Introduction. Since the introduction of 3rd generation Metal-on-Metal-Hip-Resurfacing-Arthroplasty (MoMHRA), thousands of such prostheses have been implanted worldwide in younger patients with end-stage hip osteoarthritis. However, no independent centre has reported their medium-to-long term outcome. The aim of this study is to report the ten year survival and outcome of the Birmingham Hip Resurfacing (BHR), the most commonly used MoMHRA worldwide. Methods. Since 1999, 648 BHRs were implanted in 555 patients, the majority of which were male (326). The mean age at surgery was 52.1years (range: 17–82), with primary OA as most common indication (85%). Mean follow up was 7.1years (range: 1–11). The Oxford Hip Score (OHS) and UCLA questionnaires were sent to all patients. Implant survival was established, with revision as the end point. Sub-analysis was performed by gender, femoral component size (small: <45mm, standard: 46–52, large: >53mm) and age at surgery (young:<50yrs, old:>50yrs). Results. Preliminary results show that survival and clinical outcome were better in men than women (p=0.013) and in patients with large and standard components compared to small (p=0.005). In women the survival and clinical outcome were worse in the young than the old (p=0.049). In men there was no difference in survival or clinical outcome between the young and old (p=0.106). In young men the 10-year survival was 95%, the mean OHS was 45 and the mean UCLA score was 8.1. Conclusion. The results of resurfacing are good in men. They perform particularly well in the young and highly active men who tend to have problems with conventional hip replacements

The use of Birmingham hip resurfacing (BHR) remains controversial due to the increased revision rate in female patients. We compared the outcomes of BHR in female patients to an age matched total hip arthroplasty(THA) cohort. We reviewed the pain, function and total Harris Hip Scores(HHS), and Kaplan-Meir survivorship for BHR and THA cohorts from a prospective regional arthroplasty database.

There were 234 patients in each cohort, with mean age of 51 years. The BHR cohort had significantly better function and total HHS at all points of the 5-year study, but not for the post-operative pain score. The 5-year revision rate for the BHR cohort was significantly higher than the THA cohort (6.8% vs 3.4%, p=0.001). The main reason for revision in the BHR cohort was aseptic loosening (n=8), followed by metallosis (n=3). The 5-year Kaplan-Meier survivorship was 92.6% (95% CI±1.7%) and 96.4% (95% CI±1.3%) for the BHR and THA cohort (p=0.001).

BHR can give significantly better functional outcomes than THA. The vast majority of female patients were happy with BHR and did not need further surgery at the 5-year stage. This is somewhat at odds with the recent reputation of the procedure. The 10-year result of the same cohort is warranted to provide further data. Our study is not a recommendation to still offer BHR to female patients, but rather to inject a note of realism into the debate. There are implications for future implant development in that these results do validate resurfacing as a functionally valuable option for active patients.

Background

Hip resurfacing arthroplasty (HRA) has seen a recent revival with third generation Metal-on-Metal prostheses and is now widely in use. However, safety and effectiveness of hip resurfacing are still questioned. We systematically reviewed peer-reviewed literature on hip resurfacing arthroplasty to address these issues.

Introduction

Metal-on-metal hip resurfacing (MOMHR) is a good surgical indication for young active patients. However, it cannot be used in patients with an excessively short femoral head/neck. To address these cases, a new surgical technique has been developed comprising femoral head augmentation using impacted morcellized bone grafts.

INTRODUCTION

Although simulation studies have shown superior wear properties of metal-on-metal articulations, increased concern exists regarding the excess in-vivo wear of a small number of Metal-on-Metal-Hip-Resurfacing (MoMHRA) implants. Serum ion levels of Chromium (Cr) and Cobalt (Co) are surrogate markers of wear. Risk factors associated with increased wear include female gender, small components, dysplasia, cup orientation outside safe zone and femoral head downsize during surgery with an associated decrease in Head-Neck-Ratio (HNR). However, these factors are interlinked. This study aims to identify the factors that are most important for subsequent wear of MoMHRA, by performing a multivariate analysis.

Introduction

Although femoral neck fractures remain a concern in short term failures for hip resurfacing, acetabular component position and fixation are increasingly being recognized as causes of mid term failures for hip resurfacing. This study aimed to evaluate the migration pattern of a cobalt chrome, beaded acetabular component for a metal on metal hip resurfacing.

Hip resurfacing has grown rapidly since its introduction in the United States, as an alternative to total hip replacement in the younger, active patient. Some studies have suggested a steep learning curve and a higher complication rate when compared to THR. Existing studies have originated from the pioneering surgeons, using a specific type of resurfacing implant. The purpose of this study was to look at the experience of a single, non-inventor surgeon with the adoption of hip resurfacing, using 3 different implants.

Hip resurfacing arthroplasty is an established and effective intervention for osteoarthritis of the hip in the young active patient, relying on the principle of femoral bone-stock preservation. A recognised mode of failure is neck thinning leading to radiological evidence of neck collapse and clinical failure.

We report on a series of these slow-neck-failure patients and highlight the increased incidence of this phenomenon in post-menopausal female patients. This is a single operator, single implant series; 172 cases were identified from databases at our institution. 76 were female, mean (SD) age 52 (7) years. 96 were male, mean (SD) age 51(12) years. 15 (8.7%) patients required revision. 12 (80%) were female, 9 (75%) of these were due to slow neck failure. In the men one patient developed ALVAL requiring removal of his bilateral hip resurfacings, the other failure mode was early femoral neck failure. Mean time to failure was 6 months in men and 37 months in women. This difference in failure rates is also seen in the NJR figures.

This review confirms the relatively high incidence of premature failure in post-menopausal females. NICE guidance in 2003, currently under review, stated that resurfacing is indicated in male patients up to 65 and female patients up to 60. As a result of this study we are currently advising post-menopausal patients that this risk of early failure may make total hip replacement a preferable option to resurfacing arthroplasty.

Background

Metal on metal hip resurfacing has become popular worldwide for younger patients because of perceived advantages in function and ease of revision, due to bone conservation. Joint Registry data have shown increased risk of early failure, particularly in younger females. There have been few studies comparing the outcome of resurfacing to cemented total hip arthroplasty (THA).

Introduction

Controversy exists as to whether the short external rotator tendons and capsule of the hip should be repaired after posterior approach primary total hip arthroplasty (THA). Recent studies using radiopaque markers have demonstrated that reimplantation of these muscle tendons fail early and may not prevent post operative dislocation.

INTRODUCTION. Hip wear simulator test results could be affected by many non-bearing related factors such as fixation surface conditions, equipment calibration and component set-up. In an effort to improve the accuracy, reliability and repeatability of hip simulator test, a quality management system has been established at the IDC hip tribology laboratory, which has been accredited by UKAS (United Kingdom Accreditation Service) in accordance with the recognised international standard ISO17025. This study demonstrates that under well-controlled laboratory and testing conditions, satisfactory repeatability can be achieved during hip simulator studies. METHODS. Between 2008 to 2010, ten 50 mm Birmingham Hip Resurfacing (BHR) devices were tested by the IDC tribology laboratory using two ProSim hip wear simulators in three different tests (T1, T2 and T3). All tests were performed following the same IDC testing protocols at 1 Hz frequency for 5 million cycles (Mc) or until after a steady state was reached. Paul type stance phase loadings with a maximum load of 3 kN and a swing phase load of 0.3 kN was used. The flexion and extension angles were 30 and 15 degree. The internal/external rotation angel was ±10 degree. Wear was measured gravimetrically using an analytical balance (Mettler, Toledo xp504) with an accuracy of 0.1 mg. RESULTS. Results showed that wear of all the components tested followed the typical biphasic trend of wear for MoM hip joint device with a high “running-in” wear during the initial stage followed by a low “steady state” wear in the later stage. The data points scattered in a narrow range following the same trend line throughout the tests. The maximum difference in accumulated volume loss between any two tests at any given cycle was less in 0.2 mm3. The average running-in wear rates (±SD) were 0.72 ±0.17, 0.86 ±0.01 and 0.71 ±0.19 mm3/Mc respectively for test T1, T2 and T3. The running-in wear rates for test T1 and T3 were identical, whilst that for T2 was slightly higher. In spite of this, the wear rates for the bearings tested in T2 were still in the same range as those tested in T1 and T3 during the running-in stage. The steady state (>1.0Mc) wear rate of three different tests was practically the same, being 0.18 ±0.02, 0.18 ±0.06 and 0.16 ±0.04 mm3/Mc respectively for test T1, T2 and T3. Overall, the mean running-in wear rate was 0.74 ±0.16 mm3/Mc, and the steady state wear rate was 0.17 ±0.04 mm3/Mc for the 10 BHR devices tested in three different studies. DISCUSSIONS. This study shows that satisfactory repeatability can be achieved during hip simulator test of metal on metal hip joint devices. Well controlled test procedures including calibration of testing and measurement equipment, correct and consistence test set-up and attention to non-bearing surfaces are some of the most important prerequisites for reliable and accurate hip simulator test results

INTRODUCTION. Whilst there is a great deal of research on hip implants, few studies have looked at implant orientation and the subsequent effect upon the wear performance of a hip resurfacing. This study aimed to measure implantation angles through radiographic analysis and linear wear for retrieved acetabular cups in order to investigate possible causal links between wear and implant orientation. MATERIALS & METHODS. Seventy Birmingham Hip Resurfacing (Smith & Nephew, UK) cups with known time in vivo were analysed. Linear wear of retrieved cups were assessed using a Talyrond 290 roundness machine. Deviations from the characteristic manufactured profile, was identified as a region of wear. Polar measurements across the wear region were taken to determine wear. The linear wear rate (LWR) of a component was defined as the linear wear (μm) divided by the duration of the implant life in vivo (years). Cups which showed the wear crossing over the edge of the cup were classified as edge loaded (EL). For all non-edge loaded (NEL) cups, the wear area was within the bearing surface. Cup orientation angles were conducted for 31 cups. This was determined by superimposing BHR models of appropriate size, generated by CAD ProEngineer Wildfire 4, onto anterior-posterior x-rays. Anatomical landmarks and specific features of the BHR were used as points of reference to determine cup version and inclination angles. RESULTS. Forty two cups were classed as EL, showing regions of wear extending beyond the edge of the cup. Twenty eight were classed as NEL. The EL group had an average LWR of 25.4(±8.05 95% CL) μm/yr, whilst the NEL group generated an average LWR of 1.45 (±0.34 95% CL) μm/yr, a statistically significant difference (p<0.05).a Following radiographic analysis, 23 cups were classed as EL, showing regions of wear extending beyond the edge of the cup. Eight were classed as NEL. Cups in the EL group showed average inclination and version angles of 54.35° (±5.37° 95% CL) and 22.43° (±5.23° 95% CL). Average inclination and version angles of cups in the NEL group were 45° (±7.20° 95% CL), and 14.88° (±3.38° 95% CL) respectively. Inclination and version angles between the two groups were statistically significant (p<0.05). DISCUSSION. Through linear wear and radiographic analysis, the current study has shown that mal-positioned resurfacing devices classed as EL had higher linear wear than the NEL cups. Edge loaded cups examined in this study showed significantly higher inclination and anteversion (p<0.05) than the non-edge loaded devices. This indicates that component wear is closely associated with in vivo orientation. The success of any implant is dependent upon implant orientation both in version and inclination angles. The correct implant orientation will help to ensure that wear occurs within the bearing surfaces, maintaining an optimal lubrication regime and low wear

INTRODUCTION. Femoral neck narrowing (NN) following Metal-on-Metal Hip Resurfacing Arthroplasty (MoMHRA) is a well-recognised clinical phenomenon. The incidence of resurfaced hips with NN > 10% is reported to be up to 27%. Its pathogenesis is thought to be multi-factorial secondary to stress shielding, impingement, osteolysis secondary to wear/ion particles and as a result of reduced vascularity and pressure effect on cancellous bone secondary to the presence of a soft-tissue mass around the resurfaced hip. Recognised risk factors for its development include: female gender and the presence of a pseudotumour. Serum Chromium (Cr) and Cobalt (Co) are recognised surrogate markers of in-vivo wear of MoMHRA. The aims of this study were to establish whether NN is associated with increased wear. METHODS. A cohort of 214 patients with unilateral MoMHRA (139M: 75F) was included in this study. Primary osteoarthritis was the diagnosis leading to surgery for the majority of patients (208). The average age at surgery was 54.1 years old (13–73). Six different implants were used; BHR (116), Conserve plus (92), Recap (2), ASR (2), Adept (1) and Cormet (1). The average femoral component size was 49.2mm (range: 38–59). The average follow up was 4.3 years (range: 2–10). Patients were subdivided into 3 groups as per implant size. Small size component group had implants <45mm, average size group had components 45–51mm and large component size group had components >51mm. All patients had Prosthesis-Junction-Ratio (PJR) measured from postoperative (PJRpost) and at latest follow up (PJRfollow) radiographs. Measurements were made using the method described by Lilikakis1. Metal ion levels (Cr/Co) were measured at last follow-up for all patients. Cr level >5.1g/ml and Co levels >4.4 g/ml were considered high2 and patients with such levels formed the high ion group. RESULTS. For the whole cohort, mean NN was 3.2% (range: 0–32%, SD:4.3). Females (4.7%, range: 0–32%, SD: 5.8) had significantly greater NN than males (2.4%, range: 0–23%, SD: 2.9) (p=0.001). Patients in the large component group had less NN (2.1%, SD: 2.3) in comparison to the average (3.2%, SD: 3.7%) (p=0.046) and the small (5.9%, SD: 7.9) (p=0.007) component size groups. There was no difference in NN between small and average sized components (p=0.1). Patients in the high ion group (25 patients) had significantly greater NN than patients with low ions (10.1%, range: 1%–32%, SD: 8.3 Vs 2.3%, range: 0–11, SD 2.3) (p<0.0001). NN >10% was seen in 16 hips (7.5%). The odds ratio of having high ions if NN >10% was 125 (p<0.001). DISCUSSION. The findings of this study showed that greater NN occurs in females and patients with small components and in patients with high ions. Furthermore, hips with NN >10% should be investigated further as they are more likely to have increased wear

Endoprosthetic replacement of the proximal femur may be required to treat primary bone tumours or destructive metastases either with impending or established pathological fracture. Modular prostheses are available off the shelf and can be adapted to most reconstructive situations for this purpose. We have assessed the clinical and functional outcome of using the METS (Stanmore Implants Worldwide) modular tumour prosthesis to reconstruct the proximal femur in 100 consecutive patients between 2001 and 2006. We compared the results with the published series for patients managed with modular and custom-made endoprosthetic replacements for the same conditions.

There were 52 males and 48 females with a mean age of 56.3 years (16 to 84) and a mean follow-up of 24.6 months (0 to 60). In 65 patients the procedure was undertaken for metastases, in 25 for a primary bone tumour, and in ten for other malignant conditions. A total of 46 patients presented with a pathological fracture, and 19 presented with failed fixation of a previous pathological fracture. The overall patient survival was 63.6% at one year and 23.1% at five years, and was significantly better for patients with a primary bone tumour than for those with metastatic tumour (82.3% vs 53.3%, respectively at one year (p = 0.003)). There were six early dislocations of which five could be treated by closed reduction. No patient needed revision surgery for dislocation. Revision surgery was required by six (6%) patients, five for pain caused by acetabular wear and one for tumour progression. Amputation was needed in four patients for local recurrence or infection.

The estimated five-year implant survival with revision as the endpoint was 90.7%. The mean Toronto Extremity Salvage score was 61% (51% to 95%). The implant survival and complications resulting from the use of the modular system were comparable to the published series of both custom-made and other modular proximal femoral implants.

We conclude that at intermediate follow-up the modular tumour prosthesis for proximal femur replacement provides versatility, a low incidence of implant-related complications and acceptable function for patients with metastatic tumours, pathological fractures and failed fixation of the proximal femur. It also functions as well as a custom-made endoprosthetic replacement.