Introduction and Aims: To deliver osteogenic cells into bone defects, the crucial steps are cell attachment and migration in cell-delivery biomaterials. The aim of this study was to examine whether complexes comprised of vitronectin (VN), insulin growth factors (IGFs) and insulin growth factor binding proteins (IGFBPs) could enhance human osteoblasts attachment, especially cell migration in three-dimensional (3-D) culture.

Method: Human osteoblasts derived from alveolar bone chips (passage 4–10) and established human osteoblast cell line SaOS-2 were used. These cells were seeded on scaffolds of type I collagen sponges and poly glycolic acid (PGA) (approx. one millimetre thick, porous structure), which had been coated with VN +/− IGF-I +/− IGFBP-3. Cell attachment and migration were evaluated by cell counting, confocal microscopy, and scanning electron microscopy.

Results: The number of attached human osteoblasts was significantly higher in wells in which pre-bound VN was coated on the polystyrene culture dish or on type I collagen sponges. However, no significant difference of cell attachment was observed when growth factors were bound to these surfaces in the presence of VN. In the two scaffold materials examined, greater cell attachment was found in type I collagen sponges compared to PGA scaffolds. However, coating the scaffolds with complexes comprised of VN + IGF-I or VN + IGFBP-5 + IGF-I enhanced cell attachment on PGA. Moreover, the presence of vitronectin + IGF-I + IGFBP-5 resulted in significantly greater osteoblast migration into deep pore areas as compared to untreated scaffolds or scaffolds treated with different combinations of the VN +/− IGF +/− IGFBP-5.

Conclusion: Complexes of VN + IGFBP-5 + IGF-I enhance the attachment and migration of human osteoblast in three-dimensional culture, which implies that this complex has potential application for use in surface modification of biomaterials for tissue reconstruction.

Introduction and Aims: Decreasing blood loss during total hip replacement (THR) remains a challenge for the orthopaedic surgeon. This study investigated the effects of the antifibrinolytics aprotinin and epsilon aminocaproic acid (EACA) against placebo on blood loss during primary total hip replacement. Their safety and mechanism of action was also investigated.

Method: Forty-five patients undergoing primary unilateral total hip arthroplasty were randomised to receive an infusion of either aprotinin, EACA, or placebo. Intra- and post-operative blood loss was measured, as was the rate of blood transfusion and changes in haemoglobin concentration. Clinical examination and duplex ultrasound was used in all patients to detect thrombotic events. All patients were assessed clinically six weeks post-op to detect adverse events. Platelet function was assessed using P-selectin, Platelet-monocyte aggregates (PMA) and factor V/Va levels. D-dimer activity was recorded as an indicator of fibrinolysis. Non-parametric statistical analysis was employed in the interpretation of results.

Results: There was no difference in demographics or pre-operative platelet function between the groups with the exception of the EACA group which had a lower pre-operative haemoglobin concentration. Intra-operative blood loss was significantly lower in the aprotinin group compared to placebo (p=0.01), similarly there was also a reduction in intra-operative blood loss in the EACA group but this did not reach statistical significance. Post-operative bleeding from closed suction drains was markedly reduced for both aprotinin (60%, p=< 0.01) and EACA (53%, p=< 0.001) compared to placebo. Markedly less haemoglobin was lost in drains in both antifibrinolytic groups, with aprotinin showing a 77% (p=< 0.0001) and EACA a 73% reduction (p=< 0.001) in post-operative haemoglobin loss. Despite this, no difference in the rate of blood transfusion was observed between groups. Total hip arthroplasty surgery led to the activation of platelets as evidenced by P-selectin, PMA and factor V/Va levels. However, platelet function was not affected by either aprotinin or EACA. Both antifibrinolytics showed a similar increase in D-dimer levels indicating a similar efficacy in inhibiting fibrinbolysis. There were no DVTs, PEs or infections recorded in the study, and no increase in adverse events was seen with the use of antifibrinolytics.

Conclusion: Infusion of either aprotinin or EACA reduces blood loss after primary THA. Both agents are equally effective and have a favourable safety profile. The two drugs inhibit fibrinolysis in a similar fashion, and this action appears to be independent of platelets.

Introduction and Aims: Cyclic pneumatic pressure applied to the musculature proximal to a fracture of the distal radius has been shown to produce compressive loading of the fracture. The aim of this randomised controlled in vivo study in an ovine model was to investigate the effect of the pneumatic pressure on fracture healing.

Method: Thirty-seven sheep underwent a transverse osteotomy of the right radius. All sheep were managed in a plaster cast and splint to ensure non-weight bearing during rehabilitation. Nineteen of the sheep were randomised to receive cyclic loading by the application of a pressure cuff around the muscles of the proximal forearm deep to the cast. The other 18 sheep acted as controls. The sheep in the experimental group received 120 cyclic loads over two 10-minute sessions each day starting one week post-osteotomy. Sheep from both groups were sacrificed at either four or six weeks. X-rays, ultrasonography, biomechanical testing and histomorphometry were used to assess differences between the groups.

Results: The area of periosteal callus on lateral and antero-posterior x-ray, the peak torsional strength, the fracture stiffness, the energy absorbed over the first 10 degrees of torsion and histomorphometric analysis all showed that the fractures in the group treated with the cyclic pneumatic pressure achieved the same level of union at four weeks as the control group fractures at six weeks (not significantly different p> 0.05). The density of the woven bone in the periosteal callus of the treated sheep was significantly greater than the controls (p< 0.01). Ultrasonography showed no significant difference (p> 0.05) in the amount of muscle wasting between the treated group and the control group.

Conclusion: This study has shown that the rate of healing is enhanced when cyclic pneumatic pressure is applied to the musculature proximal to a transverse fracture of the distal radius in an adult sheep model. There is potential for this treatment to be used in a human population.

Introduction and Aims: The radiographic appearance of fractures is often used as an evaluative tool when assessing the status of healing fractures. The aim of this study was in the first instance to assess the reliability of orthopaedic surgeons to measure the area of periosteal callus and secondly to compare the area with the biomechanical strength of the fractures.

Method: Thirty-seven sheep underwent a transverse osteotomy of the right radius. All sheep were managed in a plaster cast and splint to ensure non weight-bearing during rehabilitation. Nineteen of the sheep were ran-domised to receive cyclic loading by the application of a pressure cuff around the muscles of the proximal forearm deep to the cast. The other 18 sheep acted as controls. Sheep from both groups were sacrificed at either four or six weeks. Fractures were x-rayed and subjected to biomechanical testing following sacrifice. X-rays were transferred to a Labview program from which the area of callus was measured. Biomechanical testing of the fractures was a torsional test to failure. The peak torque, stiffness and energy absorbed over the first 10 degrees of torsion were measured for each fracture.

Results: The two orthopaedic surgeons who measured the area of callus showed a positive correlation (r = 0.85). When the four-week fractures that were treated with cyclic loading were compared with the four-week control fractures, the periosteal callus measurement along with the peak torque, fracture stiffness and energy absorbed over the first 10 degrees of torsion all showed a significant difference (p < 0.05). In addition, when the six-week fractures that were treated with cyclic loading were compared with the six-week control fractures, the periosteal callus measurement along with the peak torque, fracture stiffness and energy absorbed over the first 10 degrees of torsion were not significantly different (p > 0.05).

Conclusion: The results show that the area of periosteal callus on radiographs can be related to the biomechanical status of a healing fracture. Further research is required to determine if other characteristics of the periosteal callus plus quantification of the callus area is able to accurately predict fracture strength.

Introduction and Aims: Surgery for degenerative lumbar spondylolisthesis may entail both decompression and fusion. The knee-chest position facilitates decompression, but fixation in this position risks fusion in kyphosis. This can be avoided by intra-operative re-positioning to the fully prone position. We aim to quantify restoration of lordosis achieved by this manoeuvre.

Method: Thirty-six patients with degenerative lumbar spondylolisthesis and stenosis were treated by posterior decompression and interbody fusion with pedicle screw fixation (without interbody cages). There were 16 men and 20 women with a mean age of 58.2 years (32–80). The decompression, interbody grafting and screw insertion were performed with the patient in the knee-chest position. The patient was repositioned to the fully prone position for subsequent fusion. The sagittal plane angle was measured on the pre-operative, intra-operative and post-operative x-rays. Short-Form 36 (SF-36) scores and Visual Analogue Scales (VAS) for pain (0 to 10) were determined pre- and post-operatively.

Results: Twenty-eight patients underwent single-level fusion, two patients had two levels, two patients had three levels and four patients had four levels fused. The mean pre-operative sagittal angle between the operated vertebrae was 15.7 degrees lordosis, and the intra-operative angle before re-positioning was 14.9 degrees. The mean immediate post-operative angle was 23.7, and at six-month follow-up the angle was 23.1. Overall there was a mean increase in lordosis angle after repositioning of 8.0 degrees per operative level (p< 0.01). The mean scores of the SF-36 improved in all eight domains and this was significant (p< 0.05) for social functioning (44.4 to 68.9), energy and vitality (36.0 to 49.5), pain (23.8 to 58.3) and general health perception (51.4 to 65.6). Mean VAS pain scores for back pain improved from 7.47 pre-operatively to 3.84 post-operatively (p< 0.001); and for leg pain improved from 7.56 to 3.78 (p< 0.001). No complications attributable to the manoeuvre occurred.

Conclusion: Lumbar spondylolisthesis was found to be associated with reduction of normal lumbar lordosis. The knee-chest position for surgery exacerbates this loss of lordosis. Intra-operative repositioning restores lordosis to greater than the pre-operative angle, which may improve clinical outcome.

Introduction Experimental heterotopic bone formation in the canine urinary bladder has been observed for more than seventy years without revealing the origin of the osteoinductive signals. In 1931, Huggins demonstrated bone formation in a fascial transplant to the urinary bladder. Through an elaborate set of experiments, it was found that proliferating canine transitional epithelial cells from the urinary system act as a source of osteoinduction.

Urist performed a similar series of experiments in guinea pigs as Huggins did in his canine model. After two weeks, mesenchymal cells condensed against the columnar epithelium and membranous bone with haversian systems and marrow began to form juxtapose the basement membrane. At no time was cartilage formation noted, only direct membranous bone formation. They also demonstrated the expression of BMP’s in migrating epithelium and suggested that BMP is the osteoinductive factor in heterotopic bone formation.

Method This study was approved by Institutional Animal Ethics Committee. Six dogs underwent a mid-line laparotomy incision followed by mobilisation of a right sided myoperitioneal vascularised flap based on an inferior epigastric artery pedicle. A sagittal cystotomy is made in the dome of the bladder and the vascularised flap was sutured in place with acryl absorbable, continuous suture. The animals were sacrificed at 6 weeks. The bladder samples were removed and assessed by histology and immunohistochemistry. Sections were incubated with optimal dilution of primary antibody for type I collagen, type III collagen, alkaline phosphatase (ALP), bone morphogenetic protein (BMP)-2 and –4, osteocalcin (OCN), osteopontin (OPN), bone sialoprotein (BSP).

Results The mechanism for bone formation induced by the epithelial-mesenchymal cell interactions is not clear. We were able to demonstrate mature lamellar bone formation 6 weeks after transplanting a portion of the abdominal smooth muscle into the bladder wall. The bone formed immediately adjacent to the proliferating transitional uroepithelium, a prerequisite for bone formation in Huggins’ model. Here we report evidence of cartilage formation and therefore endochondral ossification as well as membranous bone formation. This is very similar histologically to the process of endochondral ossification at the growth plate in the growing skeleton. We propose a mechanism for the expression of BMP by epithelial cells.

Discussion This study demonstrates transitional epithelium induced formation of chondrocytes and osteoblasts in muscle tissue. The sequential expression of bone matrix proteins was related to cell proliferation, differentiation and formation of endochondral and membranous bone. Further information regarding the molecular mechanism of bone formation induced by epithelial-mesenchymal cell interactions will improve understanding of cell differentiation during osteogenesis.

Introduction Over recent years the techniques of femoral and acetabular impaction allografting with fresh frozen morsellised bone have become incressingly popular for revision total hip arthoplasty with osseous defects. In many centres lack of availability or legislation has required surgeons to explore alternatives to fresh frozen bone that may have different structural and biological properties. In this study we compare in vitro the load carrying capacity of irradiated morsellised bone against a control non-irradiated sample.

Methods Fresh frozen heads were divided in halves with one half irradiated at 25 kGy and the control half left non-irradiated. A custom-built pneumatic loading apparatus applied a force of 1200N at a cycle rate of 1Hz for a total of 1500 cylcles. This loading cycle was chosen to simulate the loads normally experienced by the human femur during walking gait. The reduction in height (subsidence) of each test specimen was measured and statistical analysis performed.

Results Results from each treatment group displayed similar patterns of subsidence, with an initial rapid rate of subsidence occurring up to 50 to 100 load cycles, followed by a more gradual, slower rate as the tests progressed. The results for each treatment (mean ± standard deviation) were −3.59 ± 0.91 mm and −2.98 ± 0.812 mm for the irradiated and non-irradiated groups, respectively (P+0.049). The irradiated specimens demonstrated an increased amount of subsidence compared to the non-irradiated specimens.

Conclusions This study has shown that gamma irradiation of morsellised bone allograft material decreases its load-carrying capacity, as expressed by an increase in subsidence due to an applied cyclic load. The ability for morsellised bone allograft material to bear applied loads in vivo is an important biomechanical parameter and one indicator of a successful clinical outcome. The clinical implications of this result are important when considering the most appropriate methods of treating human bone allograft material.

In relation to the conduct of this study, one or more of the authors is in receipt of a research grant from a commercial source.

Introduction This study aims to improve knee arthroplasty prosthetic alignment by determining if an algorithm based on establishing the most prominent points on the medial and lateral malleolion 3D CT scans can be used to establish the true center of the ankle joint.

Methods Axial, coronal and sagittal multi-planar reconstructions were generated on 20 ankles. Two observers independently identified the most prominent medial and lateral malleolar points, in the coronal plane, and the highest talar dome point, in the sagittal plane. Ratios were calculated comparing total intermalleolar distance to distance to medial and lateral malleolus, and the ratio of medial to lateral distance. The distance from the true center of the joint, in the sagittal plane, to the computer calculated center was determined. Statistical analysis using ANOVA, paired t-tests and regression analysis was performed. There were 17 normal ankles, two arthritic ankles, and one previously fractured ankle.

Results In the coronal plane there was a strong correlation between the measurements of each observer. The mean intermalleolar distance was 70.2 mm (95% CI 68.3–72.0). The strongest correlation was seen in the ratio of lateral distance to total distance (r=0.728) which was 0.57 in normal ankles (95% CI 0.55–0.58). The ratio for arthritic ankles was 0.48 (95% CI 0.46–0.50) and for the fractured ankle 0.57 (95% CI 0.15–0.99). These were significantly different at the five percent level (p< 0.02). The normal ankle ratio was substantiated by regression analysis. There was a poor correlation between the individual measurements in the sagittal plane (r=0.218). The mean distances from the calculated line to the true center were not statistically different with the true center always lying posterior to the calculated line (4.2 mm (95% CI 2.5–5.9) and 2.8 mm (95% CI 1.7–3.8) posterior. For the combined data this means that the mean distance that the true center of the ankle joint’s from a line joining the medial and lateral malleoli is 3.2 mm (95% CI 2.3–4.0 mm). The data was reproducible with a small standard deviation in each plane. Assuming a 300 mm tibial length, angular error in tibial alignment generated by a computer navigation system is less than one degree in both planes.

Conclusions The algorithm presented can give accurate measurements of normal ankle joints in knee navigation surgery.

Introduction: Vertebroplasty using polymethylmethacrylate (PMMA) is an established technique in the treatment of osteoporotic fractures of the vertebra. Complications of vertebroplasty associated with PMMA leakage can include damage to the spinal cord. Previous studies have sought to investigate thermal changes in the paravertebral region, but used smaller volumes of cement than are used clinically¹, or used in vitro experimental techniques.² We have designed an in vivo sheep model to investigate the thermal changes after injection of clinically relevant volumes of PMMA, and to measure change in cord function associated with PMMA extrusion.

Methods: Five sheep were anaesthetised and 1.0ml of PMMA was injected into the spinal canal at the L1 level, with measurement of the temperature by thermocouple. The L2 to L5 vertebral bodies were then exposed and 9 thermocouples placed at points in and around the vertebra (superior and inferior endplate, disc above and below, central body, posterior wall, and spinal canal) to measure paravertebral temperature for a 10- minute period after injecting 6.0mls of PMMA. All animals were then humanely euthanased, and the T12 to L2 vertebrae harvested to examine the effect of temperature on the vertebral body and spinal cord using light microscopy.

Results: The experiments showed significant increases in the paravertebral temperature, especially at the end-plates (mean temperature 51.7°C, mean increase in temperature +16°C). This is contrary to studies using small cement volumes or in vitro conditions. Intradiscal and posterior wall temperature did not significantly rise. Spinal canal temperature reached a mean 75.4°C in the presence of “extruded” cement. Microscopic examination showed thermal damage to the spinal cord.

Discussion: The experiments indicate that neurological complications associated with vertebroplasty are likely to be thermally mediated, and that the analgesic effects of vertebroplasty are likely to be, at least in part, due to thermal damage to endplate neurological structures.

Introduction Unicompartmental knee replacement (UKR) is an increasingly utilised alternative to tibial osteotomy and total knee arthroplasty in patients with single compartment degenerative disease. We report on four fractures of the medial tibial plateau following UKR.

Methods We retrospectively reviewed four cases with periprosthetic tibial plateau fractures following unicompartmental knee replacement. Each arthroplasty, performed between 1999 and 2002, was done in a community teaching hospital by a single orthopaedic surgeon and a senior level assistant. All patients had medial compartment osteoarthritis confirmed both radiographically and arthroscopically prior to arthroplasty surgery. The arthroplasties were performed by four different surgeons and three different arthroplasty systems were used. All cases were reviewed using the documented chart histories and x-ray evaluation. Each surgeon was contacted individually for the relevant case history and x-rays. The study population was composed of four females, and no males with a mean age of 63.5 years (range 58 to 68). Two patients (50%) had simultaneous bilateral UKRs performed. The remaining two patients had unilateral procedures, involving one right and one left knee. Two patients were clinically obese, and one patient had had a previous ipsilateral high tibial osteotomy.

Results The total number of fractures was four, involving three left knees and one right knee. Of the bilateral arthroplasties each patient sustained a unilateral fracture of the left knee. The patient with the previous tibial osteotomy sustained an ipsilateral fracture. Two fractures involved traumatic falls, the remaining fractures had no history of trauma. The mean post-operative period to fracture was 95.75 days with a range of 5 to 195 days. Two patients had revision surgery to total knee arthroplasty. One patient underwent internal fixation of the fracture with retention of the original prosthetic components and exchange of the polyethylene bearing. The remaining patient underwent revision of the tibial component with concurrent internal fixation and was subsequently revised to total knee arthroplasty as the result of failure. Subsequent to the described surgery all fractures have healed with no further surgical intervention.

Conclusions This series, whilst small, demonstrates that tibial periprosthetic fracture following UKR is a previously unreported but important cause of failure. Revision surgery to total knee replacement appears to be a reasonable salvage option.

Introduction Correct component positioning is critical for the stability of the prosthesis in total hip arthroplasty (THA). Malpositioning of either the femoral or acetabular component may lead to impingement or dislocation. This study aims to assess the accuracy of placement of the acetabular component in THA.

Methods Forty-six total hip arthroplasties were studied. The surgeon’s estimates of intra-operative inclination and anteversion of the acetabular component were recorded. Post-operative inclination of the acetabular component was measured from routine plain antero-posterior (AP) radiographs of the pelvis. Planar anteversion of the acetabular component was determined from AP radiographs with the beam centred over the hip using the method described by Pradhan. Planar anteversion was then corrected to ‘true’ anteversion correcting for inclination. The surgeons estimate of intra-operative cup inclination and anteversion and the radiographic position were compared.

Results The mean difference between the estimated and true cup inclination was 1.5° more than planned (range of −13° to 16°, SD 6.75). The mean difference between estimated and true values of anteversion was 1.8° less than planned (range of −32° to 25°, SD 11.07). Allowing plus or minus five degrees of error, 37% of the cups were outside the estimated inclination and 35% outside the estimated anteversion. There was a poor correlation for both inclination (Spearman’s correlation coefficient equals 0.20) and anteversion (Spearman’s correlation coefficient equals 0.25) between perceived and true cup positioning. Using the ‘safe zones’ for inclination and anteversion described by Lewinnek et al for minimising dislocation, 48% of the cups were unsafely positioned in either inclination, anteversion or both.

Conclusions Our study showed that positioning of the ace-tabular component cannot be reliably performed even by experienced surgeons. Acetabular component placement is of high importance for preventing dislocation or impingement. A tool, such as a navigation device, may be beneficial in improving acetabular component placement.

In relation to the conduct of this study, one or more of the authors is in receipt of a research grant from a non-commercial source.

Introduction Component malalignment may result in failure in total knee arthroplasty (TKA). Knee navigation systems assist surgeons with intra-operative component positioning in TKA. We report on the effect of one system on the post-operative mechanical axis of the limb and coronal alignment of femoral and tibial components in TKA.

Methods In a prospective study of 47 total knee replacements we compared 24 cases using conventional techniques to 23 cases using the Stryker Knee Navigation System. Patient groups were matched for sex, weight and age. Postoperative antero-posterior radiographs of the whole leg were used to determine the mechanical axis of the limb and coronal position of the femoral and tibial components.

Results The mean post-operative mechanical axis of the limb in the navigated group was 1.3° varus (range 7° varus to 3.5° valgus, SD=2.6). In the control group the mean mechanical axis was 0.8° varus (range 9.5° varus to 10° valgus, SD=4.4). There was no significant difference in the mean mechanical axis between the groups (p=0.6). There was no significant difference in mean coronal alignment of the femoral (p=0.99) or tibial components, (p=0.98). The 95% confidence interval for the mechanical axis was narrower for the navigated group (2.4° varus to 0.2° varus) than for the control group (2.6° varus to 1.1° valgus). Using Levene’s test (not dependant on normal distribution) the variances for the mechanical axis of the limb, and the coronal alignment of the femoral and tibial components are all significantly less in the navigated than non-navigated groups (p=0.05, 0.001 and 0.004 respectively).

Conclusions This study showed no difference in the overall mean alignment of navigated versus non-navigated knees. However, a significant decrease in the variance of alignment seen with navigation means we are seeing fewer outlying results that may lead to a decrease in mechanical failure in TKA.

In relation to the conduct of this study, one or more of the authors is in receipt of a research grant from a non-commercial source.

Introduction Malposition of the acetabular component in total hip arthroplasty is associated with a number of significant complications. In this study we acertain the accuracy of an imageless computer based surgical navigation system for positioning the acetabular component, using a mechanical hip device.

Methods A mechanical hip device was constructed that allowed accurate measurement of inclination and version, leg length and lateral offset of the acetabular and femoral components. In 31 cases these parameters were varied while a blinded operator would place the cup in the predetermined position in the mechanical hip jig. The values given by the navigation system on the screen were recorded and compared to the measurements obtained directly from the mechanical hip device.

Results The mean difference between value set by an independent person and value read by the navigation system was; inclination of the cup 0.97 ± 0 and the ante-version of the cup 1.58 ± 0.83. The leg length change contributed by the cup showed a mean difference between beforehand set value and read value on the screen of 1.48 ± 1.36 mm and for lateral offset change by the cup of 1.58 ± 0 mm.

Conclusions The accuracy of the hip navigation unit demonstrated in this study is well within the limits that would be required for clinical usage as a surgical aid in total hip arthroplasty and could provide the surgeon with a tool that enables significant improvement in accuracy for acetabular positioning.

Introduction Using a new surgical technique for the first time involves a ‘learning curve’. The aim of this study is to assess the technical errors encountered in the early utilisation of a computer assistance system during total knee arthroplasty and to see if this error rate decreases with experience.

Methods Thirty-two total knee replacement procedures performed by a single surgeon using the Stryker Knee Navigation system for the first time, were monitored. All technical difficulties were documented. We compared the complications encountered in the first five cases against the following 27 cases.

Results Technical difficulties related to the navigation equipment were noted in four of the 32 cases (12.5%). These included (one case each); errors in tibial pin placement, concern over initial navigation readings, pin loosening, and dropping the navigation shim plate. There was a significant decrease in technical difficulties encountered in the later cases (7%) compared to the first five cases (40 percent, p= 0.041). Additionally, in three of the 32 cases (9%) the surgeon used their clinical judgement to override the navigation readings and recut the bone, to take ligament balancing into account.

Conclusions A steep learning curve is involved when first utilising the Stryker Knee Navigation system. It is recommended that adequate training is undertaken prior to utilising knee navigation. The computer readings should be considered carefully and clinical judgement should not be overridden.

In relation to the conduct of this study, one or more of the authors is in receipt of a research grant from a non-commercial source.

Introduction Concentric interference screw placement has been proposed as having potentially better biological graft integration than eccentric interference screw placement during soft tissue ACL reconstruction. The purpose of this study was to determine whether a wedge shaped concentric screw was at least equivalent to an eccentric screw in stiffness, yield load, ultimate load and mode of failure.

Methods Seven matched pairs of human cadaveric tendon in porcine tibia with titanium wedge shaped screws were randomly allocated to either the eccentric or concentric groups. Bone tunnels were drilled 45° to the long axis of the tibia, akin to standard ACL reconstruction. Tendon diameter was matched to tunnel diameter and a screw one millimetre larger than tunnel diameter was inserted. An Instrom machine was used to pull in the line of the tendon. Tendons were inspected after construct disassembly.

Results The concentric screw configuration showed significantly higher stiffness (p< 0.0085), yield load (p< 0.0135) and ultimate load (p< 0.0075). The mode of failure in the eccentric screw position was slippage at the screw tendon interface in all cases. In the concentric group 88% of cases had a breakage in the tendon and 13% of cases had slippage at the tendon bone interface. However, it was observed during construct disassembly that there was more macroscopic damage to the tendon substance in the concentric group. Failure was mostly by tendon breakage, which reflects the strongest fixation possible with the tendon being the weakest link in the system.

Conclusions Concentric interference screw fixation of soft tissue graft offers superior fixation in single pullout mode when compared to eccentric interference screw fixation.

Introduction The reduced WOMAC function scale has been developed and initial validity performed. However, further validation and recommendations for the treatment of missing values is required. The aim of this study is to further assess the validity of the reduced function scale of the WOMAC and recommend a protocol for the treatment of missing values.

Method Further validation of the reduced scale was performed via a cross-over study of 100 pre-operative total joint replacement patients, each being randomised to receive either the full or reduced scale along with the pain scale, and then the alternate version upon admission. Data utilised in the development of the reduced scale was used to develop a missing value protocol, where the number of valid responses for several protocols was examined, as well as comparison of the means and standard deviations. Of the consenting 100 patients, 66 continued onto admission. The median time between administrations of the questionnaires was 14 days (range zero to 72 days).

Results There was no significant difference between pain scores for each questionnaire using the paired t-test (p=0.56). Similarly, there was no significant difference between the full and reduced function scales (p=0.65). The standard protocol for the full scale is that if there are four or more missing items, the patient’s response is invalid. But when there are one to three items missing, the average value for the sub-scale is substituted in lieu of these missing values. Examining the frequencies of valid responses, means and standard deviations when using different missing value protocols (none missing, zero or one, up to two and up to three missing), indicated that there was no substantial benefit between the ‘up to two’ missing and ‘up to three’ missing response protocols. However, for this small gain, the supposition that the completed items are representative of the missing ones rises from 29% (two of seven items) to 43% (three of seven items) should be considered unacceptable.

Conclusions The reduced WOMAC function scale has been further validated. It is proposed that where three or more responses are missing, the patients response is regarded as invalid. Where there are one or two items missing, the average value for the sub-scale is substituted in lieu of these missing values.

Introduction: The aim of this study was to compare the serum cobalt and chromium levels in patients with Oxford Universal hips and Cenator hips. Both systems are composed of cobalt chromium alloy and have modular cobalt chromium heads, however only the Oxford hip has a sliding mechanism.

Material: The serum levels of chromium and cobalt were measured in 20 patients with Oxford Universal Hip replacement (Group 1). This was compared to the serum levels of chromium and cobalt in 17 patients with Cenator Hip replacement (Group 2) and 20 patients with no implants (Group 3). Patients in Group 1 and 2 were assessed clinically and with plain radiographs. Patients were excluded if there was evidence of loosening, if they had other joint implants or any other known cobalt or chromium implant and if they had impaired renal function. All hip replacements were performed as primary procedures. Specimens were analysed by electrothermal atomization atomic absorption spectrometry.

Results: There was no statistically significant difference in serum cobalt and chromium levels between groups 1 and 2. Patients in groups 1 and 2 had statistically significant higher serum levels of chromium and cobalt than group 3 patients.

Discussion: This study demonstrates that serum levels of chromium and cobalt are elevated in patients with stable hip implants composed of this alloy but not in a normal population. Although it is not known what the long-term effects of chronic low-grade exposure to these ions are, these levels are many order of magnitude below the toxic range. Furthermore, our results show that the Oxford Universal Hip releases no more metal ions into the circulation than an implant without a sliding mechanism.

Purpose: The purpose of the study is to compare the disease severity at the time of surgical intervention between patients undergoing primary joint replacement under the National Health Service and Private Health-care Systems.

Materials: 166 patients were included in the study – 101 NHS and 65 Private. Inclusion criteria were: 1) hip or knee osteoarthritis, 2) primary joint replacement, and 3) informed consent of the patient. Patients with arthropathy of inflammatory, infectious or neoplastic aetiology were excluded. Physician evaluation included medical history, calculation of Charleson Comorbidity Scores, and Knee Society rating. Patients were given self-assessment health questionnaires including WOMAC, SF-36, and Nottingham Health Profile.

Results: Mean age was 69.4 years and did not vary significantly between NHS and Private groups. Charleson Comorbidity Scores were significantly worse in the NHS group than in the private. Health assessment questionnaire scores were all adjusted for age, sex, and comorbidity. In NHS patients undergoing TKR, we demonstrate significantly worse pre-operative comorbidity than in private group for indices of function and pain. Patients undergoing THR showed little difference in pre-operative comorbidity.

Conclusion: NHS patients undergoing primary TKR have significantly more advanced disease than their counterparts who are privately insured. Access to TKR surgery is determined by the healthcare delivery system rather then a threshold level of disease severity. Further follow-up of the outcomes of TKR in these two groups needs to be carried out to determine the long-term effects of accessing surgical care at a more advanced stage of disease.

Temporary immobilisation of joints can lead to permanent ankylosis or fusion. The aim of this study is to demonstrate that treatment of vertebral fractures by single level fusion and 2 level fixation preserves movement in the unfused lower motion segment after removal of metalwork.

12 consecutive thoracolumbar fractures were treated by posterior fixation over two motion segments with fusion of the upper injured segment. Average age 39 years (27–50yrs.) and 6 were male. L2 was most frequently affected (6) then T12 (3), L1(2) and L3(1). Using the Denis classification 9 were Burst type B, 1 was Burst type A and 2 were Compression type B. No patients had abnormal neurology or any other vertebral injury. All operations were performed by one surgeon (RC) within 7 days of injury. Metalwork bridging the injured vertebra was removed at mean 11 months (8–13 * one patient 27 months) and average follow up in this study was 12 months (2–40) after removal of metalwork. A simple pain questionnaire and flexion-extension radiographs were obtained. The average movement in the motion segment previously bridged by metalwork was 5 degrees (0–12). For comparison, the level below moved an average of 7 degrees (2–17). Kyphus angle was 11 degrees (1–18) on presentation corrected to 0 degrees at operation (−6 - +12) returning 1 year after removal of metalwork to 5 degrees (1–16). Pain scores (0–10) were measured retrospectively, prior to the accident mean 0(0–1) and at review 2.6 (0–6).

Only one patient failed to return to previous employment. She had the highest pain score at 6, showed no movement at the bridged motion segment where removal of metalwork was delayed to 27 months.

Introduction: Octacol F15 is a fibrin sealant, derived from human cryoprecipitate, which can be delivered as a spray that seals on contact. Pre-clinical studies have established its safety. The aim of this study was to determine the impact of Octacol F15 on blood loss in patients undergoing THR

Materials and Methods: The effect of Octacol F15 on 81 patients undergoing THR was studied in a randomised, prospective, multi-centres study. 38 patients received Octacol F15 delivered to the soft tissues around the hip at 3 predetermined times throughout the operation. 43 patients received a routine THR. Surgeons were constrained to use their predetermined approach, fixation method, and DVT prophylaxis. Blood loss was measured and transfusion needs recorded along with all adverse events.

Results: Mean blood loss in treatment patients was 699ml v 837ml in controls. Log transformed means adjusted for weight, surgeon and pre-operative haemoglobin showed a significant reduction in blood loss of 197ml or 23.5% (95% CI 5.4% to 38.1%) as an effect of treatment (p=0.014). Intra-operative blood loss was not significantly less in the treatment group (p=0.13) but post-operative blood loss was significantly reduced (p=0.0005). 11 treatment patients received blood transfusions (29%) against 18 controls (42%). This difference in transfusion needs was not significant (p=0.11). There was only one minor complication ‘possibly’ related to the use of Octacol F15.

Conclusion: Octacol F15 significantly reduces blood loss in THR without any increase in the complication rate. Its use in THR, particularly in procedures in which increased bleeding may be encountered, offers important clinical benefits.