of pollicizations in children with congenital thumb malformations. The purpose of this study was to assess the influence of anatomic or technical factors on functional and cosmetic outcome.

Material: The series included 33 operations in 26 children. The Blauth classification was: grade IIIA (n=1), grade IIIB (n=8), grade IV (n=8), grade V (n=13), mirror hand (n=8). We noted the type of skin incision, technique used to fix the metacarpal head on the carpus, and tendon shortenings. Results were assessed at mean 4 years follow-up on the basis of the cosmetic aspect (parent satisfaction) and functional outcome measured with the Kapandji index and flexion-extension of inter-phalangeal joint, thumb finger opposition, and sensitivity.

Results: Mean age at surgery was 32 months. Fixation was achieved with sutures in 24 cases and pinning in nine. Tendon shortening was performed in 16 cases on the extensor system and in one case on the deep flexor system. Mean follow-up was four years. There was no significant difference between groups A and B for cosmetic outcome. The main factor influencing objective functional outcome was the association of a grade III or IV radial club hand. In these patients, the final outcome was compromised by the stiffness or deformation of the radiocarpal joint and the stiffness of the preoperative Kapandji index which was 7 (mean) in group A and 4.75 in group B.

Discussion and conclusion: The following technical aspects did not have a significant effect on the final functional result in our series: type of skin incision, type of carpal fixation, shortening the extensor or flexor system. Technical aspects which must be performed with particular care include reconstruction of the thenar muscles using interosseous muscles, curettage of the growth cartilage of the head of the second metacarpus, and hyper-extension of the head of the second metacarpus during fixation onto the carpus. Careful technique avoids future complications such as excessive growth of the neometa-carpus or Z-thumb.

Purpose: We searched to define a fracture index useful for predicting the risk of bone fracture in children with essential bone cysts.

Material and method: We reviewed 96 children with an essential bone cyst. The following clinical data were recorded: age, cyst localisation, circumstances of diagnosis.

The radiological analysis was based on 193 AP and lateral x-rays. We measured: 1) the distance separating the superior pole of the cyst from the suprajacent growth cartilage, 2) the largest cyst diameter, 3) the greatest cyst height, 4) the thinnest cortical width facing the cyst, 5) the cyst surface area calculated exactly using surface area software and expressed as a a ratio of shaft diameter (S/d2, Kaelin index). These different parameters were compared for cysts associated with fracture or not.

Results: Mean age at diagnosis was 10.4 years (range 2 – 12.8 years). Most of the cysts were located in the upper portion of the humerus (72%). Fracture was the inaugural sign in 68% of the cases.

Comparing the two cohorts of patients demonstrated that the following differences were significant (Student’s t test): 1) cyst width (p=0.0038): below 16 mm none of the cysts fractured. For wider cysts, there was no difference between the fracture and non-fracture cysts. 2) cortical thickness (p=0.0002); cortical thickness greater than 5 mm protected against fracture. If the cortical measured less than 3 mm, the risk of fracture was greater than 50%. 3) Kaelin index: (p< 0.0001) was directly correlated with fracture risk but no cutoff could be identified.

For an 80 – 100% risk of fracture, the cyst must have the following characteristics: width > 30 mm, height > 75 mm, cortical thickness < 2.4 mm, Kaelin index > 5.

For a 50% risk of fracture, the cyst must have the following characteristics: width > 24 mm, height > 55 mm, cortical thickness < 3 mm, Kaelin index > 3.

Conclusion: The Kaelin index is reliable but difficult to calculate in the consultation setting. Cortical thickness is a good indicator. Its predictive value can be improved by correlating the height of the cyst with its width. These measure can be obtained easily during consultation.

Purpose: The immature skeleton demonstrates a remarkable capacity for correcting residual deformations after fracture. Classically, a residual angle of less than 25° can be tolerated for distal fractures of the forearm in children. The degree of remodelling depends on the distance between the fracture line and the epiphyseal line, the time remaining before closure of the growth cartilage, the residual angle after reduction, and is orientation in relation to the motion of the adjacent joint. The purpose of the present study was to better define the upper limit for acceptable deformation by age in order to determine when surgical correction is indicated.

Material and methods: We reviewed the radiography files of 106 children with one or two fractures of the distal third of the forearm who had required closed reduction and brachio-antebrachial cast immobilisation. We measured the angle of deformity on the AP and lateral views after reduction, at six weeks and at three, six, and twelve months after trauma. The series included 79 boys and 27 girls, mean age 8.5 years (range 2.5 – 15). Twenty-five fractures were epiphyseal fractures and 81 were metaphyseal fractures.

Results: Remodelling was nearly complete one year after fracture in most cases, especially in younger children and more distal fractures. Salter I or II fractures remodelled very rapidly, within four to five months of trauma. This remodelling was mainly achieved by apposition-resorption in the metaphyseal area by reorientation of the epiphyseal line. For the metaphyseal fractures, rate of remodelling was inversely proportional to the distance between the fracture line and the growth cartilage. Remodelling was greatly perturbed in case of open fracture requiring surgical reduction and in case of secondary infection.

Discussion and conclusion: These data show that posterior inclination can be tolerated up to 30° for children under eight years of age and up to 25° between eight and ten years and up to 20° at prepuberty. Knowledge of these limits for distal fractures of the forearm is important for proper management and can be helpful in reducing the number of primary or secondary reductions under general or locoregional anaesthesia.

Purpose: Continuous monitoring of the interstitial pressure of muscle compartments is a useful method for preventing compartment syndrome. The perfusion pressure is the key measurement (difference between the arterial diastolic pressure and the interstitial pressure). It should always remain above 30 mm Hg. Our postoperative monitoring data provided new insight into circumstances where there is a higher risk of compartment syndrome due to a fall in arterial diastolic pressure.

Material and methods: Twenty patients (13 boys and 7 girls) underwent continuous monitoring of the interstitial pressure of the anterolateral compartment of the lower limb. These children had undergone lengthening-realignment procedures, realignment procedures, or treatment of fracture. Mean age was 11.5 years. Preventive subcutaneous aponeurotomy was performed in 15 patients. The patients were monitored for a mean 55 hours. The interstitial pressure was noted every hour, in addition to pain on a visual scale, and the type and administration route of antalgesics. A risk condition was defined as perfusion pressure (diastolic arterial pressure – interstitial pressure) less than 30 mmHg.

Results: One or more episodes of low perfusion pressure (< 30 mmHg) were observed in eleven of the twenty patients, during the first five postoperative hours in five and during sleep and awakening phases in eight. Pain was not increased during these periods during which antalgesics were administered. The common denominator for these risk conditions was high pressure in the muscle compartment but low diastolic pressure. None of the children developed a compartment syndrome with sequela. Preventive aponeurotomy did not protect against the development of these risk conditions.

Discussion: These results provide new insight into the haemodynamic conditions occurring during the recovery period and point out the need for rapid recovery of an elevated diastolic arterial pressure. This would decrease the risk of compartment syndrome and also limit postoperative oedema.

Conclusion: Immediate postoperative monitoring of the interstitial pressure demonstrated that the risk of compartment syndrome occurs when the diastolic pressure is low, that is during postoperative awakening and periods of sleep in children given antalgesics.

Purpose: Reflex dystrophy is a poorly understood condition which must not go unrecognized due to the invalidating consequences.

Material: Twenty-four children aged seven to fifteen years were treated for reflex dystrophy since 1998. The foot or ankle was involved in 73% of the cases, generally secondary to ankle sprain. The diagnosis was established on the basis of the clinical presentation and on bone scintigram data obtained in all cases. Mean delay to diagnosis was 17.9 weeks, one case being diagnosed at 2.5 years.

Methods: An intravenous block (xylocaine and buflomedil) using a low-pressure tourniquet and without anaesthesia was performed in 23 patients. The local anaesthesia allowed gentle manipulation of the stiff joint so the child could visualise renewed mobility. The block was associated with gentle physical therapy, balneotherapy, and psychological support.

Results: The intravenous block was immediately and totally effective in 78% of the cases, the child being able to walk with full weight bearing without pain. Recurrence rate was 17%, occurring within the first month after the block in 80% of the cases.

Discussion: Diagnosis of reflex dystrophy is basically clinical, but the scintigram supported the diagnosis and enabled better localisation of the anatomic region involved. We have abandoned first line calcitonin which has demonstrated less satisfactory results than intravenous blocks. Combining a local anaesthetic with a low-pressure tourniquet improves patient comfort without the inconvenience of general anaesthesia.

Conclusion: Care must be taken to no overlook reflex dystrophy in children and adolescents. First intention use of an intravenous block significantly shortens the clinical course allowing the child to resume physical activities.

Purpose: Assessment of orthopaedic or surgical treatment in children with cerebral palsy is essential. For the lower limb, the main objective is to improve walking. Gait and control of static and dynamic posture are closely related. In this preliminary study, we attempted to determine whether treatment of pes equin which perturbs gait and equilibrium improves control of static and dynamic posture.

Material: Four children with spastic diplegia, one boy and three girls, aged five to fourteen years participated in this preliminary study. These children had unilateral or bilateral fixed or dynamic pes equin requiring medical (injection of botulinic toxin and/or lengthening casts) or surgical (aponeurotomy of the gastrocnemius) management.

Methods: Balance Master® was used for the posturographic evaluation. This system uses a force platform for calculating the vertical component at the centre of downward force on the feet. Five tests were used: distribution of body weight, stability in different sensorial conditions, single stance stability, limits of stability, rhythmic balancing movements. These tests were performed during the month preceding treatment and two and four months after treatment.

Results: For distribution of body weight, two children clearly improved after treatment. For the stability test in different sensorial conditions, all children showed improvement. There was no real improvement in the single stance test but two children who had had a unilateral treatment exhibited degradation on the untreated side. The rhythmic balancing movements test revealed an improvement in directional control in three of the four children.

Discussion and conclusion: This preliminary study demonstrated the feasibility of obtaining an easily implemented patient-friendly assessment of static and dynamic posture control in very young children with cerebral palsy. The Balance Master® system appears to be an interesting research tool for assessing posture control before and after treatment and might also be a useful rehabilitation tool.

Purpose: Unless exposed to stress, bone undergoes lysis. Osteoconduction is not observed in hydroxyapatite in contact with dead bone. We wanted to know whether bone blocks positioned on metal back cups in patients with total hip arthroplasty for acetabular dysplasia are destroyed lysis or “adhere” to the hydroxyapatite.

Material and methods: The series included 22 bone blocks in 21 patients with low weight-bearing displacement (n=10), high weight-bearing displacement (n=6), high non-weight-bearing displacement (n=6). Mean follow-up was six years (17 patients > 5 years).

Technique: all blocks were fashioned with autologous bone. The size of the cup, and thus the volume of the bone block, was determined by the largest anteroposterior diameter compatible with the desired position. The block was fashioned with a trial cup in place. The definitive cup was inserted separately then lag screwed to the bone block.

Implants: twenty-two titanium cups (3 mm) with hydroxyapatite surfacing, bone block width: approximately 28° from the centre of the prosthetic head.

Cup position: native acetabulum (n=11), neoacetabulum (n=11).

Results: Complications were : sciatic paresia (n=0), displacement (n=0), shift in cup position (n=1 at day 21). Partial lysis of the bone block was observed but there was no case of total lysis.

Titanium-hydroxyapatite-block adhesion: no lucent line was visible in 17 cases at more than five years. There were no cases of bony nonunion.

Discussion: Are grafts necessary with a metal back cup? The cup is slightly exposed in some primary degenerative hips but all goes well for ten years without a bone block. At what point would cup “exposure” require a bony support? As autograft material is available, it would appear inappropriate to not use it, especially since the lack of lysis suggests grafts are useful. All bony structures behave in an intelligent manner: an oversized bone block undergoes lysis but the part under stress above the cup becomes more dense.

Conclusion: Autologous bone blocks placed on metal back cups are not destroyed by lysis. The bone-hydroxyapatite couple adheres normally. Autologous bone blocks above metal back cups behave intelligently, like blocks inserted above cemented polyethylene cups.

Purpose: The double mobility of the G. Bousquet cup—head-polyethylene,polyethylene metal cup—considerably reduces the risk of total hip arthroplasty displacement.

Material and methods: We observed seven cases of “intra-prosthetic” displacement in patients with this type of cup. Progressive wear of the polyethylene retention ring allowed displacement of the femoral head. These displacements occurred in six patients (one bilateral case) aged 43–58 years, on the average ten years after the implantation (range 3.5 – 15 years).

All patients underwent revision.

Results: The polyethylene retention ring was worn in all cases allowing the femoral head to escape. Revision surgery was performed very early in six hips to change the modular base and the polyethylene ring and re-establish retaining capacity. A satisfactory result was achieved in all cases. One patient required revision five years later to change the prosthesis subsequent to haematogenous infection. Another patient underwent a late revision to change the modular base and the entire cup of a press fit implant. This hip was in excellent condition but revision was decided on because of four dislocations.

Discussion: Intra-prosthetic displacement of the polyethylene head of a double-mobility cup is exceptional in our experience. Wear of the retention ring is favoured by different elements: 1) direct phenomena: neck and head diameter causing early contact between the neck and the cup; 2) indirect phenomena: factors limiting the mobility of the polyethylene metal cup couple (fibrosis, repeated interventions, ossification).

In our experience, intra-prosthetic displacement occurs more readily in patients with favouring conditions (alcoholism, muscle deficiency, psychiatric disorder, obesity) observed in six of our seven cases.

Conclusion: Intra-prosthetic displacement of a double-mobility cup is a possible but exceptional complication requiring a technically simple revision. Some teams use this type of cup systematically and for us is an essential element for preventive treatment in high-risk patients and for curative revision of recurrent dislocation.

Purpose: Amstuz introduced the notion of a lever arm ratio to describe the relationship between the abductors and weight in arthroplasty. He demonstrated that patients may limp if defective lateralisation produces a low lever arm ratio. We analysed a continuous series of arthroplasty patients with excellent outcome at one year to compare restoration of lateralisation with the preoperative status. We also performed the same analysis in a series of patients who limped after arthroplasty, excluding cases with classical causes of failure. We then compared these two series.

Material and methods: We had a series of 100 arthroplasties with excellent results at one year. These patients had undergone unilateral arthroplasty and had a healthy contralateral hip. The centre of the arthroplasty head was identified on preoperative and one-year AP x-rays of the pelvis (same magnification). We measured the lateralisation in relation to the femoral axis. The position of the cup was measured with a U ratio. Results were expressed in percent restitution of the preoperative status. Amstutz’s lever arm ratio was also measured. Finally, we measured the distance between the pubic symphysis and the outermost point of the femur on the prosthetic and healthy side.

We also had a second population of twelve patients presenting persistent limping at one year with no objective cause. The same parameters were measured for this population.

Results: We found that we had achieved only partial restitution of the initial lateralisation and had a tendency to medialise the acetabulum. The restitution of lateralisation was significantly different between the series with excellent outcome and the series with limping.

Discussion: Deficient lateralisation appears to be a factor involved in persistent limping. There is a threshold for restitution of lateralisation; limping is always observed under this threshold. Data in the literature reveal a very wide variability in lateralisation. It would thus appear important to restore the initial lateralisation to avoid limping; this has led us, like others, to use lateralised implants for certain patients.

Purpose: Nonunion of the trochanter after total hip arthroplasty using the transtrochanteric approach is a serious complication. Incidence is estimated at 3%. Failure after simple cerclage reaches 40%. A plate was therefore designed specifically for fixation of trochanteric fractures. The purpose of this retrospective analysis was to assess outcome in a continuous series of trochanteric fractures treated with this plate.

Material and methods: The series included 72 nonunions in 71 patients treated between 1986 and 1999. Mean age was 66 years. Most of the arthroplasties had been performed for primary degenerative joint disease or for hip dysplasia. The time interval between artrhoplasty and treatment of the nonunion was eight months on the average. The trochanter was fixed with a plate alone in 47 hips and in combination with a frontal wire in 25. The primary outcome criterion was trochanter healing scored as: union (pain free hip, radiological fusion and stability), nonunion (lack of radiological fusion and/or presence of an instability), and doubtful union (moderate pain, no instability, radiological fusion difficult to affirm).

Results: Mean follow-up was 47 months (range 12 – 14). Mean functional score at last follow-up was 15/9 compared with 13.5 preoperatively (paired test, p < 10–4) with 51 unions, 12 nonunions and 9 doubtful unions. Among the factors studied, trochanter fixation technique was the only factor predictive of outcome. Results were as follows for plate fixation alone: union 62%, doubtful union 13% and failure 25%. For hips with wire and plate fixation, the results were union 87.5%, doubtful union 12/5%, failure 0%. The difference was highly significant (chi-square, p = 0.006) in favour of wire-plate fixation of trochanteric fractures.

Discussion and conclusion: This study leads to the conclusion that the treatment of choice for trochanteric nonunion is wire-plate fixation which provides more than 90% good and very good results.

Purpose: We compared two series of total hip arthroplasties (THA) at more than 12 years. The only difference between the two series was the nature of the femoral head: 28-mm zincronia head versus 32-mm alumina head.

Material and method: All THAs were performed during the same period (1988–1990) and the polyethylene inserts, the femoral components, the surgical cement and the operator were the same for both series. Patient age and mean weight were the same for the two series of 40 Zir/PE and 62 AL/PE implants: 98 and 63 years and 72 and 73 kg respectively. Implant survival, polyethylene wear on AP and lateral x-rays, and Merckel osteolysis were studied.

Results: Three revisions were required at eight, ten and eleven years in the Zir/PE group. No revisions were required in the Al/PE group where there were no signs of loosening on the radiograms.

During the first four years, polyethylene wear appeared to be the same in the two series. Beyond the fifth year, penetration of the alumina heads exhibited a regular mean 0.07 mm progression per year. Beyond the fifth year, penetration of the zircona heads accelerated reaching a mean 0.4 mm per year at twelve years. Mean volumetric wear of the polyethylene cups was 1360 mm3 for the zircona heads and 755 mm3 for the alumina heads. Osteolysis was seen as a defected facing the merckel and measured 2.5 cm2 for the Zir/PE couple and 0.35 cm2 for the Al/PE couple. The differences between the two series in linear penetration, volumetric wear, and osteolysis were significant (p < 0.05). The three zircona heads that were removed showed partial transformation from the tetragonal phase to the monoclinical phase (19%, 25% and 30%) and a roughened surface which was not sufficient to explain the polyethylene wear. Abnormal wear was explained more by loss of spherical shape and the greater volume of the zircona heads, probably related to a modification of the crystalline phase (change from the tetragonal to the monoclinical phase usually is associated with a 3% increase in volume). Analysis of the fingerprints left on the morse code of the zircona heads suggest the change in volume of the zircona heads was associated with a change in the contact between the morse cone and the zircona head over time. Analysis of the explanted cups showed wear with delamination in two cases. For one of the implants, the polyethylene insert was deformed exhibiting a fusion aspect corresponding to abnormal increase in temperature.

Discussion and conclusion: The zircona implants manufactured more than twelve years ago probably do not meet current manufacturing standards. Nevertheless, the changes observed in the explanted pieces would suggest they are related not only to the manufacturing process but also to the material itself.

Purpose: There has only been one reported series of 30 cases of greater trochanter fracture during total hip arthroplasty and 26 of these were postoperative discoveries. We evaluated the frequency of this event and its postoperative consequences.

Material and methods: Among our series of 1171 total hip arthroplasties performed between 1985 and 2000, 38 patients (3.2%) with greater trochanter fracture were identified (mean age 63 years). Osteosynthesis was performed in all cases. Thirty-one fractures were observed during primary arthroplasty and seven during revision procedures.

Results: Eighteen patients had a favouring condition: corti-costeroid therapy,alcoholism,osteoporosis,diabetes,Paget, ablation of trochanteric material, periprosthetic osteolysis. The anterolateral approach was used in 22 and the posterolateral approach in 16. The fracture occurred along the access route in four (material removal or prefracture situtation), at removal of a previously implanted stem in two, and during implantation in 32. Twelve different stems were involved but a screwed stem was involved in 18 cases, i.e. 10% of all implanted screwed stems, while this complication only occurred in 1.2% of other implanted stems. Immediate weight bearing was authorised in 27 patients and deferred three weeks to three months in eleven. There were two deaths, so follow-up data was available for 36 hips: we observed anatomic bone healing in 22, deformed calluses in five and nonunion in nine, including two cases with infection (three revision procedures were required). Pain persisted at two months for eleven hips and limping persisted for ten (eight nonunions).

Discussion: Prostheses with a large metaphyseal component were involved in the majority of the fractures. The surgical approach was not incriminated. When well stabilised, trochanter fractures healed well. Nonunion, often announced by persistent pain, is an important risk in patients with osteoporosis and a poorly stabilised fracture. Although all cases of nonunion were observed in patients with deferred weight bearing, this criterion is simply the expression of the surgeon’s apprehension in case of less than satisfactory fixation.

Conclusion: Because of the deficient bone stock, which explains the higher rate of nonunion, fracture of the greater trochanter cannot be considered in the same light as a planned osteotomy. Prevention requires choosing a less cumbersome metaphyseal component in patients with favouring conditions. Osteosynthesis must be performed with particular care in order to obtain rapid healing and good functional outcome.

Purpose: The purpose of this retrospective study was to assess clinical and radiological outcome at ten years follow-up at least in a continuous series of total hip arthroplasties performed in patients with aseptic necrosis of the femoral head.

Material and methods: The series included 122 arthroplasties performed between January 1980 and December 1996 in 96 patients (26 women and 70 men), aged 50.8±13.3 years (range 21–85 years). The underlying cause was essential necrosis in 40.6%, cortocosteroid threapy in 19.8%, chronic alcoholism for 17%, trauma for 12%, and another medical cause for 10%. The Ficat and Arlet classification was grade IV 80 hips, grade III 42 hips. All arthroplasties were performed via the transtrochanteric approach. Cemented Charnley-Kerboull implants were used with a metal-polyethylene couple in all cases. The Merle d’Aubigné score was used to assess functional outcome. Cup wear was measured according to Livermore. Actuarial survival curves were calculated.

Results: Follow-up was greater than ten years for all patients (mean 13±2.6 years, range 10–21 years). At last follow-up 59 patients (75 hips) were living and had not undergone revision and seven patients (seven hips) had undergone revision of the acetabular and/or femoral component. Twenty patients (24 hips) had died and ten patients (16 hips) were lost to follow-up. Revision procedures were performed for periacetabular osteolysis in one hip, infection in one hip, and acetabular loosening in five hips. Three patients experienced luxation or subluxation. The mean preoperative function score was 11 (range 5 – 16) compared with 17 (14–18) at last follow-up (p < 0.05). Clinical outcome was good or excellent in 95% of the patients and fair or poor in 5%. Mean overall cup wear was 0.965 mm (0–5) for non revised hips. Lucent lines were found around eleven acetabular implants and six femoral implants. Cumulative survival, considering revision as failure, was 88.5% at 15 years (95% confidence interval 80.2 – 96.9%).

Discussion and conclusion: The results of this series lead to the conclusion that low-friction total hip arthroplasty is the treatment of choice for advanced stage femoral head necrosis.

Purpose: Treatment of Ficat III and IV femoral head necrosis is a serious challenge and a controversial issue due to the young age of the patients and disappointing results obtained with total hip arthroplasty (THA). We reviewed our experience with the cemented adjusted cup to identify factors leading to surgical revision and assess long-term clinical outcome.

Material and methods: Sixty hips presenting necrotic heads were treated by cemented adjusted cups. Mean age of the patients was 33.6 years (range 18–51); 23% women and 77% men. The Ficat classification was: grade II 6%, grade III 85%, grade IV 9%. Mean necrotic Kerboull angle was 192°. In addition, the status of the acetabular cartilage was recorded at surgery: grade I normal 17%, grade II fissuration 30%, grade IIIA fibrillation without osteophytes 28%, grade IIIB fibrillation with osteophytes 10%, grade IV partial erosion reaching subchondral bone 10%.

Results: At mean follow-up of 7.8 years (range 1 – 21 years), there were no cases of dislocation, femur neck fracture, or osteolysis. Mean UCLA score showed significant improvement in pain (from 4.5 to 8.1), walking (6.1 to 8.8), function (5.3 to 7.6), and activity (4.2 to 5.8). Five-, ten-, and fifteen-year survival rates were 81, 57, and 40% respectively. Fifteen hips required THA, twelve for acetabular cartilage wear, one for femoral loosening, and one for infection. A positive correlation (p = 0.005) was observed between the duration of signs preoperatively and degradation of the acetabular cartilage, suggesting a relationship also with shorter prosthesis survival. The Kerboull necrosis angle and Ficat grade were not correlated with prosthesis survival.

Discussion: Survival of the adjusted cup is better when symptoms have been perceptible for less than one year, probably because the acetabular cartilage is less damaged. These results are better than those with other conservative solutions such as osteotomy or vascularised graft which do not reach 80% survival at five years and which provide less effective pain relief. If necessary, conversion to a THA can be performed without compromising clinical outcome.

Purpose: Fracture of alumina implants is a rare cause of total hip arthroplasty (THA) failure. Over the last twenty years, improvement in the design of ceramic implants has helped reduce this risk. We observed five cases of alumina implant fracture over the last year. The purpose of this work was to analyse these recent events and to examine our experience to search for an explanation.

Material and methods: Between 1976 and 2002, eleven patients, five women and six men, mean age 57 years (range 32–87 years) required revision surgery for fracture of an alumina component. The time interval from primary surgery to revision was 36.5 months (range 7 – 106 months). An alumina-alumina couple was involved in nine cases and an alumina-PE couple in two. The primary THA used a press-fit metal backed alumina cup for five hips, a cemented alumina cup for three hips and a massive press-fit alumina cup for one. The alumina head measured 32 mm for ten hips, 22.2 mm for one. The femoral stems were cemented in seven cases, and hydroxyapatite surfaced in four. The acetabular component was involved in four cases and the femoral head in seven.

Results: Identified causes of ceramic implant fracture were: high-power trauma (insert) (n=1), insufficient head diameter (n=1), and defective head match (n=1). For the eight other fractures, involving three insets and five heads, no triggering factor could be identified. The three insert fractures involved two 50-mm cups and one 52-mm cup. Insert design had been changed before these fractures. Mean time from insertion to fracture was 12 months (range 8.5–15 months) in these cases.

Discussion: To our knowledge, all reported cases of ceramic implant fracture have concerned the prosthetic head. The present series demonstrates a recent development, fracture of acetabular implants. It is hypothesised that these fractures could be explained by an insufficient cup diameter associated with a recent change in the design of the metal-backed flush ceramic insert. These inserts have been modified and now have an “overhang” design associated with a thicker layer of ceramic for the smaller cup diameters. These accidents remain rare but justify careful surveillance, particularly during the first postoperative year.

Purpose: We report the clinical and radiological outcome observed with Charnley total hip arthroplasties in a series of patients aged less than 60 years followed for at least 25 years.

Material and methods: This retrospective analysis included 141 consecutive total hip arthroplasties performed between 1972 and 1975 with a Charnley implant. The same surgeon used the same technique for all implants. All of these patients had been followed regularly for at least 25 years. We recorded radiographic measures of polyethylene cup wear and its impact on prosthesis life. We tested the influence of different factors on the development of femoral or acetabular loosening. Survival curves were calculated for acetabular and femoral components.

Results: At last follow-up 28 prostheses were still in place, 44 had undergone revision, 42 were lost to follow-up and 27 patients had died. At last follow-up, including the revised hips, joint function was considered, good, very good or excellent in 86% of the cases (merle d’Aubigné score 15 – 18 points). Polyethylene wear was 0.12 mm/year. Merkel osteolysis was observed in 50% of the cases.

Discussion and conclusion: This work demonstrates the good functional outcome provided by Charnley total hip arthroplasty. The wear and loosening rates were higher than observed in older patients. Prognosis depends on polyethylene wear and its biological consequences.

Purpose: Scoliosis is a three-dimensional deformation of the spinal column. Modern surgical techniques have attempted to address this 3D component of the problem but pre- and postoperative measurements lack precision. A solution is stereoradiographic 3D reconstruction providing 1.1 mm precision for vertebral shape and 1.4° precision for axial rotation.

Material and methods: Ten patients (seven adolescents and three adults) with idiopathic scoliosis (mean 56°, range 36°–78°) were treated with an in situ arching method. A calibrated teleradiogram (AP and lateral view) was obtained before and after surgery. The spinal columns were reconstructed by stereoradiography. Six rotation angles were measured in the three planes for each vertebra and each intervertebral space, taking into account the curvatures and their apical and junctional zones.

Results: Preoperatively, for thoracic scoliosis, measurements were: mean vertebral axial rotation (VAR) measured at the apex = 20°; mean lateral axial rotation (LAR) of the junctional zones = 30°; mean intervertebral rotation (IVR) = 10°. Depending on the curvatures, in situ arching yielded a 52–60% correction of the VAR at the apex, and 78–79% correction of the junctional zones. VLR of the junctional zoenes was improved 58–74%. Intervertebral sagittal rotation (ISR) at the summit (kyphosis) was improved 5.5° on the average.

Discussion: Unlike computed tomoraphy where scans are obtained in the supine position, three-dimensional reconstruction of the spinal column enables a precise analysis of the loaded spine. Improvement was significant in the frontal plane with 18.3° and 21.4° improvement of the VLR for the thoracic and thoracolumbar junctional zones respectively, compared with the rod rotation where the peroperative stereophotogram showed a 9.6° and 8.6° gain respectively. There was a real improvement in VAR, differing from the literature where the rotation of the rod appears to be less pronounced.

Conclusion: Three-dimensional reconstruction of the spinal column enables a segmentary analysis of scoliosis deformations. In addition, by enabling a view of the spinal column in all directions, angle measurements can be made with precision allowing repeated measurements and comparisons. This technique demonstrated the efficacy of in situ arching in improving vertebral rotation.

Purpose: Alumina resistance to wear is now well established. In the eighties, improvement in manufacturing processes and implant design led to a significant reduction in the risk of fracture but failure of acetabular fixation remained a cause leading to revision. The purpose of this work was to present our results with a consecutive series of press-fit cementless metal backed alumina-alumina THA implanted between 1990 and 1992 in patients aged less than 55 years.

Material and methods: The series included 62 patients and 71 hips. Mean age at surgery was 46 years (range 21 – 54). A cemented titanium femoral stem with a 32-mm alumina head was implanted with a press-fit metal-backed cup with an alumina insert. Three patients (4 hips) died. Four hips required revision for infection (n=1), unexplained pain (n=1), fracture of the alumina head (n=1), and aseptic cup loosening (n=1). At nine years the survival rate was 93.7% taking revision for all cause as the end point and 98.4% taking revision for aseptic loosening as the end point.

Results: Fifty patients (57 hips) were reviewed with at least five years follow-up (mean 8 years, range 6–11 years). According to the Postel-Merle d’Aubigné score, functional outcome was excellent or very good in 96% of the patients. A minimal partial lucent line was observed around 38% of the cups, mainly in zone III and one cup exhibited a complete line measuring < 1 mm. Isolated osteolysis of the femur was observed in one hip. There was no case with acetabular osteolysis or implant migration.

Discussion: Combining a cemented stem with a pressfit metal backed cup has provided very satisfactory mid-term results in these active patients. Use of a press-fit hemispheric cup has been found to be a reliable fixation method for alumina cups and improves results of Al-AL THA significantly. In light of the excellent resistance of the alumina cups against wear, these results can be expected to continue for a long period.

Purpose: We report a retrospective continuous series of 107 total hip arthroplasties using a hydroxyapatite-coaated cup followed for a mean 9.67 years. We studied implant stability and component wear.

Material and methods: One hundred total hip arthroplasties were performed between January 1991 and January 1992. The series included 67 women and 40 men operated by the same surgeon who used the same Alizé cup and Aura cementless stem. Mean age at surgery was 66.5 years (range 30–85). Mean follow-up at review was 9.6 years. We retained 63 hips for analysis excluding 17 deaths, 16 patients lost to follow-up, 10 patients who could not be followed correctly, and only one implant ablation (0.9%). The implant was a first intention prosthesis in 90.7% of the cases and a second operation to replace a loosened primary prosthesis.

The Postel Merle d’Aubigné score was used to assess clinical outcome and all patients responded to a self administered questionnaire. Radiographically, we searched for signs of instability (tilt, displacement) and implant wear using precise digitalized measurements on successive digitalized x-rays with MetrOs software. We searched for qualitative radiological signs of bone reaction in contact with the implant.

Results: The overall PMA score improved from 10.63 preoperatively to 16.98 at the intermediary 5-year follow-up and was 15.77 at the 10-year follow-up. Satisfactory results were obtained in 93.9% of the patients at five years and 98.5% of the patients (64 hips) at 10 years. There were two fractures of the ceramic head after direct fall on the greater trochanter (requiring changing the femoral implant, the head and the polyethylene insert). There was one cup loosening at 9.5 years with verticalisation of the implant in an active athlete. Analysis of the x-rays did not demonstrate any abnormal condensation or lucent lines. Bony defects were observed in one case. The MetrOs radiographic data were available for 55 hips. At five years, mean wear was 0.53 mm, which increased to 0.76 mm at ten years (range 0.16 – 2.24 mm). Cup ascension was 0.15 mm at five years and 0.76 mm at 10 years. Mean cup tilt was 46.2° immediately after implantation and varied a mean 0.7° at five years and 1° at ten years.

Discussion and conclusion: This radioclinical study at ten years follow-up demonstrates that the hydroxyapa-tite surfaced Alizé implant is stable over time. The clinical results in this study were satisfactory with minimal regression of the PMA score related to patient ageing. The x-rays analysed with a rigorous and precise measurement instrument provided reassuring results. We discussed the one cup loosening and the clinical course of the two patients who underwent revision procedures after trauma-induced fracture of the ceramic head.

Purpose: Cervical laminoplasty has been used for the treatment of cervical arthrosic myelopathy in Japan. The purpose of this work was to assess clinical and radiological outcome at more than two years follow-up.

Material: Thirty-one patients underwent laminoplasty of three levels or more for cervical arthrosic myelopathy and were reviewed more than two years after surgery.

Methods: The Japanese Orthopaedic Association score was used to assess function preoperatively and at last follow-up. Preoperative and last follow-up standard strict lateral and flexion and extension x-rays of the cervical spine were available for all patients. The curvature was assessed on the lateral view in the neutral position (C2–C7 Cobb angle). Overall mobility was assessed on the dynamic views.

Results: The mean preoperative score was 9.7, improving to 138 at last follow-up (p < 0.0001, paired t test). Mean relative gain was 52.9%. The mean Cobb angle was 17° preoperatively and 8.9° at last follow-up. Cervical spine curvature and overall mobility had no influence on the score at last follow-up. The postoperative Cobb score was only influenced by the preoperative angle (p < 0.0001). There were no reoperations for instability.

Discussion: Guigui has demonstrated that mean loss of cervical lordosis in a series of extended laminectomies was 14°. In our series, mean loss of cervical lordosis was 8.1°. Laminoplasty enables a better preservation of cervical lordosis than laminectomy. Guigui also reported three patients requiring reoperation because of an unstable spine after laminectomy. Inversely, we did not have any cases requiring reoperation. During laminoplasty, a gutter is fashioned in a medial quarter of the articular masses to open the lamina, producing their fusion. This unexpected fusion diminishes overall mobility but also has a less destabilising effect on the spine than laminectomy.

Purpose: A retrospective study of 17 fractures of the cervical spine in patients with ankylosing spondylitis is reported. The purpose of this study was to search for risk factors of fracture in ankylosing spondylitis an to assess treatment outcome.

Material and methods: Seventeen patients treated between 1982 and 2201 were reviewed with a mean follow-up of five years. There were three women and fourteen men, mean age 60 years at trauma. Fifteen patients underwent surgery and two were treated orthopaedically.

Results: This group of patients with ankylosing spondylitis with fracture of the cervical spine was homogeneous: age 60 years, disease duration 30 years, fracture due to fall. The fracture was at the C6/C7 level in 47% of the patients where the lever arm is the greatest and also a level that is difficult to explore, explaining the late diagnosis in 35% of the patients. Sixty percent of the patients were in Frankel classes D or E and 23% in classes A or B. Anterior fixation was used for 14 patients, posterior fixation in one. A long osteosynthesis involving several levels was used in all cases. Major kyphosis had developed in three patients after fracture which was not recognised initially; at fixation, an anterior wedge graft was inserted in the fracture line for correction. Mean correction was 20° with good restoration of the lordosis and rehorizontalization. Bone healing was achieved in all operated patients without loss of the reduction of the kyphosis at last follow-up. The neurological status did not worsen in any patient. Anterior fixation was insufficient to reduced an old fracture-dislocation in one patient who required posterior decompensation. Orthopaedic treatment was used in two patients: the first (Frankel A) died at two months and the second healed with a 10° aggravation of the cervical kyphosis. All the Frankel A and B patients in this series died.

Conclusion: All patients with severe neurological involvement died. The anterior approach, used alone, provided good stabilisation of the cervical spine. For the patients without neurological involvement, reduction of the cervical kyphosis should be associated with a stabilisation procedure in case of fracture with kyphosis.

Purpose: Several techniques have been proposed for C1-C2 fusion. The anterior transoral technique is the most direct approach but at the cost of major risk of infection. The posterior approach allows wiring (Gallie technique) or direct atloidoaxoid screw fixation (Magerl technique). The retrosternomastoid bilateral approach (Du Toit technique) allows direct screwing in the lateral masses. The rate of nonunion reported in the literature is high for wiring techniques. Biomechanical studies have demonstrated the mechanical superiority of trans-articular screwing which has been confirmed in clinical series. The purpose of the present study was to describe a modification of the Du Toit technique and describe results in a short series.

Material and methods: This modification of the Du Toit technique consists in an abrasion of the C1 lateral mass at its origin enabling the penetration of a Cloward curette to create a stable introduction point for the drill bit and thus avoid slippage forward as can occur with the conventional technique. The screw is directed towards C2, in a strict frontal plane. The obliquity depends on the room allowed by the mastoid. The drill bit should cross both corticals of the inferior facet of C1 and the superior facet of C2. The screws must cross in a coronal plane just under the odontoid. Fusion of the C1-C2 lateral masses is achieved by abrasion and grafting.

We have used the modified Du Toit technique for C1-C2 arthodesis in four patients with rheumatoid arthritis, fracture of the odontoid, an odontoid bone, and isolated degeneration. The procedure was a first intention treatment for the patient with primary degeneration, and a second intention procedure for the others who had developed nonunion after wiring.

Results: Mean hospitalisation was six day. Operative time was 2 h 10 min. Mean blood loss was 200 ml peroperatively and 120 ml postoperatively. None of the patients had developed nonunion or mechanical failure at a mean follow-up of 2.7 years (range 1 – 5 years). Operative complications included one case of venous bleeding which was treated with vascular clips and two cases were the lateral mass of C1 was weakened requiring cementing. There was one early postoperative neurological complication with hypoaesthesia of the hemitongue that regressed spontaneously. None of these complications produced sequelae.

Conclusion: The advantages of the modified technique for lateral screw fixation of C1-C2 is the improvement in the entry point for the drill bit allowing an optimal screw position and a stable drilling to achieve good mechanical fixation and certain union.

Purpose: The biomechanical behaviour of the cervical spine was studied in vitro with an optoelectronic system in order to better understand its physiology.

Material: Twenty fresh cervical spines (occiput-D1) from fourteen men and six women, mean age 66.5 years, were sterilised with ß radiation (2.5 Mrad) and stored at −24°C then studied after slow thawing and excision of the paraspinal muscles.

Methods: Three-point reflecting markers were rapidly attached to each vertebral segment (4 or 5 vertebrae). The inferior vertebra was blocked. Six pure moment couples (2 N.m maximum, 10 increments) were applied in the three anatomic planes using a loading device lodged on the superior vertebra. Displacements were measured with the VICON 140 using a kinematic software.

Results: The three-dimensional behaviour curves of each functional unit (FU) were recorded for each solicitation to analyse the principal movement and coupled movements (maximum mobility, neutral zones, rigid zones, rigidity). Mean maximal flexion-extension movements were C0/C1= 28.7°; C1/C2 = 22.3°; C2/C3 = 7.3°; C3/C4 = 10.6°; C4/C5 = 13.8°; C5/C6 = 13.4°; C6/C7 = 10.8°; C7/T1 = 6.4°. Maximum overall lateral inclinations were: C0/C1= 8.7°; C1/C2 = 9.3°; C2/C3 = 8.7°; C3/C4 = 6.7°; C4/C5 = 10.5°; C5/C6 = 12.2°; C6/C7 = 8.6°; C7/T1 = 5.7°. Maximal overall axial rotations were: C0/C1= 11°; C1/C2 = 71°; C2/C3 = 9.5°; C3/C4 = 10.8°; C4/C5 = 12.3°; C5/C6 = 9°; C6/C7 = 5.6°; C7/T1 = 5.7°. All the FU exhibited flexion-extension movement. Lateral inclination coupled important controlateral rotation for C1/C2 and minimal ipsilateral rotation (< 10°) in the lower FU of the cervical spine. Axial rotation of the C1/T1 functional unit was coupled with homolateral rotation (< 10°).

Discussion: Our experimental protocol provided precision of < 1° and good reproducibility allowing simultaneous three-dimensional analysis of the spinal functional units. Making measurements without direct contact is particularly useful for the cervical spine. Our results are within the experimental corridor defined by Goel, Panjabi and Wen.

Conclusion: This work on a large number of functional units adds further support to data in the literature concerning the biomechanical behaviour of the cervical spine. Our protocol could be applied to analyse the impact of surgical procedures used for the cervical spine, particularly for the evaluation of new fixation systems or prostheses.

Purpose: Fat or marrow embolism during or after bone and joint surgery is a serious complication. We wanted to determine the incidence and circumstances of peroperative embolism in patients undergoing lumbar spine surgery with and without instrumentation.

Material and methods: Sixty adult patients with degenerative lumbar spines underwent peroperative and early postoperative transoesophageal ultrasonography. The lumbar procedure involved instrumentation with insertion of pedicular screws in 40 patients.

Results: Moderate to severe signs of embolism (Pitto classification grade 2 or 3) were observed in 80% of the patients who underwent instrumentation procedures but in none of those who had not been instrumented (p < 0.001).

Discussion: Among the different procedures performed on the posterior lumbar spine, insertion of pedicular screws appears to be the leading cause of pulmonary embolism. The approach, laminectomy, discectomy, and bone abrasion do not appear to produce detectable embolism.

Conclusion: We consider that the observed embolic manifestations, also observed in intramedullar procedures, are potentially fatal after spinal surgery.

Purpose: Ankylosing spondylitis and Forestier hyperosteosis produces a fused vertebral column. The fused vertebrae can be considered like a “spine-bone” which has particular features different from those of the mobile spine. The purpose of this retrospective analysis was to investigate the clinical and radiological particularities of the spine-bone in order to reduce the delay to diagnosis.

Material and results: Forty-eight spinebone fractures were observed over a 17-year period by one practitioner. Twenty of the patients (mean age 62 years) had ankylosing spondylitis and 28 (mean age 81 years) had hyperosteosis. All of the patients were men. Twenty-five were victims of falls, eleven victims of traffic accidents, and six victims of sports accidents (all with ankylosing spondylitis). No notion of trauma could be identified for six patients. Sixteen fractures were diagnosed within 1 to 28 days. Forty-four patients had cord injury including 16 cases which developed secondarily. Four types of fracture were identified:

- type I = anterior opening fracture: 30 patients,

Fractures diagnosed late were four anterior opening fractures, eight “rasp line” fractures, and four “sawbone” fractures. A CT scan was obtained in all cases and an MRI in 30. Three compressive spinal extradural haematomas were diagnosed. Thirty-two patients died, 31 patients with spinal injuries due to decubitus-related complications and one by rupture of an aneurysm of the aorta.

Discussion: This series illustrates several points. Fracture without trauma is frequent. Diagnosis is made late. Fractures gone undiagnosed lead to neurological complications or nonunion. Diagnosis of “rasp line” fractures cannot be made on standard x-rays, leading us to order a scanner and/or an MRI in all patients with a painful ankylosed spine even if the standard x-ray does not show any fracture. Neurological and extradural haematoma are serious complications. Mortality is high in these debilitated patients. Knowledge of these exceptional fractures of the vertebral column is necessary to improve diagnosis and prognosis.

Purpose: There is growing concern about the effect of anterior fusion of the cervical spine on the adjacent levels. Long-term assessment is indispensable to understand the mechanisms involved in the degradation observed and to support the development of materials preserving discal mobility.

Material: Three hundred patients who underwent cervical arthrodesis were reviewed in 1996 forty months after the procedure for physical examination and an x-ray work-up including stress views. Cervical spine and radicular pain were assessed on a visual analogue scale.

Methods: A complete data set was available for 136 patients and a partial set for 34. Twenty-two patients only accepted a phone interview. The clinical outcomes in these three groups were not significantly different and the mean scores for these three groups were in the general average in 1996. Eight patients had died.

Results: Patients were divided into three groups by type of disease diagnosed preoperatively (trauma, degenerative spine, myelopathy). Mean follow-up was 102.5 months (range 84 – 180 months).

Trauma: Among the 42 patient reviewed again in 2001, mean deterioration in the subjacent segment increased from 21% in 1996 to 69% in 2001. Deterioration of the supraja-cent segment increased from 26% to 47.6%. Cervical pain remained moderate (20/100 in 1996 and 27/100 in 2001). Degenerative spine (root compression requiring simple discectomy or with arthrodesis or single-level corporectomy): Among the 42 patients reviewed again in 2001, deterioration of the subjacent segment increased from 57% in 1996 to 89% in 2001. Deterioration of the suprajacent segment increased from 22% to 41%. Cervical pain increased from 14/100 in 1996 to 41/100 in 2001.

Myelopathy: Among the 52 patients reviewed again in 2001, deterioration of the subjacent segment increased from 54% in 1996 to 81% in 2001 when there had been one or two corporectomies and from 40% to 70% beyond two. Deterioration of the suprajacent segment increased from 26% to 50%. Cervical pain remained moderate (18/100 in 1996 and 23/100 in 2001).

Conclusion: Although a statistical analysis was not possible because of the small number of patients and the large percentage lost to follow-up, these results confirm that fusion of the cervical spine accelerates the degradation of adjacent levels. Longer follow-up demonstrates that the trauma group “catches up” with the degenerative group.

Use of mobile materials should enable differentiating between effects related to the degenerative process and those induced by the arthrodesis.

Purpose: Single-segment wedge osteotomy is classically proposed to correct for kyphosis subsequent to ankylosing spondylitits. We analysed the usefulness of this technique for other indications (revision procedures for flat back and deformed calluses of the lumbar spine) by studying the overall sagittal balance of the spine and tilt of the sacrum.

Material and methods: Between 1980 and 1999, we retained 68 patients with complet clinical and radiological data (37 patients with ankylosing spondylitis and 31 patients with “post-operative” flat back, including nine trauma cases and 22 degenerative spines). Opening osteotomy was performed in the first 19 patients and closure osteotomy in the next 49. The correction level was L2L3 in 26 patients and lower in 42. Digitalised lateral views of the entire spine were obtained at minimum follow-up of three years to measure:

- posterior displacement of T9 (between the vertical line and a line joining the geometric centre of T9 and the femoral heads (normal 11±5°),

Results and discussion: The overall angle of local correction was 44° and the correction of T9 displacement was 30.6°. For the low osteotomies, the local correction was 49° and the T9 displacement was +28° (−2° to +26°). Tilt of the sacrum varied from 4° to 7°. Tilt of the sacrum was influenced more and more for lower and lower osteotomies. T9 displacement stabilised between 12° and 26° (mean 19°) irrespective of the osteotomy level, although the angle of local correction was greater (up to 60°). This discordance was explained by adaptation of the pelvis. Seven patients developed secondary functional kyphosis (limited hip movement preventing the necessary adaptation to the overall correction of the sagittal balance).

Conclusion: Single-segment spinal osteotomy remains difficult but offers very important correction possibilities affecting the position of the trunk and adaptation of the pelvis. The level for the correction must be chosen with care because it conditions final adjustment and function consequences affecting the pelvis.

Purpose: We report the clinical and radiological course in a continuous series of 194 patients treated by the same team between 1996 and 2001 for thoracolumbar fracture. Cotrel frame instrumentation and Boëhler corset immobilisation were used.

Material and methods: In this series of 65 women and 129 men, age range 16 – 77 years, we retained one year follow-up at least for inclusion in the study. More than 85% of the patients were retained for study and the final analysis concerned 150 patients who were contacted.

All patients were in Frankel class E. In compliance with the SOFCOT 1995 Symposium, the method described by Rosset and Laulin and the international classification described by Magerl were applied to pre-operative x-rays to search for the pathogenic mechanism involved. The radiological analysis was conducted on preoperative, immediate post-operative, 1-month, 3-month, and last follow-up x-rays. The course of spinal kyphosis and angular deformation of the trauma zone and the subjacent disc were analysed. In addition to the overall series, patients with limit therapeutic indications, according to the local kyphosis and trauma-induced regional angular deformation, were also studied.

Results: For the initial indication of choice, type A1 fracture, gain in reduction was minimal for the constraining treatment. For type A3 fractures, posterior displacement of the posterior wall was not a contraindication because the posterosuperior reduction could be achieved by ligamentotoxis in the majority of the cases The gain in correction of spinal kyphosis was greater in these patients. Nevertheless, for this type of fracture, spinal kyphosis greater than 15° was an implicit sign of a potential posterior distraction lesion where osteosynthesis might be indicated, especially since the USS fixator uses a parallel assembly and authorises short instrumentations.

Conclusion: The Boëhler technique is a safe, minimally invasive and low-cost method for the treatment of thoracolumbar spine fractures, which enabled 30% correction of the spinal kyphosis. This method retains its indications for type A fractures.