Introduction Metal-on-Metal Hip Resurfacing (MMHR) has been established as a successful alternative to Total Hip Replacement (THR). However, several series report a 2 % incidence of early femoral neck fractures. Avascular necrosis (AVN) was considered to be responsible for the majority of observed fractures, raising concerns about the femoral head blood supply during MMHR. This study aims to further understand the mechanisms of femoral blood flow restriction by monitoring gas levels (O2) during the operative procedure.

Methods Patients undergoing MMHR using the posterior approach were evaluated. Following division of fascia lata, a guide wire was introduced up the femoral neck, aiming for the anterosuperior quadrant of the head. It was then removed. A calibrated gas-measuring electrode was inserted in the created bone channel. X-ray confirmation was obtained to ensure that the active measurement area of the electrode was 2–3cm below the femoral surface. O2 and N2O levels were then continuously monitored throughout the operation.

Results A preliminary analysis of four patients is presented: Stable N2O- measurements throughout the procedure confirmed valid electrode measurements. Baseline oxygen concentration levels of 40%– 60% were detected before division of short rotators. After hip dislocation oxygen concentration dropped in all patients to levels ranging between 0% and 5%. Oxygen concentration was found to remain depressed at these levels throughout the entire operation in three patients. Recovery of O2 concentration to baseline levels was observed in one patient 15 minutes after dislocation.

Discussion In three patients the extended posterior approach and joint dislocation had a dramatic effect on the perfusion in the femoral head. These patients have a high risk for development of AVN and potential femoral neck fracture. Whilst the results require further verification, subsequent experiments will determine if less invasive procedures or specific positioning of the limb can protect the femoral blood supply.

Introduction: The Charnley Elite femoral component was first introduced in 1992 as a new design variant of the original Charnley femoral component (De Puy, Leeds, UK) with modified neck and stem geometry. The original component had undergone few changes in nearly forty years and has excellent long-term results.

Early migration of the new stem design was determined by Roentgen Stereophotogrammetric Analysis (RSA). Rapid early migration of a component relative to the bone, measured by RSA, is predictive of subsequent aseptic loosening for a number of femoral stems. As there was rapid early migration and rotation of the Charnley Elite stem, we predicted that the long-term results would be poor. An outcome assessment is required as stems of this type are still being implanted.

Materials and method: One hundred Charnley Elite stems, implanted in our centre between 1994 and 1997 were included in a prospective, cross-sectional follow-up study. Outcome measures include validated clinical scores (Charnley hip score, Harris hip score and Oxford hip score) and radiological scores (Gruen classification) as well as revision rates over the past 10 years.

Results: The preliminary analysis results are given. The mean time to follow-up was 8.28 years. 20 patients have died due to causes unrelated to their operations. 10 patients had stem revisions: 9 for aseptic loosening and 1 for a peri-prosthetic fracture. This indicates a significant 10% failure rate of the prosthesis in less than 10 years.

Preliminary clinical scores in the patients who had not undergone any subsequent surgery were adequate (Oxford Hip Score mean average of 23.9).

Thirteen percent of radiographs analysed had evidence of loosening, giving an overall loosening rate of 14% at 8 years.

Discussion and conclusion: The clinical follow-up supports the RSA predictions of early failure of the Charnley Elite femoral stem.

Background: Hip dysplasia is a complex developmental process. Untreated acetabular dysplasia is the most common cause of secondary hip osteoarthiritis. With increased interest in redirectional pelvic osteotomies, the role of the shelf procedure needs to be re-defined.

Aim of the study: to investigate the effectiveness of the shelf procedure in adults with symptomatic acetabular dysplasia by assessing the functional and radiological outcome at a minimum of five years follow-up.

Material and Methods: Seventy-six consecutive adults with symptomatic acetabular dysplasia treated with acetabular shelf augmentation, have been followed up for an average period of 11 years (range: 6–14). The mean age was thirty-three years (range: 17–60 years). The Oxford hip score (OHS) was used for clinical assessment. Centre-edge angle (CEA) and acetabular angle (AA) were measured to determine femoral head coverage. Osteoarthiritis severity was based primarily on the width of the joint space using the De Mourgues classification. Survivorship analyses using conversion to THR as an endpoint were performed. logrank test was used to compare the outcome of the shelf against the variables of age, preoperative osteoarthiritis, preoperative and postoperative AA, CEA angles.

Results: The shelf procedure improved the mean preoperative CEA from 11° (range: 20° to 17°) to 50° postoperatively (range: 30° to 70°) and the mean preoperative AA from 52° (range: 46° to 64°) to 32° postoperatively (range: 18° to 57°). The Mean OHS was 34.6 (hip score maximum: 48). Thirty percent of hips needed THR at an average duration of 7.3 years. Survival analysis using conversion to THR as an endpoint was 86% (CI, 76%–95%) at five years and 46% (CI, 27%–65%) at ten years. The survival in the 44 patients with only slight or no joint space narrowing was 97% (CI, 93%–100%) at 5 years and 75% (CI, 51%–100%) at 10 years. This was significantly higher (p= 0.0007) than the survival in the 32 patients with moderate or severe osteoarthiritis, which was 76% (CI, 55%–89%) at 5 years and 22% (CI, 5%–38%) at 10 years. There was no significant relationship between survival and age (p= 0.37), pre and postoperative centre-edge angle (p= 0.39), or acetabular angle (p= 0.85).

Conclusion: Shelf acetabuloplasty is a reliable, safe procedure offering medium-term symptomatic relief for adults with acetabular dysplasia. The best results were achieved in patients with slight or no joint space narrowing.

We inserted an electrode up the femoral neck into the femoral head of ten patients undergoing a metal-on-metal hip resurfacing arthroplasty through a posterior surgical approach and measured the oxygen concentration during the operation. In every patient the blood flow was compromised during surgery, but the extent varied. In three patients, the oxygen concentration was zero at the end of the procedure. The surgical approach caused a mean 60% drop (p < 0.005) in oxygen concentration while component insertion led to a further 20% drop (p < 0.04). The oxygen concentration did not improve significantly on wound closure. This study demonstrates that during hip resurfacing arthroplasty, patients experience some compromise to their femoral head blood supply and some have complete disruption.

We followed up 76 consecutive hips with symptomatic acetabular dysplasia treated by acetabular shelf augmentation for a mean period of 11 years. Survival analysis using conversion to hip replacement as an end-point was 86% at five years and 46% at ten years. Forty-four hips with slight or no narrowing of the joint space pre-operatively had a survival of 97% at five and 75% at ten years. This was significantly higher (p = 0.0007) than that of the 32 hips with moderate or severe narrowing of the joint-space, which was 76% at five and 22% at ten years. There was no significant relationship between survival and age (p = 0.37) or the pre- and post-operative centre-edge (p = 0.39) and acetabular angles (p = 0.85).

Shelf acetabuloplasty is a reliable, safe procedure offering medium-term symptomatic relief for adults with acetabular dysplasia. The best results were achieved in patients with mild and moderate dysplasia of the hip with little arthritis.

Introduction: The Birmingham Hip Resurfacing (BHR) is a metal on metal prosthesis with no published independent clinical studies. It is increasingly used as an alternative to stemmed prostheses in younger patients.

This study presents the 2 year migration results of the BHR femoral component using Roentgen Stereophoto-grammteric Analysis (RSA).

Methods: 26 hips in 24 subjects underwent a BHR, through the postero-lateral approach using CMW3G cement. RSA marker balls were placed in the cortical bone of the femur intra-operatively. The femoral component migration was measured at intervals of 3, 6, 12 and 24 months postoperatively using the Oxford RSA system. The implants were un-modified, geometric algorithms were used to identify the femoral component.

Results: The BHR femoral component showed no significant displacement from its immediate post-operative position. All components of migration showed no significant displacement in any direction, at 1 or 2 years.

Conclusion: The BHR femoral component does not migrate significantly within the first two post-operative years. Its’ migration compares favourably to other designs of femoral component. The BHR is therefore likely to remain stable in the future, as the majority of implant migration occurs within the first two years.

Polished, tapered stems are now widely used for cemented total hip replacement and many such designs have been introduced. However, a change in stem geometry may have a profound influence on stability. Stems with a wide, rectangular proximal section may be more stable than those which are narrower proximally. We examined the influence of proximal geometry on stability by comparing the two-year migration of the Exeter stem with a more recent design, the CPS-Plus, which has a wider shoulder and a more rectangular cross-section. The hypothesis was that these design features would increase rotational stability.

Both stems subsided approximately 1 mm relative to the femur during the first two years after implantation. The Exeter stem was found to rotate into valgus (mean 0.2°, sd 0.42°) and internally rotate (mean 1.28°, sd 0.99°). The CPS-Plus showed no significant valgus rotation (mean 0.2°, sd 0.42°) or internal rotation (mean −0.03°, sd 0.75°). A wider, more rectangular cross-section improves rotational stability and may have a better long-term outcome.

We describe a technique of ‘cross-hip distraction’ to reduce a dislocated hip with subsequent reconstruction of the joint for septic arthritis with extensive femoral osteomyelitis. A 27-year-old woman presented with a dislocated, collapsed femoral head and chronic osteomyelitis of the femur. Examination revealed a leg-length discrepancy of 7 cm and an irritable hip. A staged technique was used with primary clearance of osteomyelitis and secondary reconstruction of the hip. A cross-hip monolateral external fixator was used to establish normal anatomy followed by an arthroplasty. A good functional outcome was achieved. The use of cross-hip distraction avoids soft-tissue and nerve damage and achieved improved abductor function before arthroplasty.

We present the histological findings of bone retrieved from beneath the femoral components of failed metal-on-metal hip resurfacing arthroplasties. Of a total of 377 patients who underwent resurfacing arthroplasty, 13 required revision; for fracture of the femoral neck in eight, loosening of a component in three and for other reasons in two. None of these cases had shown histological evidence of osteonecrosis in the femoral bone at the time of the initial implantation.

Bone from the remnant of the femoral head showed changes of osteonecrosis in all but one case at revision. In two cases of fracture which occurred within a week of implantation, the changes were compatible with early necrosis of the edge of the fracture. In the remaining six fractures, there were changes of established osteonecrosis. In all but one of the non-fracture cases, patchy osteonecrosis was seen.

We conclude that histological evidence of osteonecrosis is a common finding in failed resurfaced hips. Given that osteonecrosis is extensive in resurfaced femoral heads which fail by fracture, it is likely to play a role in the causation of these fractures.

Aim: To investigate the functional and radiological outcome of shelf acetabuloplasty in adults with significantly symptomatic acetabular dysplasia, with a minimum of a 5 year follow-up.

Material and Methods: 77 consecutive shelf procedures (68 patients) with an average follow-up of 10.9 years (range: 6–17) were reviewed. The Oxford hip score (OHS) was used for clinical assessment. Centre-edge angle (CEA) and acetabular angle (AA) were measured as indicators of joint containment. The severity of osteoarthiritis was based primarily on the extent of joint space narrowing. Survivorship analyses using conversion to THR as an endpoint were performed. Logrank tests were used to compare the survivorship of the shelf procedure against the variables of age, preoperative osteoarthiritis, pre and postoperative AA, CEA angles.

Results: The average age at time of surgery was 33 years (range: 17–60). At the time of the last follow-up, the mean OHS was 34.6 (maximum score: 48). Mean postoperative CEA was 55 (Pre-operatively: 13 degrees) while mean postoperative AA was 31 (Pre-operatively: 48 degrees). Thirty percent of hips needed THR at an average duration of 7.3 years. The survival in the 45 patients with only slight or no joint space narrowing was 97% (CI, 93%-100%) at 5 years and 75% (CI, 51%-100%) at 10 years. This was significantly higher (p≤= 0.0007) than the survival in the 32 patients with moderate or severe osteoarthiritis, which was 76% (CI, 55%-89%) at 5 years and 22% (CI, 5%-38%) at 10 years. There was no significant relationship between survival and age, pre and postoperative AA, CEA angles (p> 0.05).

Conclusion: Shelf-acetabuloplasty offers symptomatic relief to adults with acetabular dysplasia but overall deteriorates with time. About 50% of the patients do not need THR for over 10 years. Best results with shelf-acetabuloplasty were achieved in patients with slight or no joint narrowing.

Purpose of the study: To evaluate the clinical outcome of revision total hip arthroplasty (THA) using the Oxford Hip prosthesis combined with impaction allografting. Methods and results: The Oxford hip is a trimodular prosthesis with a polished tapered metaphyseal section that is free to slide on the stem. The stem is inserted uncemented into the diaphysis, bone graft is impacted proximally, with mesh if necessary, and then the proximal wedge is cemented in.

Between 1999 and 2002, we revised 72 hips in 69 patients using this technique (mean age 65years, 28 to 88). Fifty-six cases had aseptic loosening, 8 had infection (2 stages), 7 had peri-prosthetic fractures and 1 had a broken stem. The mean time to revision was 8.5years (1 to 21). Patients were assessed clinically and with the Oxford Hip Score (OHS) pre- and post-operatively. Fifty-seven patients also had acetabular revision. Four patients required femoral osteotomy to remove the old prosthesis. We used a mean of 1.8 (1 to 4) femoral heads per operation.

Complications included 6 peri-operative femoral fractures diagnosed at operation and fixed successfully, 6 infections, 10 dislocations (2 were recurrent), one deep vein thrombosis, 2 pulmonary embolism and one gastrointestinal haemorrhage. The average blood transfusion was 1.8 units (0 to 9).

The OHS improved from 45 (26 to 58) pre-operatively to 24.3 post-operatively (12 to 43). No hip has been re-revised for aseptic loosening at a mean follow-up of 32.7 months (16 to 51).

Conclusion: Although we accept that this is only a preliminary experience, we believe that the use of the trimodular Oxford stem combined with minimal proximal impaction allografting was found to be a reliable method and a successful way of dealing with revision femoral surgery. The results were comparable with a primary arthroplasty in terms of pain relief and functional results

There is an increasing interest amongst surgeons and demand from patients for hip resurfacing. One concern regarding resurfacing is the incidence of femoral neck fracture post operatively. McMinn and Treacy report an incidence of 0.4% in their series, our finding was of an incidence of over four times as high (1.9%). We looked at our database of hip resurfacings and tried to identify the risk factors for fracture.

We identified 11 fractures and compared these with 22 controls selected by choosing the cases performed by the surgeon immediately before and after the fracture case. We analysed their medical notes and x-rays. Statistical analysis was performed using a package in ™Excel. The implants were either Birmingham Hip (Midland Medical Technologies) or Cormet (Corin) resurfacings.

No statistically significant correlation was found for sex, age or body mass index. We found that fracture was twice as likely in the presence of possible or probable osteopenia. We did not find that fracture was more likely to occur in patients with a previous diagnosis of Perthes, DDH, SUFE and avascular necrosis (AVN).

We found patients with a superior overhang of the femoral component on the neck did not risk fracture, however we could not demonstrate that notching in itself increased the risk of fracture.

There was no correlation with neck-shaft and stem-shaft angle or neck lengthening and offset and subsequent neck fracture.

In 13 bilateral cases there was fracture in 3 (incidence 23%). Apart from one fracture that occurred at 18 weeks post-operatively all the others occurred before eight weeks. Five fractures occurred in patients who subsequently on histological analysis were found to have avascular necrosis.

We conclude that bilateral surgery is probably unwise. That a superior overhang seems to protect against fracture as long as this is not at the expense of creating an inferior notch. Finally, we find AVN in a number of retrieved heads, what is the true incidence of AVN and does the approach adopted cause the avascular process and if so why do we see so few fractures?

Introduction: A new procedure has been recently adopted to implant the Oxford medial unicompartmental arthroplasty (UCA). All cases are now implanted through a short incision without dislocation of the patella. The aims of this study were to assess the one-year results using this new technique and to determine if the outcome is dependent on surgical experience.

Method: The first 104 Oxford UCA’s (Phase 3) implanted by six surgeons under the care of two consultants were reviewed at one year. All operations were performed using the new technique. The average age at surgery was 68 years. All knees were scored pre-operatively and at review with the American Knee Society score. The cohort was divided into two groups; the first ten cases for each surgeon were included in a ‘learning’ group, whilst the remaining cases were included in an ‘experienced’ group.

Results: Overall the average ‘knee score’ improved from 37 points to 94 and the average ‘functional score’ from 50 points to 92. Average maximum flexion improved from 117° to 131°. The ‘knee score’ for the ‘learning’ group was 91 points. This was significantly less (p = 0.008) than the score of the ‘experienced’ group (96 points).

Conclusions: These results are significantly better than the best historical results of the Oxford (UCA), performed through an open approach with dislocation of the patella.

Despite impressive overall results at one year, lower knee scores were associated with a surgeons ‘learning curve’. After this ‘learning curve’, increased surgical experience led to further improvement with 90% achieving an excellent result, 8% a good, 2% a fair and 0% a poor result.

Polyethylene wear remains an important cause of failure in knee replacements. Retrieval studies, simulators and simple X-ray methods produce wear data that may be inaccurate or unrealistic. We have developed an accurate RSA system for measuring wear in-vivo. Using this system we have found wear rate in a fixed bearing TKR to be about 0.1mm/yr[1]. In this abstract we extend the study to fully congruent mobile bearings.

Four Oxford uni-compartmental knee replacements, with excellent clinical results were studied ten years after implantation. RSA X-rays were taken in double leg stance with the knee in full extension and 15 and 30 degrees flexion. Following RSA calibration, silhouettes of the components on the stereo X-rays were extracted using a Canny edge detector and were matched to silhouettes projected using CAD models to determine the 3D component position. The average minimum thickness of the bearing was determined and was compared with the measured minimum thickness of 14 unused bearings to calculate linear penetration.

The average linear penetration after average 10 years implantation (range 8.5 to 10.25 years) was 0.16 mm (SD 0.13 mm). The average penetration rate was 0.017 mm/year (SD 0.011 mm/year). The maximum linear penetration rate was 0.027 mm/year.

The penetration rate is similar to that obtained in a retrieval study [2]. Compression of the bearing is minimal due to 6sqcm of contact area. This study therefore demonstrates that polyethylene wear on the upper and lower surfaces is minimal in fully congruous mobile bearing knee replacements.

Aim: Small amounts of subsidence may be beneficial in stabilising a stem & appears to be a featue of polished tapered stems. Stem rotation (measured as posterior head migration) within the cement mantle, however, is probably a more important mechanism of failure than subsidence. Stems with a wider proximal portion are thought to better resist rotation. The CPS (Endoplus, UK) is such a device; here we compare its’ stability with that of the Exeter (Stryker-Howmedica, UK). Method: 20 patients received the CPS-plus stem & underwent RSA examinations at 3, 6 & 12 months postoperatively. The Exeter 1 year migration data (32 hips) was used as a comparison. Both groups underwent a Hardinge approach & the prosthesis was secured with CMW3G cement. Results: Both stems subsided about 1mm. The CPS showed less medio-lateral & A-P movement of the proximal stem than the Exeter over 1 year, as shown below: 1 Year Mean Migration ± SEM (mm) Discussion: The CPS internally rotates less than the Exeter, as demonstrated by the smaller amount of posterior head migration. It has a lateral flare of the shoulder; making its’ cross-section wider than the Exeter’s, this probably produces a greater resistance to rotation. The CPS also undergoes less medio-lateral proximal stem migration. Its’ lateral shoulder flare is probably responsible for this axial subsidence, as it prevents the shoulder from moving laterally whilst subsiding onto the calcar.

Increasing the width of the proximal section of a polished tapered stem enhances its rotational stability.

Aims: To determine the pathological changes in the femur following resurfacing hip arthroplasty and identify possible causes of early failure. Methods: Bone samples from 8 femoral heads at several levels were examined histologically following removal of cemented femoral head surface replacement following aseptic early failure: 4 neck fractures (no history of fall), 3 persistent severe pain and 1 cup loosening. Intra-operatively no obvious macroscopic causes of failure (including notching the neck) were noted. In all patients, the initial diagnosis had been osteoarthritis. None had known risk factors for osteonecrosis. Results: In the patients who had recent fracture, the bony changes were suggestive of relatively longstanding osteonecrosis with degenerative, necrotic and þbrotic changes in the bone marrow and loss of osteocyte nuclei in the trabeculae. There was appositional new bone formation at the surface of the necrotic bone trabeculae. The changes were consistent with osteonecrosis of more than 2 weeks duration and probably preceded the fracture in all cases. In the patients who underwent revision for non-fracture, some osteonecrosis was seen, but this was a lot less than when a fracture had occurred. Conclusion: Osteonecrosis of the femoral head is seen following resurfacing hip arthroplasty and may be a predisposing factor in patients who subsequently fracture.

The Birmingham hip resurfacing (BHR) arthroplasty is a metal-on-metal prosthesis for which no medium- or long-term results have been published. Despite this, it is increasing in popularity as an alternative to stemmed prostheses for younger patients. Since the fixation of the socket is conventional, the major concern is long-term failure of the femoral component. This can be predicted by the use of roentgen stereophotogrammetric analysis (RSA). We have therefore undertaken such a study of the BHR femoral component over a period of two years.

Twenty patients (22 hips) underwent a standard BHR procedure. Migration of the femoral component was measured by RSA at intervals of three, six, 12 and 24 months. At 24 months the total three-dimensional migration of the head was 0.2 mm. This was not statistically significant. Previous studies have shown that implants which loosen quickly have rapid early migration. Our results therefore suggest that the BHR femoral component is an inherently stable device which is likely to perform well in the long term.

Introduction: Persistent acetabular dysplasia is a recognized cause of premature hip arthritis. Treatment options include joint preservation (acetabuloplasty/osteotomy) or salvage procedures (THR). Presence of a deficient acetabulum and an elevated acetabular centre make THR technically demanding with uncertain outcome. Shelf ace-tabuloplasty is a viable option, however, most reports in the literature focus on results in children and adolescents.

Aim: To investigate the functional and radiological outcome of shelf acetabuloplasty in adults with significantly symptomatic acetabular dysplasia.

Material and Methods: 77 consecutive shelf procedures (68 patients) with an average follow-up of 10.9 years (range: 6–17) were reviewed. The Oxford hip score (OHS) was used for clinical assessment. Centre-edge angle (CEA) and acetabular angle (AA) were measured as indicators of joint containment.

Results: The average age at surgery was 33 years (range: 17–60). At the time of last follow-up; the mean OHS was 34 (maximum score: 48). Mean postoperative CEA was 59 (Pre-operatively: 16.2 degrees) while mean postoperative AA was 31 (Pre-operatively: 47.5 degrees). Thirty percent of hips needed THR at an average duration of 7.3 years. Pre-operative arthritis was present in 32 hips out of which 17 (53 percent) needed THR. Out of the remaining 45 hips, only 6 (13 percent) needed THR. No correlation was found between the acetabular indices and the outcome.

Conclusion: Shelf-acetabuloplasty offers symptomatic relief to adults with acetabular dysplasia and can delay the need for THR for over 10 years. Best results with shelf-acetabuloplasty were achieved in patients without preoperative arthritis.

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

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

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

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

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

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

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

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

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

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

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

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

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

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.

Before proceeding to longer-term studies, we have studied the early clinical results of a new mobile-bearing total knee prosthesis in comparison with an established fixed-bearing device. Patients requiring bilateral knee replacement consented to have their operations under one anaesthetic using one of each prosthesis. They also agreed to accept the random choice of knee (right or left) and to remain ignorant as to which side had which implant. Outcomes were measured using the American Knee Society Score (AKSS), the Oxford Knee Score (OKS), and determination of the range of movement and pain scores before and at one year after operation.

Preoperatively, there was no systematic difference between the right and left knees. One patient died in the perioperative period and one mobile-bearing prosthesis required early revision for dislocation of the meniscal component.

At one year the mean AKSS, OKS and pain scores for the new device were slightly better (p < 0.025) than those for the fixed-bearing device. There was no difference in the range of movement.

We believe that this is the first controlled, blinded trial to compare early function of a new knee prosthesis with that of a standard implant. It demonstrates a small but significant clinical advantage for the mobile-bearing design.

This early study examines the influence of a wider shoulder on the 1 year migration of a cemented, polished, tapered stem, using RSA.

Polished, tapered stems (PTS) have excellent 10 year survival rates. RSA studies have demonstrated that these devices subside about 1 mm / year. Small amounts of subsidence are beneficial in stabilising a stem. Stem rotation (measured as posterior head migration) within the cement mantle is probably a more important mechanism of failure than subsidence. Stems with a wider proximal portion are thought to better resist rotation. The CPS (Endoplus, UK) is such a device; here we compare its’ stability with that of the Exeter.

20 patients received the CPS-plus stem and underwent RSA examinations at 3, 6 and 12 months postoperatively. The Exeter 1 year migration data was used as a comparison. Both groups underwent a Hardinge approach with CMW3G cement.

Both stems subsided about 1mm. The CPS showed less medio-lateral and A-P movement of the proximal stem than the Exeter over 1 year, as shown below:

The CPS internally rotates less than the Exeter, as demonstrated by the smaller amount of posterior head migration. It has a lateral flare of the shoulder; making its cross-section wider than the Exeter’s, this probably accounts for its’ greater resistance to rotation. The CPS also undergoes less medio-lateral proximal stem migration. Its’ lateral shoulder flare is probably responsible for this axial subsidence, as it prevents the shoulder from moving laterally whilst subsiding over the calcar.

A PTS with a broad proximal section is more stable, this may confer an increased survival advantage.

Purpose: As part of the step-wise introduction of a meniscal-bearing total knee replacement (Oxford TMK) we needed to know, before proceeding to longer term studies, whether its early clinical results were at least as good as those of an established fixed bearing device (AGC).

Material and Methods: With ethical approval, patients requiring bilateral knee replacement for osteoarthritis consented to have the operations under one anaesthetic using one of each prosthesis; to accept random choice of knee; and to remain ignorant which side was which. American Knee Society Scores, Oxford Knee Scores, ROM and pain scores were to be recorded preoperatively and at one year. By January 2001, 40 patients had reached one year and data is available for 36.

Results: Preoperatively there was no difference between the two knees. One patient died in the peri-operative period.

Results at one year (TMK first): AKSS(Knee) 91.6 / 84.1 (p=0.003), OKS 39.8 / 37.6 (p=0.006), ROM 104 / 104 (p=0.364), Pain (AKSS) 47.3 / 41.7 (p=0.01), Pain (OKS) 3.5 / 2.9 (p=0.006).

Conclusion: The TMK performed as well as the AGC. Its AKSS, OKS and pain scores were significantly better. We believe this controlled, blinded trial is the first to have compared the function of a new knee prosthesis with a standard implant before marketing; and the first to have demonstrated a significant clinical advantage for a meniscal-bearing over a fixed bearing TKR. The comparison of bilateral implants in the same patient can reveal significant differences while putting at risk many fewer subjects than would be needed for a classical twocohort RCT.

The Oxford hip score (OHS) is a patient-based instrument for assessment of outcome which is often used after total hip replacement, and the EuroQol 5D (EQ5D) is a patient-based generic questionnaire for health assessment. In an analysis of the outcome at one year of 609 revision hip replacements (RHRs), we compared the OHS and EQ5D scores, postoperative patient satisfaction and change in pain. About 25% of the operations were repeat RHRs. At one year, 57% of patients were very pleased with their operation. The correlation between preoperative and postoperative scores and change scores for the OHS and EQ5D was high. For both instruments the effect sizes were large, but the greater effect size of the OHS suggests that it is particularly sensitive to improvements after RHR. The effect scores of the OHS declined with the number of previous RHRs, while those for the EQ5D seemed less sensitive. Our results confirm the value of the OHS in assessing outcome after RHR.

Ultrasound examination has been recommended for the evaluation of acute haemorrhages into soft tissues or joints in haemophilic patients. We have reviewed the notes of all such patients admitted during one calendar year and find that in 47 separate admissions the ultrasound examination assisted management decisions on 27 occasions. The technique is described with an analysis of the ways in which ultrasound observations may influence the clinician.