Inability to actively supinate the forearm makes common activities of daily living and certain vocational activities awkward or impossible to perform. A total of 11 patients with deficient supination of the arm underwent transfer of the tendon of flexor carpi ulnaris to the split tendon of brachioradialis with its bony insertion into the radial styloid left intact. Active supination beyond neutral rotation was a mean of 37.2° (25° to 49.5°) at a minimum follow-up of three years, representing a significant improvement (95% confidence interval 25 to 50, p < 0.001). Functional evaluation of the hand after this transfer showed excellent and good results in ten patients and fair in one.

The split tendon of brachioradialis as an insertion for transfer of the flexor carpi ulnaris appears to provide adequate supination of the forearm without altering the available pronation and avoids the domination of wrist extension sometimes associated with transfers of the flexor carpi ulnaris to the radial extensors of the wrist.

Reverse total shoulder replacement is a viable surgical option for Cuff Tear Arthropathy. Short term results have been promising. Longer term follow-up has demonstrated a high rate of scapular notching. This is attributed to mechanical impingement between the humeral cup and scapular neck when the arm is fully adducted. The long term sequelae of scapular notching are unclear but there is concern that it may compromise fixation of the glenoid component and affect functional outcomes.

Design modifications to address this problem include the newly available eccentric glenospheres and larger diameter glenospheres. These glenospheres are designed to offer greater ranges of motion and theoretically may reduce the risk of impingement and notching. The purpose of this biomechanical study is to demonstrate the difference in range of motions with each design of glenosphere. To our knowledge there is no published literature evaluating this design differences.

The SMR (Lima Orthotec) reverse total shoulder prothesis was implanted into a synthetic bone model (Sawbones, Pacific Laboratories, Vashon, Washington). Four different types of glenospheres (Standard 36 mm, Eccentric 36 mm, Standard 44 mm, Eccentric 44 mm) were then implanted into the same model which was fixed on a measurement table. The precision coordinate measurement device (FARO-Arm, SO6/Rev22, FARO Technologies Inc., Lake Mary, Florida) was used to establish the centres of rotation and ranges of motion.

To date, the collection of data has just been completed, but the data are yet to be analysed. In conclusion, this is a biomechanical study evaluating the ranges of motion and risk of notching, comparing different designs of glenospheres in Reverse Total Shoulder Joint Replacement.

Total elbow arthroplasty (TEA), as a primary procedure and open reduction and internal fixation (ORIF) have been used to treat complex intra-articular distal humeral fractures in elderly patients. The failure rate after ORIF is high and TEA has often been used as a salvage procedure. Although satisfactory results have been reported after TEA as a primary procedure, there are no publications reporting the results of TEA after failed internal fixation (FIF). In this study we compared the results of patients that had TEA after FIF with those that had had primary arthroplasty (PA). We reviewed the results of 9 consecutive patients who had FIF with 12 patients who had PA. All the operations were performed by one surgeon using the same technique and same prosthesis. Both groups of patients were similar with respect to ages, sex, co-morbidity and hand dominance. The mean follow-up for both groups of patients was 5 years. At final review, patients who had had FIF had a mean Mayo score of 68 and a range of flexion/extension of 90 degrees, there was 1 infection and 1 case of loosening. The PA group had a mean Mayo score of 88 and a range of flexion/extension of 96 degrees, there were no cases of infection or loosening. This study shows the results of TEA are satisfactory either as a PA or after FIF, however the results after PA are significantly better than after FIF.

Implant malposition remains one of the common causes of total knee replacement (TKR) failure and increased wear. Recent advances in computer technology have made available navigation systems for TKR and other orthopaedic procedures. The purpose of our study was:

to develop a method to assess the accuracy of an image-free TKR navigation system;

The system chosen was an image-free system based on electromagnetic technology, the MedTronic AxiEM TKR navigation system. To facilitate measurements, an artificial leg (phantom) was constructed from machined Plexiglas with simulated hip and knee joints. Additional joints located at the midshaft of the tibia and femur allowed deformation in the flexion/extension (y), varus/valgus (x) and rotational (z) planes. Using a highly accurate digital calliper unit (FaroARM Technologies, USA) to precisely measure co-ordinates with pre-machined points on the phantom, a software program was developed to convert these local co-ordinates into a determination of actual leg alignment. This technique was verified using repeated measurement with variable coordinates, giving accuracy to within 0.05 of a degree.

Simulated procedures were then performed with both normal and abnormal leg mechanical axis. At specific points in the procedure, information was compared between the FaroARM digital measurements and the CAS system. Repeated serial measurements were undertaken. In the setting of normal alignment, accuracy to within one degree was demonstrated. In the setting of abnormal x, y and z plane alignment in both femur and tibia, accuracy to within two degrees was demonstrated.

Several clinical studies have been performed to assess the precision of computer navigation in TKR. This study was designed to assess the accuracy of a clinically validated navigation system. The study demonstrates the high level of in-vitro accuracy of the MedTronic AxiEM navigation system in both normal and abnormal mechanical leg alignment settings.

This study evaluated the impact of smoking on the surgical outcome of rotator cuff repair controlling for age, gender, and size of tear.

Two hundred and fifty patients were evaluated by a blind evaluator and by self report (SST and WORC questionnaires) at baseline and one year post-op. Types of cuff repair included arthroscopic, mini-open and open procedures. Smoking status was evaluated as a current smoker, quit, or never smoked. Smoking history was subsequently dichotomised into smoker and non-smoker. Generalised linear modeling was used to determine the impact of smoking on surgical outcome using age, gender, and tear size as covariates.

The mean age of the population used was 56+/−11 years in which 70% were males and 30% females. Tear size was distributed amongst this population as small (0–1 cm {44.9%}), moderate (1–3cm {22.7%}), large (3–5cm {15.2%}) and massive (5+cm {17.2%}). All preliminary analyses indicated gender affected tear size and surgical outcomes, and was also associated with smoking status. Due to this confounding effect, males and females were separated for subsequent analysis. The SST questionnaire found smoking to have a significant negative effect on the 1-year l outcomes of males (8.5 vs. 6.1 p=0.025). A similar trend was seen with the WORC (p=0.07). No significant effects were seen for females, but the sample size was underpowered.

Analysis of this population of rotator cuff repairs showed complex interrelationships may exist between gender, age, physical demands and smoking status. The existence of these confounding interrelationships may explain the mixed results seen in the literature concerning smoking and orthopedic procedures. This relatively large cohort established a negative impact of smoking on outcome, after controlling for covariates and confounders. Future research on mediators of cuff outcome should consider potential confounders. Conclusion: Smoking negatively effected surgical outcomes for males but was inconclusive for females. Sex behaved as a confounding variable that masked the smoking effects.

A number of densitometry studies have reported dramatic density losses in the acetabular region after uncemented Total Hip Arthroplasty (THA)1,2. However the mechanical implication of such loss is not yet known. This study aims to perform a mechanical analysis with patient specific Finite Element (FE) models to find out how the stress distribution affects the Bone Mineral Density (BMD) changes after uncemented THA.

An existing patient CT dataset collected for a densitometry study was used to generate patient-specific FE models with a previously validated FE mesh generation method3. Boundary and loading conditions included the hip joint force and the forces of 21 muscles attached to the pelvic bone at eight characteristic phases of a gait cycle 4. Tensile and compressive components of principal stresses were calculated after each simulation.

In general, both compressive and tensile principal stresses decreased after uncemented THA but the magnitude of decrease for tensile stresses was much greater than compressive stresses. The changes in tensile stresses were matched with BMD loss patterns. In particular, the densitometry study revealed that areas dorsal to the prosthesis lost more bone density than areas ventral to the prosthesis1. The stress distribution pattern showed that such areas experienced high tensile stress initially and then a dramatic decrease in their magnitude while their compressive stresses remained relatively unchanged. On the other hand, the regions where BMD was maintained - the areas superior to the cup - experienced high compressive stresses initially, which remained relatively high three years after the surgery.

Although it is a result from one patient, results suggest that changes to tensile and compressive stresses might influence BMD differently after uncemented THA. Our hypothesis is that regions with high tensile stress experience bone loss while BMD of the regions with high compressive stress are maintained. More patient datasets are being processed to test this hypothesis. Findings from this study can explain the phenomena of retroacetabular osteolysis, late migration and implant failure of press-fit cups observed in long-term clinical studies.

Implant malposition is one of the most common causes of failure in resurfacing arthroplasty of the hip (RAH). Recent advances in computer technology have made available navigation systems for RAH and other orthopaedic procedures. The purpose of our study was:

to develop a method to assess the accuracy of an image-free RAH navigation system;

We used the Ci-CAS RAH navigation system (DePuy - BrainLab). To facilitate measurements, an artificial leg (phantom) was constructed from machined aluminium with simulated hip and knee joints. The hip and knee articulating surfaces were synthetic bone material (Sawbones – Pacific Laboratories). An additional joint located at the trochanteric region allowed deformation in varus/valgus and ante/retroversion of the head/neck segment. Using a highly accurate digital calliper unit (FaroARM Technologies, USA) to precisely measure co-ordinates with pre-machined points on the phantom, a software program was developed to convert these local co-ordinates into a determination of actual anatomy and leg alignment. This technique was verified using repeated measurement with variable co-ordinates, giving accuracy to within 0.05 of a degree.

Simulated procedures were performed with both normal and abnormal anatomy of the proximal femur. At specific points in the procedure, information was compared between the FaroARM digital measurements and the Ci-CAS system. Repeated serial measurements were undertaken. In the setting of normal alignment, accuracy to within 0.5 degrees was demonstrated. In the setting of abnormal alignment (varus/valgus and ante/retroversion) of the proximal femur, accuracy to within 2 degrees was demonstrated.

To our knowledge, this is the first study to assess accuracy of a RAH navigation system. The study demonstrates a satisfactory level of accuracy for the Ci-CAS in both normal and abnormal anatomical settings. Currently, no international standard or methodology exists against which these results can be compared. In the near future, introduction of new navigation technologies will make crucial the development of international standards for pre-clinical validation of computer-assisted navigation systems. The present study is a first attempt to address this issue.

Background: Calcaneonavicular coalitions (CNC) have been reported to be associated with anatomical aberrations of either the calcaneus and/or navicular bones. These morphological abnormalities may complicate accurate surgical resection. Three-dimensional analysis of spatial orientation and morphological characteristics may help in preoperative planning of resection.

Materials and Methods: Sixteen feet diagnosed with CNC were evaluated by means of 3D CT modeling. Three angles were defined that were expressed in relation to one reproducible landmark (lateral border of the calcaneus): the dorsoplantar inclination, anteroposterior inclination and socket angle. The contact surface area was determined from the depth and width of the coalitions. Three-dimensional reconstructions of the calcanei evaluated the presence and morphology of the anterior calcaneal facet and of a navicular beak. The inter-observer correlations were assessed for the accuracy of the measurement methods. Sixteen normal feet were used as controls for comparison of the socket angle and anatomy of the anterior calcaneal facet and of the navicular beak.

Results: The dorsoplantar inclination angle averaged 50° (±17), the anteroposterior inclination angle 64° (±15), and the pathologic socket angle 98° (±11). The average contact area was 156mm2. Ninety-four percent of all patients in the CNC group revealed a plantar navicular beak. In 50% of those patients the anterior calcaneal facet was replaced by the navicular portion and in 44% the facet was totally missing. In contrast, the socket angle in the control group averaged 77° (± 18), which was found to be statistically different than the CNC group (p=0.0004). Only 25% of the patients in the control group had a plantar navicular beak. Statistically significant inter-observer correlations were found for all measured angles.

Conclusions: Computer aided CT analysis and reconstructions help to determine the spatial orientations of CNC and provide useful information in order to anticipate morphological abnormalities of the calcaneus and navicular.

Cannulated screw fixation is currently the treatment of choice for slipped capital femoral epiphyses (SCFE). A SCFE module of the Bonedoc simulator was created in order to test the ability of advanced trainees to place the screw in the correct position, and the practicality of using the simulator within the orthopaedic surgery training curriculum.

Bonedoc (University of Auckland) is a virtual reality simulator of image guided orthopaedic operations1. This simulator runs in Internet Explorer (Microsoft, USA) using the Octaga (Octaga, Norway) plugin. The total download is around 4 MB. The SCFE module was created from a CT scan of a Grade 2 acute on chronic SCFE. DICOM images were imported into 3DView (www.rmrsystems.co.uk) and a mesh created. The generic femur from the DHS module was morphed within the CAD package Blender (Blender.org) to conform to this reconstructed SCFE mesh.

Forty two advanced trainees operated on the same virtual SCFE during a training weekend. The trainees had 25 minutes to become familiar with the simulator and complete the operative case. The trainees performed all tasks relevant to the operation. At the operation’s conclusion the trainees self-assessed their performance. Subsequently the simulator provided surgically relevant objective feedback on aspects such as exact position of the screw, misplaced attempts and the number of x-rays. The results were analysed using SAS (SAS Institute, USA) in subgroups based on year on the scheme, as well as correlated within each operation.

There was no difference in the accuracy with which the virtual slipped capital femoral epiphysis was pinned by trainees in different years in the training programme. However, 26 of the 39 of the virtual screws were placed in the superior direction. There was no correlation between number of X-ray images taken and final accuracy of screw placement. The number of misplaced drill holes was correlated both with number of X-ray images taken (p< 0.01) and operative time (p< 0.01) but not with final accuracy of the screw. An increase in misplaced attempts was correlated with angulation errors in the anterior plane (p< 0.01). There was no correlation between the trainees’ self assessment and any of the measured variables.

The Bonedoc simulator provides a means to test trainees on technical aspects of a surgical procedure. It provides objective results, which can mimic real world outcomes. In addition, the ability to test all trainees on the same virtual operative case allows standardisation of assessment. All trainees completed the task to a similar level of accuracy, which may reflect the overall skill level in advanced trainees within the New Zealand. However, many trainees placed the screw in the superior portion of the femoral head, which is thought to increase the risk of avascular necrosis2. Further work is required to evaluate how accurately performance on the simulator predicts performance in the operating theatre

Cerebral palsy (CP) results from an injury to the immature brain; and it leads to progressive musculoskeletal (MS) impairment in most affected patients. Orthopaedic surgery involving muscle-tendon lengthening is a method for managing short muscles in CP patients. Knowledge of muscle length prior to surgery is beneficial to surgical success. However, using common assessment methods like 3D gait analysis or physical examination, accurate pre-surgery estimation of muscle lengths during walking is difficult.

Computer models of the lower limbs, which provide more insight into muscle functioning during walking, have become increasingly important within the research field of CP. MS models are commonly driven by joint kinematics from clinical gait analysis. The most often used MS model in CP related research is based on the geometry of an adult human man with muscles modelled as line segments. This approach might be reasonable for small muscles with well-defined paths; however, for long muscles with multiple attachment points and curved paths, a more realistic 3D muscle model is required.

The aim of this study is the development of a clinical assessment tool for CP patients by incorporating kinematic data from gait analysis into a 3D finite-element MS model of the lower limbs. Ethical approval has been obtained to develop subject-specific MS models of 12 children with CP and 12 control children (age 8 – 12 years) based on magnetic resonance images. Kinematic data from 3D gait analysis is used as input data to transform the bony structures. Soft-tissue muscle deformation is modelled according to a variant of free-form deformation called the Host-Mesh Fitting Technique. So far, MS models of the lower limbs of three control children and of one child with CP were developed. The resulting muscle length changes during walking agree reasonably well with published data. The proposed modelling approach together with the library of 24 MS models will enable us to develop a powerful tool to investigate gait of children with CP.

The goal of this study was to determine which of two techniques for the treatment of peri-prosthetic femoral shaft fractures has the greatest torsional integrity. The study designed was a laboratory study, using 13 matched pairs of embalmed femurs. The femurs were implanted with a cemented total hip prosthesis, with a transverse osteotomy distal to the stem. These fractures were fixed either with a metal plate with three proximal unicortical screws and three distal bicortical screws or with three proximal cables and three distal bicortical screws. The fracture fixation was tested to failure in torsion. The pattern of failure and torsional limits were recorded.

There was no significant difference to failure level between the two constructs. Failure with the proximal unicortical screws was usually catastrophic versus non-catastrophic with proximal cables. The femurs were significantly more likely to fracture in internal rotation.

Treatment with proximal cables has the same load to failure in torsion but significantly less complications than with unicortical screws, in agreement with the literature. The findings of the construct being weaker in internal rotation, appears to be a new finding and an area of possible new research.

The purpose of this study was to establish a model to predict the future need for total hip and knee replacement surgery over the next ten years.

Analysis based on queuing theory and Ontario data (Ontario Joint Replacement Registry) considered such factors as changing demographics, specific wait time objectives and changing indicators to predict the future need for THR and TKR up to 2015.

26 725 Ontarians were waiting for THR and TKR surgery on any given day in 2004–05. Each month, the number of new decisions for surgery exceeded the actual number of surgeries by over 20%, adding another five hundred patients to the wait list. We predict that the population > fifty-five years of age will increase by 3.4% annually and that the willingness of patients to consider TJR surgery will increase by 8.7%/year To reduce wait times and establish a steady state of waiting (less than 6 months wait), more than 50 000 surgeries per year must be provided within five years and 70 000 total joint replacements per year by 2014–15 as compared to the 31 448 performed annually at this time. Providing this volume of surgeries means that the number of surgeons will have to double within five to seven years.

The results of this queuing theory analysis predict a substantial need for markedly increased THR and TKR volumes and orthopaedic manpower over the next decade.

Long term clinical follow-up of total hip arthroplasty (THA) has identified problems associated with cyst formation. Such cysts are formed as a result of expansile osteolysis, which starts on a small area of the skeleton and spreads into the bone away from the surface of the prosthesis. Since large areas of the prosthesis are still in immediate contact with the skeleton the prosthesis is not loose and the patients are usually without pain. However this form of osteolysis may destroy large areas of the skeleton before it is detected and result in a sudden fracture due to a weakened skeleton. While there are some short term prospective trials that have shown changes in bone density in the periacetabular region, one needs a biomechanical model to understand factors that influence bone remodeling leading to cyst formation. This study aims to develop a mathematical model for studying the mechanical effects of bone cysts in the acetabulum of THA patients.

2D finite element (FE) models of patients with known restroacetabular cystic disease were generated using coronal CT images from the central region of the acetabulum. The boundary between bone and soft tissue was segmented and an FE model generated. Mesh convergence tests were performed to identify a suitable level of mesh refinement. Three material zones representing– cortical bone (E=17GPa), cancellous bone (E=1GPa) and a titanium cup (E=120GPa) – were included in the model. A series of simulations were run to investigate how cysts affect stress distribution as well as the mechanical consequence of medial wall deficiency.

The presence of a cyst did not alter the pattern of stress distribution in the lateral and medial wall. But the strain energy function increased significantly at the inferior margin of the cyst within its cancellous bone. This may encourage bone formation at the cyst margin and help to explain the sclerotic walls seen in some cysts. Models with absent medial walls showed that both compressive and tensile stresses lowered in the cortical wall and the strain energy function reduced almost to zero. This suggests that a medial wall defect has a high risk of progression.

The current 2D model cannot incorporate complex acetabular geometry or complex forces acting on the hip. Therefore the current model will be further developed into a 3D FE model of the whole pelvis that also represents the pelvic ring structure more adequately. Physiologically meaningful boundary conditions as well as patient specific geometry and material properties will be used to investigate mechanical effects of bone cysts realistically.

Lateralisation of the tuberosity tibia causes distal malalignment of the extensor mechanism of the knee and can lead to lateral tracking patella (LTP), resulting in anterior knee pain, or objective patellar instability (OPI), resulting in recurrent luxations. For a precise preoperative diagnosis the tuberositas tibia (TT) trochlear groove (TG) distance was measured on a CT scan. A distance of more than 15 mm was considered to be pathological.

In a prospective study, the clinical results of a subtle, CT-guided medial tuberosity transfer for LTP and OPI were evaluated. 30 Consecutive patients with LTP and 30 patients with OPI and an increased TT TG were included. Outcomes were documented at 3, 12 and 24 months follow-up using the Lysholm scale, the Kujala score, and a visual analogue pain score. Postoperatively all but one patient reported good improvement in stability (no persistent subluxations or luxations). All patients had a marked improvement in pain and functional scores at follow up. Complications seem to be related to the peroperative technique. CT-guided TT transfer appears to be satisfactory and safe method for treating patients with an increased TT TG leading to either LTP or OPI.

Introduction: This study examined the cohort of patients selectively screened over a 5 year period with ultrasonography according to our risk factors (positive Ortolani or Barlow manoeuvre, breech presentation, first degree affected relative and talipes equinovarus) for developmental hip dysplasia (DDH). The aims were to evaluate the success of those managed in a Pavlik harness and identify predictive factors for those that failed treatment.

Methods: 1181 patients were selectively screened between 1999 and 2004. Of those, 128 patients (189 hips) were identified as having hip instability. Failure was defined as inability to achieve or maintain hip reduction in a Pavlik harness. A proforma was designed to document patients’ risk factors and ultrasound findings at time of initial dynamic ultrasound scan where the senior radiographer and treating consultant were present. Each hip was classified according to Graf type. Acetabular indices were recorded prior to discharge.

Results: All 128 patients with hip instability were managed in a Pavlik harness. This was abandoned for surgical treatment in 9 patients (10 hips) giving a failure rate of 5.3 % (0.17 per 1000 live births). All those successfully managed had an acetabular index of less than 30 degrees at follow up (6 – 48 months). 7 hips in the series were classified as Graf type IV, of these, 6 went on to fail management in a Pavlik harness. 67% of those that failed were also breech presentation compared to 22% of those managed successfully. There were no complications associated with management in a Pavlik harness. 16 patients born within our region presented after 12 weeks of age with DDH resulting in a late presentation rate of 0.3 per 1000 live births.

Discussion: Our overall rate of selective screening is 14 per 1000 live births with a subsequent treatment rate of 2.3 per 1000 is comparable with other centres. Our rate of failure for DDH in a Pavlik harness 0.17 per 1000 live births is an improvement on any previously published results. Irreducible hips, Graf type IV hips and breech presentation correlated with a high likelihood of treatment failure.

This article has been retracted, an editorial will follow.

Introduction: Epidemiology suggests that an intrauterine nutrient restriction increases the likelihood of osteoporosis in later life, possibly due to differences in bone structure and strength. We hypothesise that, in an ovine model, early nutritional compromise reduces vertebral cancellous bone density and cortical thickness, and thereby reduces vertebral compressive strength.

Materials and methods: Lumbar spines were dissected from 8 sheep (6 male, 2 female: mean age 2.7 yrs). Spines were divided into different groups, based on the early diet of the sheep: group CC received a control diet, group IU received low protein in utero, and group PN received low protein both in utero and postnatally. Fifteen motion segments (consisting of two vertebrae and the intervening disc and ligaments) were prepared from the spines, and compressed to failure using a hydraulically-controlled materials testing machine to obtain yield strength. 1mm-thick bone slices were taken from the mid-sagittal and para-sagittal regions of each vertebral body and micro-radiographed. Digital images of the micro-radiographs were analysed to obtain the cancellous bone density in anterior and posterior regions, and the cortical thickness in the anterior, posterior, superior and inferior regions. Repeated measures ANOVA was used to test for differences in parameters at the different locations, and between the groups.

Results: The anterior cortex was 28% thinner for the IU group, and 23% thinner for the PN group compared to controls (both p< 0.001). In the PN group, the superior cortex was also 18% thinner than controls (p< 0.02). There was no significant difference between cancellous bone density in either region. Yield strength was 16% lower in the IU group compared to controls, but this did not reach significance.

Discussion: In the nutritionally compromised groups, cortical thickness was lower in regions of the vertebral body where fractures often occur in elderly people. However, the reduction in cortical thickness is not accompanied by a significant reduction in compressive strength in the sheep model. These findings suggest that the well-maintained cancellous bone protects the vertebra from fracture.

In recent years, some attempts have been made to develop a method that generates finite element (FE) models of the femur and pelvis using CT. However, due to the complex bone geometry, most of these methods require an excessive amount of CT radiation dosage. Here we describe a method for generating accurate patient-specific FE models of the total hip using a small number of CT scans in order to reduce radiation exposure.

A previously reported method for autogenerating patient-specific FE models of the femur was extended to include the pelvis. CT osteodensitometry was performed on 3 patients who had hip replacement surgery and patient-specific FE models of the total hip were generated. The pelvis was generated with a new technique that incorporated a mesh morphing method called ‘host mesh fitting’. It used an existing generic mesh and then morphed it to reflect the patient specific geometry. This can be used to morph the whole pelvis, but our patient dataset was limited to the acetabulum. An algorithm was developed that automated all the procedures involved in the fitting process.

Average error between the fitted mesh and patient specific data sets for the femur was less than 1mm. The error for the pelvis was about 2.5mm. This was when a total 18 CT scans with 10mm gap were used – 12 of the femur, and 6 of the pelvis. There was no element distortion and a smooth element surface was achieved.

Previously, we reported a new method for automatically generating a FE model of the femur with as few CT scans as possible. Here we describe a technique that customizes a generic pelvis mesh to patient-specific data sets. Thus we have developed a novel hybrid technique which can generate an accurate FE model of the total hip using significantly less CT scans.

An automated method of generating FE models for the total hip with reduced CT radiation exposure will be a valuable clinical tool for surgeons.

In recent years, some attempts have been made to develop a method that generates finite element (FE) models of the femur and pelvis using CT. However, due to the complex bone geometry, most of these methods require an excessive amount of CT radiation dosage. Here we describe a method for generating accurate patient-specific FE models of the total hip using a small number of CT scans in order to reduce radiation exposure.

A previously reported method for autogenerating patient-specific FE models of the femur was extended to include the pelvis. CT osteodensitometry was performed on 3 patients who had hip replacement surgery and patient-specific FE models of the total hip were generated. The pelvis was generated with a new technique that incorporated a mesh morphing method called ‘host mesh fitting’. It used an existing generic mesh and then morphed it to reflect the patient specific geometry. This can be used to morph the whole pelvis, but our patient dataset was limited to the acetabulum. An algorithm was developed that automated all the procedures involved in the fitting process.

Average error between the fitted mesh and patient specific data sets for the femur was less than 1mm. The error for the pelvis was about 2.5mm. This was when a total 18 CT scans with 10mm gap were used – 12 of the femur, and 6 of the pelvis. There was no element distortion and a smooth element surface was achieved.

Previously, we reported a new method for automatically generating a FE model of the femur with as few CT scans as possible. Here we describe a technique that customizes a generic pelvis mesh to patient-specific data sets. Thus we have developed a novel hybrid technique which can generate an accurate FE model of the total hip using significantly less CT scans.

The correct positioning of implant components in total knee replacement (TKR) is important for a successful long-term outcome. In order to address the problems inherent with conventional alignment methods, several computer-assisted navigation systems (CAS) have been developed. Despite numerous reports of clinical outcomes and system reliability, there is a lack of studies independently evaluating the precision and accuracy of such systems. We report on the design and development of a method and device to evaluate the accuracy of such a computer-assisted navigation system in two situations; 1) Normal or near-normal lower limb mechanical axis, and 2)Simulated femoral and/or tibial extra-articular deformity in either varus/valgus (x), internal/external rotation (y) or flexion/extension (z) planes.

The system assessed was the Ci Knee-CAS navigation system (BrainLab/De Puy). This image-free system requires the registration of specific anatomical points to identify the mechanical axis of the lower limb and therefore provide information on resection level and alignment. In order to precisely measure and accurately reproduce these points we constructed a phantom device along anatomical guidelines, with lockable joints located at the mid-shaft of both femur and tibia. We then identified geometric CAS data; 1) Tibial resection height, and 2) Tibial resection plane, and using specially written software compared this against validated co-ordinate measurements independently obtained by a FaroArm co-ordinate measurement system (FARO Technologies, USA). This enabled data from the navigation system to be directly compared against highly accurate reference measurements.

Accuracy of the system was then assessed with both normal mechanical alignment of the lower limbs and simulated extra-articular deformity.

An abnormal lateral position of the tibial tuberosity causes distal malalignment of the extensor mechanism of the knee and can lead to lateral tracking of the patella causing anterior knee pain or objective patellar instability, characterised by recurrent dislocation. Computer tomography is used for a precise pre-operative assessment of the tibial tubercle-trochlear groove distance. A distance of more than 15 mm is considered to be pathological and an indication for surgery in symptomatic patients.

In a prospective study we performed a subtle transfer of the tibial tuberosity according to the information gained from the pre-operative CT scan. This method was applied to two groups of patients, those with painful lateral tracking of the patella, and those with objective patellar instability. We evaluated the clinical results in 30 patients in each group. The outcome was documented at 3, 12 and 24 months using the Lysholm scale, the Kujala score, and a visual analogue pain score.

Post-operatively, all but one patient in the instability group who had a patellar dislocation requiring further surgery reported good improvement with no further subluxation or dislocation. All patients in both groups had a marked improvement in pain and functional score. Two patients sustained a tibial fracture six and seven weeks after surgery. One patient suffered a per-operative fracture of the tibial tubercle which later required further fixation.

If carefully performed, this type of transfer of the tibial tubercle appears to be a satisfactory technique for the treatment of patients with an increased tibial tubercle-trochlear groove distance and who present with symptoms related to lateral maltracking of the patella.

Traumatic atlanto-occipital dislocation in adults is usually fatal and survival without neurological deficit is rare. The surgical management of those who do survive is difficult and controversial. Most authorities recommend posterior occipitoaxial fusion, but this compromises cervical rotation. We describe a case in which a patient with a traumatic atlanto-occipital disruption but no neurological deficit was treated by atlanto-occipital fusion using a new technique consisting of cancellous bone autografting supported by an occipital plate linked by rods to lateral mass screws in the atlas. The technique is described in detail. At one year the neck was stable, radiological fusion had been achieved, and atlantoaxial rotation preserved.

The rationale behind this approach is discussed and the relevant literature reviewed. We recommend the technique for injuries of this type.

Introduction: Fibroblast growth factor receptor 3 (FGFR3) is a tyrosine kinase membrane-spanning protein whose function is to regulate chondrocyte proliferation, differentiation and matrix production during cartilage development. Several mutations in FGFR3 have now been documented to link to human diseases. A number of these mutations result in constitutive activation of the FGFR3, leading to proliferation and premature differentiation of chondrocytes. Depending on the mutation and the resultant level of FGFR3 activation, mild to severe skeletal dysplasias such as achondroplasia (ACH), hypochondroplasia (HCH), thanatophoric dysplasia type I (TDI) and type II (TDII), and severe achondroplasia with developmental delay and acanthosis nigrans (SADDAN) may result. It has been postulated that the signalling pathways downstream of FGFR3 may be responsible for activating transcription factors, leading to up-regulation of cell cycle inhibitors and causing abnormal suppression of chondrocyte cell proliferation. However, the precise signalling pathways involved in FGFR3 mutation have as yet to be elucidated. The aim of this study was to investigate and compare the differences in the downstream signalling pathways between FGFR3 mutants.

Methods and Results: Wild type FGFR3 has been cloned into expression vector pcDNA3 and the construct has been used to generate four different FGFR3 mutants using site-directed mutagenesis. The mutations which have been introduced and the types of dysplasia they correspond to were as follows: K380R (ACH), N540K (HCH) and K650E (TDII). A kinase dead form of the receptor, K504R has also been generated. Wild type and each of the four mutant FGFR3 proteins in pcDNA3 vector have been successfully transfected into 293T cells using the calcium phosphate method. Immunoprecipitation and Western Blot analysis of cell lysates revealed expression of wild type protein in three isoforms of size 135kDa (mature), 120kDa (intermediate) and 98kDa (immature). The mutant proteins all followed a similar pattern of expression with the exception of the TDII mutant that did not express the mature form of the FGFR3. Changes in MAPK, PLCã and STAT 1 signalling pathways in response to FGFs-1, 2, 9 and 18 in the 293-cells of wild type and mutant forms of FGFR3 are now under investigation, in an attempt to define which pathways are mostly responsible for the resultant abnormal phenotypes.

Discussion: Genomics studies have demonstrated that FGFR3 expression is significantly upregulated during the osteoblastic differentiation of mesenchymal stem cells (MSCs) under BMP-2 stimulation in vitro. Subsequent functional studies have demonstrated that a selective ligand for FGFR3, FGF9, is able to induce tyrosine kinase signalling, and the osteoblastic differentiation of MSCs in vitro. Further understanding the signalling mechanisms of FGFR3 activation in normal and mutant forms may lead to discover potential anabolic agents that are based on FGFR3-FGFs pathways.

There is increasing pressure to develop virtual reality surgical simulation that can be used in surgical training. However, little is known of the attitudes of the surgical community towards such simulation, and which aspects of simulation are most important.

A postal survey on attitudes to surgical simulation was sent to all New Zealand orthopaedic surgeons and advanced trainees. This comprised 44 questions in ten sections, using either a visual analogue scale (0 to 10) or free text box replies. Results were analysed for two sub-groups; surgeons qualified before 1990 and those qualified in or after 1990 or still in training.

Of 208 possible responses, 142 were received, a response rate of 68%. Only 4 respondents had tried a surgical based simulator. Earlier qualified surgeons were more likely to agree that simulation was an effective way to practice surgical procedures, median score 7.7 versus 5.6 (p=0.03). Both groups thought the most important task for simulation was practicing angulation/spatial orientation (median score 8.4/10), while a realistic view of the operation was the most important requirement (median score 9/10). Both groups were unconvinced that simulation would impact on their practice in the next five years, with this statement being scored lower by later qualified surgeons, median score 2.4 versus 4.1 (p=0.04).

Orthopaedic surgeons in New Zealand are supportive of surgical simulation but do not expect simulation to have an impact in the near future. Intriguingly, later qualified surgeons and trainees are more sceptical than their earlier qualified colleagues.

Introduction: This study examined the cohort of patients selectively screened over a 5 year period with ultrasonography according to our risk factors (positive Ortolani or Barlow manoeuvre, breech presentation, first degree affected relative and talipes equinovarus) for developmental hip dysplasia (DDH). The aims were to evaluate the success of those managed in a Pavlik harness and identify predictive factors for those that failed treatment.

Methods: 728 patients were selectively screened between 1999 and 2004. Of those, 128 patients (189 hips) were identified as having hip instability. Failure was defined as inability to achieve or maintain hip reduction in a Pavlik harness. A proforma was designed to document patients’ risk factors and ultrasound findings at time of initial dynamic ultrasound scan where the senior radiographer and treating consultant were present. Each hip was classified according to Graf type. Acetabular indices were recorded prior to discharge.

Results: All 128 patients with hip instability were managed in a Pavlik harness. This was abandoned for surgical treatment in 9 patients (10 hips) giving a failure rate of 5.3 %. All those successfully managed had an acetabular index of less than 30 degrees at follow up (6 – 48 months). 7 hips in the series were classified as Graf type IV, of these, 6 went on to fail management in a Pavlik harness. 67% of those that failed were also breech presentation compared to 22% of those managed successfully. There were no complications associated with management in a Pavlik harness.

Discussion: Our overall rate of selective screening is 14 per 1,000 with a subsequent treatment rate of 2.3 per 1,000, which is comparable with other centres. Our rate of failure for DDH in a Pavlik harness (5.3 %) is extremely encouraging. Graf type IV hips and breech presentation correlated with a high likelihood of treatment failure.

Aim: Assessing Polyethylene wear is very important in following up patients after Total hip replacement (THR) and Livermore method (using callipers) is routinely used by clinicians in calculating this wear. Our aim was to assess if ‘Imagika’, a new computer software programme can accurately assess polyethylene wear(PE-wear). We also compared the computer software with the Livermore method in calculating wear.

Method: We used 15 different THR X rays of patients who had an ABG total hip replacement done. X rays that were included for the calculations were taken at different time intervals following the operation. Wear was calculated on each X ray by 3 clinicians using both the methods, on 3 separate occasions. We compared the Livermore method and the computer software for consistency of measurements and also calculated the inter and intra observer variability for both.

Results: There was a statistically significant difference (at the 5% level) between the measurements taken by the Imagika software and the Livermore method. F(1,88) = 5.38, p< 0.05. There was a statistically significant difference in the inter-observer measurements using the Livermore method. F(2,42) = 4.18, p< 0.05, but there was no significant inter-observer variation using the Imagika computer software. There was no statistically significant difference (at the 5%level) in the intra-observer variability of both groups.

Conclusion: The Imagika computer software proved to be better than the Livermore method in calculating wear with regards to inter-observer bias. There was also a significant difference between measurements taken using both methods. We conclude that the computer software may be a more accurate tool in the assessment of PE-wear in the future.

The object of this study was to develop a method to assess the accuracy of an image-free total knee replacement navigation system in legs with normal or abnormal mechanical axes. A phantom leg was constructed with simulated hip and knee joints and provided a means to locate the centre of the ankle joint. Additional joints located at the midshaft of the tibia and femur allowed deformation in the flexion/extension, varus/valgus and rotational planes. Using a digital caliper unit to measure the coordinates precisely, a software program was developed to convert these local coordinates into a determination of actual leg alignment. At specific points in the procedure, information was compared between the digital caliper measurements and the image-free navigation system. Repeated serial measurements were undertaken. In the setting of normal alignment the mean error of the system was within 0.5°. In the setting of abnormal plane alignment in both the femur and the tibia, the error was within 1°. This is the first study designed to assess the accuracy of a clinically-validated navigation system. It demonstrates in vitro accuracy of the image-free navigation system in both normal and abnormal leg alignment settings.

Introduction: Patello-femoral complications are a major problem after total knee arthroplasty (TKA). Purpose of the present study was to analyze patello-femoral complications and function after two different posterior-stabilized TKA designs (Optetrak 913 vs IB-II).

Materials and Methods: This study was performed in two consecutive phases. In the first phase 1410 TKA’s performed by the senior author between 1994 and 1998 were considered for chart review. Within this period, the last 300 IB-II and the first 300 913 performed were analyzed for patello-femoral complication rate. In the second phase, of the 600 charts analyzed, two matched groups (50 patients each of IB-II and 913), were selected for a clinical (Knee Society score), functional (HSS Patellar score) and radiological assessment (AP, Lateral, Merchant, modified-wb Merchant views).

Results: A lateral retinacular release was performed in 30% for the IB-II and 16% for the 913 (p=0.02). The following patello-femoral complications were encountered (phase-1):

IB-II 913

Patellar clunk 3.5% 0.3%

Dislocation 0% 0.3%

Fracture 0% 0.3%

Loosening 0% 0%

Clinical results at follow-up (phase-2) did not show any significant difference between the two matched groups in terms of Knee and Function scores (p=0.7). Patellar score showed a higher rate of excellent and good results in the 913 group (88% vs 81%: p=.043). Anterior knee pain was only mild and activity related in 26% of the IB-II and 14% of the 913 (p=.025). In a multivariate regression analysis, radiographic patellar tilt, subluxation, and height, did not correlate with clinical outcomes, whilst bone-implant contact showed a trend towards a higher incidence of pain, particularly when associated with asymmetric patellar resection.

Discussion: At an intermediate follow-up, the Optetrak 913 prostheses showed fewer complications and an improved patello-femoral function compared to the IB-II prosthesis.

Introduction: Patello-femoral evaluation after total knee arthroplasty (TKA) is not addressed by most knee scoring systems. Patellar radiographic assessment after TKA is obtained with static, unloaded views that may not reproduce the in-vivo patello-femoral kinematics. The purpose of this study was to develop and validate new reliable and reproducible clinical and radiographic assessment tools for analysis of the patello-femoral joint in TKA.

Materials and Methods: The existing axial Merchant view was modified by positioning the standing patient in the semi-squatted position with the knees at 45°. Relationship between X-ray source, the angle of incidence on the joint, and the cassette position, were kept unchanged from the original view. The standing position and consequent muscle involvement were the only differences. The quality of the view was confirmed on a cadaveric knee model with multiple markers. Safety, reproducibility and clinical reliability were obtained in 100 posterior-stabilized TKA’s. These patients were assessed by a new Patella Scoring System (0–100 points). This system considers anterior knee pain, crepitus, stair performance and quadriceps strength. Radiographic abnormalities are calculated as deductions. Intra- and inter-observer variability were obtained comparing the results of two different investigators.

Results: The modified Merchant view showed significant patello-femoral tracking changes in 68% of patients. Twenty-one cases of bone-implant contact were observed when load was applied. Correlation between excellent-good clinical outcome and excellent patello-femoral performance was significantly higher for the Patellar Score compared to Knee Society Clinic or Function scores (p=.022, p=.014). Multivariate regression analysis of radiographic tilt, subluxation, and height, did not correlate with clinical outcomes, whilst bone-implant contact showed higher incidence of pain, particularly when associated with asymmetric patellar resection.

Conclusion: These new patello-femoral clinical and radiological assessment methods employed in the study represent additional valuable tools for the comprehensive evaluation of results in TKA.

Aim To assess whether prosthetic femoral stem centralisers have a detrimental effect on the maroporosity of the cement mantle, and if so, whether this is independent of their design and the rate of implantation.

Methods 30 identical moulded prosthetic femora were divided into 3 groups. Group 1; no centraliser (control), Group 2; centraliser A, Group 3 centraliser B. Using third generation cementation techniques and pressure monitoring, Charnley C-stems +/− the appropriate centraliser were implanted to a constant depth. Half in each group were implanted as rapidly as possible and the other half over 90 seconds. The stems were removed and the cement mantle then underwent a preliminary arthroscopic examination prior to being sectioned transversely at 3 constant levels. Each level was then photographed and digitally enlarged to a known scale to allow examination and determination of any cement voids (macropores) surface area.

Results There were no significant pressure fluctuations between the groups. Preliminary arthroscopic examination revealed that cement voids appeared more common when a centraliser was used. This difference was statistically confirmed (p=0.002) following sectioning of the specimens with cement voids found in 85% of femora when a centraliser was used and only 20% in the control group. Centraliser B performed worst with cement voids of a larger volume and more frequent occurrence (p=0.002). The macroporosity of the cement mantle was independent of the rate of implantation (p=0.39).

Conclusion The use of femoral stem centralisers is helpful in preventing malposition of the implant but results in increased macroporosity of the cement mantle. This may have implications regarding the longevity of an implant in terms of early loosening and therefore their design and use must always be carefully considered.

Introduction and Aims: CT is one of the most versatile and useful medical imaging modalities for computer assisted surgery (CAS) and monitoring bone remodelling. However, the high radiation dosage hinders its widespread use. We describe a method for generating smooth and accurate Finite Element (FE) meshes using CT data with reduced radiation exposure.

Method: We have performed serial CT assisted osteodensitometry measurement on seven patients who had a total hip replacement. FE models were generated automatically with cubic Hermite basis functions for both geometry and density. The meshes were fitted to the geometric and density data sets using least square’s fitting. Density was displayed over the surface of the elements using a colour spectrum. The effect of reducing radiation dosage was studied by generating five different types of FE meshes from each patient with different numbers of CT slices. The different mesh types were generated by varying the gap between slices.

Results: The mesh with the smallest number of CT slices used seven CT scans, with the gap between slices of 3cm on average while the mesh with the largest number of slices used 22 scans with the gap of 0.8cm. For the mesh with the largest number of CT slices, the average error after the geometric fitting was less than 0.5mm. The average error for the density fitting was 70.2 mg/ml. When expressed as the percentage to the overall density data range (0 ~ 1500 mg/ml), the average error was 4.7%. Meshes generated with a smaller number of CT slices had larger errors, and this increased as the number of slices used decreased. The error in geometry dropped dramatically (more than 50%) when more than 10 slices were used, whereas the error in density decreased approximately linearly as the number of slices increased. Overall, it was possible to generate realistic and smooth meshes with a geometrical error of less than 1.5mm and a density error less than 7% using 10 CT slices.

Conclusion: One strength of the current study is that we have used cubic Hermite elements, which requires much less information in generating FE meshes without sacrificing too much accuracy. Our study has shown that we can generate realistic and smooth meshes with about 10 CT slices of the proximal femur. This is important to enhance the power of CT in clinical applications.

We report the incidence and location of deep-vein thrombosis in 312 patients who had sustained high-energy, skeletal trauma. They were investigated using magnetic resonance venography and Duplex ultrasound.

Despite thromboprophylaxis, 36 (11.5%) developed venous thromboembolic disease with an incidence of 10% in those with non-pelvic trauma and 12.2% in the group with pelvic trauma. Of patients who developed deep-vein thrombosis, 13 of 27 in the pelvic group (48%) and only one of nine in the non-pelvic group (11%) had a definite pelvic deep-vein thrombosis. When compared with magnetic resonance venography, ultrasound had a false-negative rate of 77% in diagnosing pelvic deep-vein thrombosis. Its value in the pelvis was limited, although it was more accurate than magnetic resonance venography in diagnosing clots in the lower limbs. Additional screening may be needed to detect pelvic deep-vein thrombosis in patients with pelvic or acetabular fractures.

Aim: To identify the local and systemic morbidity of simultaneous sequential bilateral total knee arthroplasty in a large patient population and to undertake a comparative statistical analysis with a group of matched patients who underwent staged bilateral total knee replacement during the same period.

Methods: Theatre records at two regional district general hospitals were scrutinised to identify all patients who had undergone simultaneous sequential and staged bilateral total knee arthroplasty over a three year period. Patient case notes and hospital charts were retrospectively reviewed to obtain several outcome measures to allow subsequent risk factor assessment.

Results: 134 patients with 268 primary knee arthroplasties undergoing a simultaneous procedure were identified. The average age was 70 with a minimum follow up of 12 months. The study results revealed 1.5% mortality, 5.2% local complication and 14.9% systemic complication rates and this increased with age. During the same period 34 patients (68 knees) who had undergone staged procedures at least 3 months apart were also identified. Statistically significant findings between both groups included the reduced length of hospital stay, a 3-fold increase in the requirement for banked blood (particularly when either suction drainage or low molecular weight heparin thromboprophylaxis was used) and a higher degree of intra operative instability in those undergoing simultaneous bilateral total knee replacement.

Conclusions: Patients can continue to enjoy the benefits of simultaneous bilateral knee arthroplasty, however, extreme caution must be taken in selection of patients over 75 years, high dependency facilities must be available and an acceptable alternative to banked blood transfusion needs to be used.

Bone autograft contains living cells that participate in the healing process. Fragmentation and heat production during cutting will kill cells. We have investigated how excessive graft fragmentation and heating can be avoided.

Two prototype cutters were fabricated. Each had a single cutting edge at the front end of a 12 mm diameter collection barrel. The principal difference between the cutters was the rake angle (at the cutting edge): 23° on cutter #1 and 45° on cutter #2.

Thrust load, feed-rate, and torque were measured using an instrumented drill press. A total of 58 tests on specimens of fresh bovine cancellous bone (distal femur, ex-abattoir) and medium density polyurethane foam (Sawbones, WA. USA) (density 252 kg/m³) were conducted: twenty-four at 100 rpm and thirty-four at 200 rpm.

Small flake-like fragmented bone chips were encountered at low thrust loads. As thrust load was increased the chips became thicker. The average cutting energy for bone was 43.7 Nm (s.d. 48.2 Nm) for cutter 1 and 37 Nm (s.d. 27 Nm) for cutter 2. The average cutting energy for the foam was 13.9 Nm (s.d. 6.0 Nm) for cutter 1 and 8.1 Nm (s.d. 3.0 Nm) for cutter 2. Polyurethane results showed a similar trend.

A higher rake angle on a bone graft tool is associated with a lower cutting energy. In turn, a lower cutting energy will generate a lower temperature in the graft, a result that is beneficial for cell survival. Graft tool design can also influence bone chip size. These experimental results are being used for the development of cell-friendly tooling.

Periprosthetic bone density (BD) changes can be tracked using computed-tomography (CT) assisted osteodensitometry. Patient-specific computer-generated models allow for good visualisation of density changes in bone. We describe techniques for generating smooth and realistic finite element (FE) models that contain both BD and geometry from quantitative CT data using cubic Hermite elements.

FE models were created for three patients who had a total hip replacement. CT-scans were performed at 10 days, one year, and 3 years after the operation and calibrated using a synthetic hydroxyapatite phantom. FE models of the proximal femur were automatically generated from the CT data. Each model had on average 300 tri-cubic Hermite elements. Models were least squares fitted to the entire dataset. BD data was also sampled and fitted using the same cubic interpolation functions. Density was displayed using a colour spectrum.

Realistic patient-specific FE models were obtained. Density and changes in BD were easy to identify. The error in the geometric fitting (RMS distance between data points and the model surface) was generally less then 0.5 mm. The average error for the density fitting (RMS difference between each density data point and the interpolation function value at the same point) was 61.64 mg/ml or 3.08%.

CT osteodensitometry’s potential use as a clinical tool for monitoring changes to BD can be significantly enhanced when used in conjunction with realistic patient-specific finite element (FE) models. Realistic models can be generated with an economic use of scan data, thus keeping radiation dosage down.

Introduction: Previous in vivo kinematic studies have assessed total knee arthroplasty (TKA) motion under weight-bearing conditions. This in vivo study analyzed and compared posterior cruciate retaining (PCR) and posterior stabilized (PS) kinematics under passive and weight-bearing conditions in subjects implanted with both a PCR and PS TKA.

Methods: Eighteen subjects were implanted with a PCR and a PS TKA, by a single surgeon using a similar surgical technique. Both implant designs had similar condylar geometry. Femorotibial contact positions for all 18 subjects (PCR and PS), implanted by a single surgeon, were analyzed using video fluoroscopy. Each subject,while under fluoroscopic surveillance, performed a weight-bearing deep knee bend and a passive, nonweight-bearing flexion. Video images were downloaded to a workstation computer and analyzed at varying degrees of knee flexion. Femorotibial contact paths for the medial and lateral condyles, axial rotation and femoral condylar lift-off were then determined using a computer automated model-fitting technique. Femorotibial contact anterior to the tibial midline in the sagittal plane was denoted as positive and contact posterior was denoted as negative.

Results: Under passive and weight-bearing conditions, the PCR TKA experienced more paradoxical anterior translation than the PS TKA. Under passive, non weight-bearing conditions, the PS TKA, on average, experienced 3.5 mm of posterior femoral rollback, compared to only 0.6 mm for the PCR TKA. Under weight-bearing conditions, the PS TKA experienced only 0.6 mm of posterior femoral rollback, compared to 0.9 mm for the PCR TKA. The maximum anterior slide was 10.0 mm for the PCR TKA and only 2.7 mm for the PS TKA. There was greater variability in both the PCR and PS anteroposterior data. Subjects having a PCR TKA experienced more normal axial rotation patterns. Sixteen of 18 PCR TKA experienced a normal axial rotation pattern under weight-bearing conditions, while only 9/18 PS TKA experienced a normal pattern. Nonweight-bearing, passive axial rotation patterns were more abnormal for both groups than the weight-bearing patterns. The greatest difference between passive and weight-bearing conditions occurred in the condylar lift-off data. Under passive conditions, both TKA groups experienced significantly greater magnitude and incidence of condylar lift-off. The maximum amount of condylar lift-off under passive conditions was 5.0 mm for the PCR TKA and 6.4 mm for the PS TKA.

Discussion: This is the first in vivo kinematic study to assess a comparison between PCR and PS TKA implanted by the same surgeon in the same patient. Subjects in this study experienced more abnormal kinematic patterns, especially condylar lift-off, when tested under passive, nonweight-bearing conditions. Subjects having a PS TKA experienced less variability in their kinematic data, but PCR TKA, on average, experienced more normal axial rotation and less condylar lift-off.

Introduction Comminuted intra-articular fractures of the distal radius are severe injuries where the outcome depends on accurate anatomical reduction and reconstitution of the articular surface, and early mobilisation. This prospective outcome study aims to assess the anatomical and functional outcome of internal fixation of these complex fractures using a fragment specific fixation system.

Methods Fifty consecutive comminuted intra-articular distal radius fractures presenting at our hospital were treated by the one surgeon (MP). Inclusion criteria were age under 80 and AO classification C-3. Various combinations of wires, buttress pins/clips and plates were utilized according to each fracture configuration. No post-op splintage was used. All patients commenced hand therapy from day one post-op. Patients were reviewed at two weekly intervals till fracture union and monthly thereafter. All patients were independently assessed by a hand therapist for range of motion and grip strength. Patient function was assessed using the DASH (Disabilities of the Arm, Shoulder and Hand) and the PRWE scores. Thirteen males and 37 female with an average age of 53.8 (29 to 72) were treated with the TriMed between February 2002 and February 2003. Average follow-up was seven months (3 to 14).

Results All fractures had healed at the six week review, with mean palmar tilt of 12°, radial tilt of 19° and radioulnar variance of 5 mm, with articular step less than 1 mm. The mean DASH score was 19 (SD 9) and mean PRWE score was 19 (SD 11). Average range-of-motion was 65 (SD 17) dorsi-flexion, 55 (SD 19) palmar-flexion, 73 pronation and 67 supination. Grip strength recovered to 85% on average when compared to the opposite hand. There were no deep or superficial wound infections. Three patients had difficulty regaining early hand function, with difficulty complying with physiotherapy. One had borderline mental retardation. Two displayed symptoms of RDS, one responding to medication, and one requiring guanethidine arm block.

Conclusions Intra-articular distal radius fractures can be reliably and anatomically reduced and stabilized using fragment-specific fixation. Fixation of markedly comminuted fractures is secure enough to allow immediate motion. Clinical and radiographic results are excellent, and patient satisfaction is high. Patient compliance with hand therapy is critical for a good functional result.

Introduction: Previously, in vivo kinematic studies have determined the in vivo kinematics of the femur relative to the metal base-plate. These kinematic studies have reported posterior femoral rollback in posterior stabilized (PS) TKA designs, but the actual time of cam/post engagement was not determined. The objective of this present study was to determine, under in vivo conditions, the time of cam/post engagement and the kinematics of the femur relative to the polyethylene insert.

Methods: Femorotibial contact positions for twenty subjects having a PS TKA, implanted by two single surgeons, were analyzed using video fluoroscopy. Ten subjects were implanted with a PS TKA that is designed for early cam/post engagement (PSE) and ten subjects with a PS TKA designed for later cam/post engagement (PSL). Each subject, while under fluoroscopic surveillance, performed a weight-bearing deep knee bend to maximum flexion. Video images were downloaded to a workstation computer and analyzed at ten-degree increments of knee flexion. Femorotibial contact paths for the medial and lateral condyles, axial rotation and condylar lift-off were then determined using a computer automated model-fitting technique.

Results: Subjects implanted with the PSE TKA experienced, on average, the cam engaging the post at 48° (10 to 80°). Subjects having the PSL TKA experienced more consistent results and did experience engagement in deep flexion (Average 75°). Subjects having the PSE TKA experienced, on average, −5.5 mm (1.5 to −9.3) of posterior femoral rollback (PFR), while subjects having the PSL TKA experienced only −2.6 mm (8.5 to −9.0) of PFR. Subjects having the PSE TKA experienced more normal axial rotation patterns. Nine subjects having the PSE TKA experienced condylar lift-off (maximum = 1.9 mm), while only 4/10 having the PSL TKA experienced condylar lift-off (maximum = 2.7 mm).

Discussion: This is the first study to determine the in vivo contact position of the cam/post mechanism. Subjects having a PSE TKA experienced earlier cam/post engagement than subjects having the PSL TKA. Some subjects did not experience any cam/post engagement throughout knee flexion. Subjects having the PSE TKA experienced more PFR and better axial rotation patterns, but subjects having a PSL TKA experienced lesser incidence of condylar lift-off. Results from this study suggest that there may be an advantage to early cam/post engagement, which leads to more normal axial rotation patterns caused by the medial condyle moving in the anterior direction as the lateral condyle rolls in the posterior direction.

Introduction: Previous in vivo kinematic analyses of the hip joint have determined that femoral head separation from the medial aspect of the acetabular component occurs in metal-on-polyethylene THA. The present study analyzes subjects having either an alumina-on-alumina (AOA),alumina-on-polyethylene (AOP),metal-on-metal (MOM) or metal-on-polyethylene (MOP) THA during gait to determine if the incidence of hip joint separation varies based on articular surface material.

Methods: Forty subjects were analyzed in vivo using video fluoroscopy. Ten subjects had a AOA THA, ten an AOP THA, ten a MOM THA, and ten having a MOP THA. All THA subjects were implanted by two surgeons and were judged clinically successful (Harris hip scores > 90.0). Each subject performed normal gait on a treadmill and an abduction/adduction leg lift maneuver while under fluoroscopic surveillance. The two-dimensional (2D) fluoroscopic videos were converted into 3D using a computer automated model-fitting technique. Each implant was analyzed at varying flexion angles to assess the incidence of hip joint separation.

Results: During gait and the abduction/adduction leg lift, no separation was observed in subjects having an AOA THA or in subjects having a MOM THA. Similar to our previous studies pertaining to subjects having a THA with a polyethylene acetabular insert, all ten subjects having a MOP THA and 6/10 subjects having an AOP THA experienced hip joint separation. The maximum amount of separation was 7.4 mm for a subject having an AOP THA and 3.1 mm for a subject having a MOP THA.

Discussion: This study shows femoral head separation from the medial aspect of the acetabular component can occur in the presence of a polyethylene liner. The femoral head often remains in contact with the liner, hinging superolaterally. Potential detrimental effects resulting from hip joint separation include premature polyethylene wear, component loosening (secondary to impulse loading conditions) and hip instability. Wear may be enhanced due to creation of multidirectional wear vectors or excessive loads due to eccentric femoral head pivoting. The absence of separation observed in AOA and MOM THA designs may be related to increased wettability of these materials and tighter radial tolerances resulting in a cohesive lubrication film. This data may be of value in hip simulation studies to better duplicate wear patterns observed in retrieval analyses and assist in the understanding of the lubrication regime and wear rates in AOA and MOM designs, allowing for the synthesis of prosthetic components that minimize wear and optimize kinematics.

Introduction: Patient specific cementless femoral components for THR were developed as a means of addressing the anatomic variations of the proximal femur and hip joint in an effort to achieve long term implant survival and optimum patient function. Design rules were developed with goals of achieving rigid initial stability, maximal endosteal contact for bone integration, and the precise restoration of hip kinematics.

Methods: Beginning in 1989, this series of cementless titanium implants included proximal circumferential HA coating over a macrotextured surface for biologic fixation. All patients who were candidates for cementless arthroplasty (age < 65, active, or overweight) received a custom femoral component. Forty-nine consecutive primary THR in 39 patients were performed during the study period. No patients died and one patient was lost prior to 10 years; all had well fixed stems at latest follow up. The remaining 38 patients (48 hips), 16 females and 22 males, with average age 54 (28-70) and weight 181 (98-270) at surgery, were evaluated at minimum 10 years (range 10-11).

Results: Average modified Harris Hip Scores were 49 (27-87) pre- and 89 (24-100) postoperatively, with pain scores of 17 (0-40) and 42 (10-44) respectively. All femoral components remain well-fixed (Engh Class 1) at final follow-up. No areas of osteolysis were seen distal to the proximal HA-bone interface. Small, focal areas of probable osteolysis were seen at the implant shoulder (4 cases), at the calcar corner (2 cases), and at both sites (1 case). Complications included four proximal margin femoral fissures recognised at surgery, two patients with dislocation, and one non-fatal PE. Reoperations included six head and liner exchanges; two for recurrent dislocation, and four for excessive wear with associated osteolysis (3 pelvic, 1 femoral); and one for fixation and grafting of a trochanteric nonunion.

Discussion: The use of cementless femoral implants based on individual patient characteristics and a set of strict design rules has resulted in excellent clinical and radiographic results at 10-year follow-up. Recent data with some OTS systems have shown comparable excellent results and have diminished the need for the routine use of custom implants in uncomplicated primary situations. However, this series validates the design concepts of this system, supports its use in more complex situations, and suggests applicability on a routine basis where other available implants may be less than optimal.

Introduction: Conventional approaches to cementless revision THR include cemented and cementless stems, which are graft dependent for initial stability (Type 3 reconstructions), distally fixed extensively porous coated implants and modular implants. CT and radiographic visualization, preoperative planning, and patient specific implant fabrication enable the surgeon to achieve the following objectives simultaneously and without compromise: bypass or fill specific bony defects, implement precisely the surgeon’s individual implant design goals, optimise proximal, distal, or regional fit objectives, achieve supplemental fixation via collars, fluted stems, and targeted ingrowth zones/ treatments, and establish head center, neck length, lateral offset, anteversion angle, and leg length.

Methods: This series of cementless titanium implants achieved initial press-fit fixation on host bone with bony attachment via proximally HA coated macrotextured surface. The extramedullary portion of the implant is designed to restore leg length and normal joint mechanics. The initial 44 consecutive revision hips using this rationale were reviewed for inclusion. At surgery, all femoral reconstructions were completed without resorting to Type 3 structural grafts. Six patients died prior to 10 years f/u, and three (4 hips) were lost. Two stems were removed prior to minimum follow up: one at five weeks post-op for deep sepsis, and one for aseptic loosening presumed secondary to metabolic derangements from poorly controlled end-stage renal disease. The remaining 31 patients (34 hips), 18 females and 13 males with a mean age of 61 (range 31-75) and average weight of 168 (85-240) pounds, were evaluated at minimum 10 years (range 10 to 11 years).

Results: All 34 components remain well-fixed (Engh Class 1) at last follow up (97% implant survival). Stress shielding was uncommon outside the calcar region. Average modified Harris Hip Scores were 49 (10-88) pre-operative and 81 (48-100) at final follow-up, with pain scores of 18 (0-44) and 41 (30-44) respectively. Complications included fracture (intraop: 4 fissures, 2 stable type II, 1 unstable type III, and 1 late periprosthetic fractures distally), and three dislocations.

Discussion: The concept of a metaphysical loading, proximally ingrown, collared patient specific revision implant gave results comparable to Engh’s series of extensively coated revision stems, while avoiding the high failure rate associated with structural allograft, the worrisome proximal bone loss associated with fully porous coated stems, the high cost of modular implants.

Introduction: Understanding the in vivo motions of human joints has become increasingly important. Researchers have used in vitro (cadavers), non-invasive (gait labs), and in vivo (RSA, fluoroscopy) approaches to assess human knee motion. The objective of this study was to use fluoroscopy and computer tomography (CT) to accurately determine the 3D, in vivo, weight-bearing kinematics of normal knees.

Methods: Five normal knees clinically assessed as having no pain or ligamentous laxity were analyzed. Using CT scanning, slices were obtained six inches proximal to the joint line on the femur and six inches of the proximal tibia. Three-dimensional CAD models of each subject’s femur, tibia and patella were recreated from the 3D bone density data. Each subject was then asked to perform five weight-bearing activities while under fluoroscopic surveillance: (1) deep knee bend, (2) normal gait, (3) chair rise, (4) chair sit, and (5) stair descent. The computer-generated 3D models of each subject’s femur and tibiaon (> 1

Aim: To report the early results of the Elite Hylamer hip with Zirconium femoral heads in patients younger than 60 years. Methods: 29 hips were implanted in 26 patients by a single surgeon with a specialist interest in hip arthroplasty. Third generation cementing techniques were used for all implants. All patients have been followed up. There has been one death. Results have been analysed using the life table method using the Peto method for 95% confidence intervals. Results: Mean age 49.2 years (range 31–57). 12 Females and 17 Males.15 of 29 hips (53.3%) have been revised or are currently on the waiting list for revision surgery. These failures have occurred in 7 Females and 8 Males. Mean time to failure 35.4 months (range 18 to 68 months). All failures have been as a result of aseptic loosening. Survivorship analysis reveals a 32.42% survival at 5 to 6 years (6.9% standard error). Conclusions: At the time of its introduction, Hylamer was thought to represent a significant step forward in the reduction of the problem of osteolysis. This however has not been our experience. In the light of the catastrophic failure rate in this series of patients, all postoperative X-rays were critically reviewed. We were unable to observe any dramatic technical errors by way of implant malpositioning and cement mantle deficiencies to account for the observed failures. We have also seen that statistically there is no difference in the hip scores for the patients whose hips have failed and those who have not yet met the criteria for failure. In view of this it is imperative that patients with this implant should be reviewed both clinically and radiologically. We feel that these results should be published earlier rather than later to ensure that others remain vigilant in the follow up of their patients

Aims: The aim of this study was to þnd out if undisplaced displaced distal radial fractures require plaster immobilisation. Methods: In this prospective study, undisplaced distal radial fractures were divided into two groups; plaster immobilisation was used for one group while removable volar splint was used for the other group. Follow up was at six weeks, three months and six months. Patients were assessed by clinical examination, grip strength, radiological assessment, EQ-5D and a Short Form 12 questionnaire. Results: At 3 months, no difference was found between the two groups in clinical evaluation, radiological assessment, the functional outcome, grip strength, and visual analogue score for pain. Conclusions: We conclude that undisplaced distal radius fractures can probably be treated with out a plaster cast and put straight into wrist orthosis.

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.

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.

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 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.

A procedure is presented which allows the efficient production of a patient specific computer model of the femur, for surgical planning. Similar models require long processing times and/or high performance computing.

The method uses 24 key landmark points to customise a generic femur to patient data, using a desktop computer. By using non-linear elements a smooth, curved surface is obtained. A finite element mesh of a generic femur consisting of 384 elements was created using the analysis software CMISS (Bioengineering Institute, University of Auckland). A rectangular shaped host mesh was defined to enclose the generic femur. Datasets of 5 human femurs were obtained using a hand-held laser scanner on dry bones and the visible human dataset. Key landmark data points were selected on the generic femur along with corresponding target points on each data set. The host mesh was then deformed using a least squares algorithm, causing customisation of the generic femur to the patient specific model. Each customised model was compared with its entire dataset. The fitting process took less than 100 seconds on a 180 MHz 02 computer (SGI, CA, USA). The algorithm yielded an average root mean square (RMS) of 3.09mm with a standard deviation of 0.15mm. Operator time for positioning the projection points was less than 5 minutes.

This paper presents a novel means for customisation of human femoral geometry with generation of patient specific models on a PC from scan data in under 10 minutes. Current work is focusing on stress analysis, surgical simulation and planning.