Objectives

Modern metal-on-metal (MoM) hip resurfacing arthroplasty (HRA), while achieving good results with well-orientated, well-designed components in ideal patients, is contraindicated in women, men with head size under 50 mm, or metal hypersensitivity. These patients currently have no access to the benefits of HRA. Highly crosslinked polyethylene (XLPE) has demonstrated clinical success in total hip arthroplasty (THA) and, when used in HRA, potentially reduces metal ion-related sequelae. We report the early performance of HRA using a direct-to-bone cementless mono-bloc XLPE component coupled with a cobalt-chrome femoral head, in the patient group for whom HRA is currently contraindicated.

We report a 12- to 15-year implant survival assessment of a prospective single-surgeon series of Birmingham Hip Resurfacings (BHRs). The earliest 1000 consecutive BHRs including 288 women (335 hips) and 598 men (665 hips) of all ages and diagnoses with no exclusions were prospectively followed-up with postal questionnaires, of whom the first 402 BHRs (350 patients) also had clinical and radiological review.

Mean follow-up was 13.7 years (12.3 to 15.3). In total, 59 patients (68 hips) died 0.7 to 12.6 years following surgery from unrelated causes. There were 38 revisions, 0.1 to 13.9 years (median 8.7) following operation, including 17 femoral failures (1.7%) and seven each of infections, soft-tissue reactions and other causes. With revision for any reason as the end-point Kaplan–Meier survival analysis showed 97.4% (95% confidence interval (CI) 96.9 to 97.9) and 95.8% (95% CI 95.1 to 96.5) survival at ten and 15 years, respectively. Radiological assessment showed 11 (3.5%) femoral and 13 (4.1%) acetabular radiolucencies which were not deemed failures and one radiological femoral failure (0.3%).

Our study shows that the performance of the BHR continues to be good at 12- to 15-year follow-up. Men have better implant survival (98.0%; 95% CI 97.4 to 98.6) at 15 years than women (91.5%; 95% CI 89.8 to 93.2), and women < 60 years (90.5%; 95% CI 88.3 to 92.7) fare worse than others. Hip dysplasia and osteonecrosis are risk factors for failure. Patients under 50 years with osteoarthritis fare best (99.4%; 95% CI 98.8 to 100 survival at 15 years), with no failures in men in this group.

Cite this article: Bone Joint J 2014;96-B:1298–1306.

Introduction: In contrast to degenerative (OA) and inflammatory arthritides which are primarily joint surface diseases, femoral head osteonecrosis (ON) is a bone substance disease which extends to the surface. Is HR effective in ON?

Methods: This is a single-surgeon retrospective consecutive case-series with a 5 to 15-year (mean 9.5) follow-up of 95 patients (104 hips) with Ficat-Arlet III/IV ON treated with HR. Mean age is 43 (18 – 68) years. Two patients died from unrelated causes and none is lost to follow-up. Revision of either component for any reason was the end-point. Patients were assessed clinically and with hip function scores and anteroposterior, cross-table lateral radiographs.

Results: Ten failures (1 fracture, 6 femoral head collapse, 2 infections, 1 cup loosening) give a failure rate of 9.6% and 89% survivorship. All the above have been converted to total hip arthroplasty (THA). In one further patient the femoral component has tilted into varus. No other patient shows clinical or radiological adverse signs.

Discussion and Conclusion: Several studies in THA suggest that the results are generally worse in patients with ON compared to those with OA. Others find no difference. Our results show that the cumulative survival of HR in osteonecrosis is worse than that with other diagnoses. Further collapse of the femoral head is the most common reason for failure and it occurred between 3 and 9 years after implantation. HR was originally an option for hip joint surface disease such as OA. ON being a substance problem is in our hands a relative contraindication to hip resurfacing.

Introduction: Metal ion release from metal-metal (MM) joints continues to cause concern. Blood metal levels are a measure of systemic exposure. The usefulness of plasma and erythrocyte levels rests on whether individual variability in these blood fractions is within acceptable limits.

Methods: 461 concurrent specimens of whole blood (WB), plasma and erythrocytes from a heterogeneous group of patients with large and small diameter MM hip arthroplasties were analysed using high resolution mass-spectrometry. 41 specimens were excluded because the level was below the limit of detection. Agreement was assessed with scatter plots, mean differences and Bland and Altman limits of agreement. A p value of d0.05 was considered significant.

Results: Mean differences between WB and its fractions were statistically highly significant (p< 0.001). The scatter showed that the variability in plasma chromium was worse at lower levels and that in erythrocytes was worse at higher levels. Bland analyses showed the limits of agreement extended from −106% to 74% for cobalt and −108 to 158% for chromium and −58% to 46% for cobalt and −63% to 52% for chromium in erythrocytes and plasma respectively. Erythrocyte chromium distribution in the erythrocytes shows no increase with increasing chromium levels in WB.

Discussion: and Conclusion: The variability with plasma and erythrocytes compared to WB metal ion levels rejects the hypothesis that these can be used as surrogate measures of systemic exposure. There appears to be a cellular ceiling beyond which chromium entry into the cell is resisted. This makes erythrocyte levels particularly unsuitable as markers of systemic chromium exposure.

Hip simulators have been used for ten years to determine the tribological performance of large-head metal-on-metal devices using traditional test conditions. However, the hip simulator protocols were originally developed to test metal-on-polyethylene devices. We have used patient activity data to develop a more physiologically relevant test protocol for metal-on-metal devices. This includes stop/start motion, a more appropriate walking frequency, and alternating kinetic and kinematic profiles.

There has been considerable discussion about the effect of heat treatments on the wear of metal-on-metal cobalt chromium molybdenum (CoCrMo) devices. Clinical studies have shown a higher rate of wear, levels of metal ions and rates of failure for the heat-treated metal compared to the as-cast metal CoCrMo devices. However, hip simulator studies in vitro under traditional testing conditions have thus far not been able to demonstrate a difference between the wear performance of these implants.

Using a physiologically relevant test protocol, we have shown that heat treatment of metal-on-metal CoCrMo devices adversely affects their wear performance and generates significantly higher wear rates and levels of metal ions than in as-cast metal implants.

Second-generation metal-on-metal bearings were introduced as a response to the considerable incidence of wear-induced failures associated with conventional replacements, especially in young patients. We present the results at ten years of a consecutive series of patients treated using a metal-on-metal hip resurfacing. A distinct feature of the bearings used in our series was that they had been subjected to double-heat treatments during the post-casting phase of their manufacture. In the past these bearings had not been subjected to thermal treatments, making this a unique metal-on-metal bearing which had not been used before in clinical practice.

We report the outcome of 184 consecutive hips (160 patients) treated using a hybrid-fixed metal-on-metal hip resurfacing during 1996. Patients were invited for a clinicoradiological follow-up at a minimum of ten years. The Oxford hip score and anteroposterior and lateral radiographs were obtained. The mean age at operation was 54 years (21 to 75). A series of 107 consecutive hips (99 patients) who received the same prosthesis, but subjected to a single thermal treatment after being cast, between March 1994 and December 1995, were used as a control group for comparison.

In the 1994 to 1995 group seven patients (seven hips) died from unrelated causes and there were four revisions (4%) for osteolysis and aseptic loosening. In the 1996 group nine patients died at a mean of 6.9 years after operation because of unrelated causes. There were 30 revisions (16%) at a mean of 7.3 years (1.2 to 10.9), one for infection at 1.2 years and 29 for osteolysis and aseptic loosening. Furthermore, in the latter group there were radiological signs of failure in 27 (24%) of the 111 surviving hips.

The magnitude of the problem of osteolysis and aseptic loosening in the 1996 cohort did not become obvious until five years after the operation. Our results indicate that double-heat treatments of metal-on-metal bearings can lead to an increased incidence of wear-induced osteolysis.

We describe the findings at six years in an ongoing prospective clinicoradiological and metal ion study in a cohort of 26 consecutive male patients with unilateral Birmingham Hip Resurfacing arthroplasties with one of two femoral head sizes (50 mm and 54 mm). Their mean age was 52.9 years (29 to 67). We have previously shown an early increase in the 24-hour urinary excretion of metal ions, reaching a peak at six months (cobalt) and one year (chromium) after operation. Subsequently there is a decreasing trend in excretion of both cobalt and chromium. The levels of cobalt and chromium in whole blood also show a significant increase at one year, followed by a decreasing trend until the sixth year.

Introduction: Hip Resurfacing has always been an attractive concept for the treatment of hip arthritis in young patients. Excellent early and medium-term results have been reported with the Birmingham Hip Resurfacing (BHR) device in single and multi-surgeon all-diagnoses and OA series. In the present report we present the results of BHR in inflammatory arthritis.

Methods: This is a single-surgeon consecutive series. There were 15 consecutive hips (12 patients) including 2 women (2 hips) with ankylosing spondylitis (AS) operated at a mean age of 41.7 years (range 29.5 to 54.3 years). Fortytwo hips (31 patients) with seronegative or rheumatoid (RA) arthritis treated with a BHR at a mean age of 40 (13 to 64) years and a follow-up of 2 to 9 (mean 5.9) years were also studied. One patient died 5 years later. Revision for any reason was the end-point and unrevised patients were assessed with Oxford hip scores and reviewed clinico-radiologically with AP and lateral radiographs.

Results: In the RA group there was one failure from femoral neck fracture two months after operation giving a failure rate of 2.4%. There were no failures in this cohort at a follow-up of 1.8 to 8.8 (mean 4.9) years. As a combined group the failure rate of BHRs in inflammatory arthritis is 1.75% and the cumulative survivorship at 9 years is 98.2% (figure).

Discussion: The good results of Birmingham Hip Resurfacing in inflammatory arthritis in this relatively young cohort of patients make this a viable treatment option for these patients. Selection of patients with a reason-able bone quality and adherence to precise operative technique are vital to the success of this procedure.

Introduction: The potential adverse effects of metal ion elevation in patients with metal-metal bearings continue to be assessed. We reported earlier that metal ions cross the placenta. The present report is a comparison of the rate of transfer in 14 study patients (with MM devices) and 24 control subjects (with no metal devices).

Methods: Whole blood from concurrent specimens of maternal and umbilical cord blood obtained at the time of delivery were analysed with high resolution inductively coupled plasma mass spectrometry.

Results: Cobalt and chromium were detectable in all specimens in the control subjects and study patients. The mean difference between maternal and cord blood cobalt concentrations was 0.56 μg/l (p < 0.001) in the study group and 0.03 μg/l (p > 0.5) in the control group respectively (figure). The mean difference between maternal and cord blood chromium concentrations was 0.96 chromium (p < 0.0005) in the study group and 0.002 chromium (p > 0.5) in the control group respectively. The mean cord cobalt in the study patients was significantly higher than that in the control subjects (difference 0.38μg/l, p < 0.01) but the difference in the cord levels of chromium between study and controls (difference 0.13μg/l, p> 0.05) was not significant.

Discussion: There was almost no difference between the maternal and cord blood levels in the control group implying that the placenta offers almost no resistance to their passage in subjects without a metal device. In the study patients the mean cord cobalt level was 59% of the maternal level and the mean cord chromium level was 26% of the maternal level suggesting that the placenta exerts a modulatory effect on the rate of metal transfer when the maternal levels are higher

Introduction: The Birmingham Hip Resurfacing (BHR) device was introduced in 1997 as a conservative hip arthroplasty option for young patients with severe arthritis. Primary osteoarthritis is the most common etiology of hip arthritis in the West. Excellent early and medium-term results have been reported with the BHR. This is a 9–year review of the first 100 consecutive BHRs performed by one surgeon (DJWM) for primary OA.

Methods: The first 100 BHRs (91 patients) performed for OA are now at a mean follow-up of 9.1 (range 8.9 to 9.3) years. Four patients (5 hips) died 5.2 to 6.9 years later due to unrelated causes. Patients with unrevised hips were reviewed clinico-radiologically and with questionnaire assessment.

Results: With revision for any reason as the end-point there were four failures (two were post-operative AVN leading to femoral head collapse, 8 months and 7 years after their respective operations; and two were deep infections both 5 years after operation). Kaplan-Meier survival analysis showed a 96% cumulative survival at 9 years (figure). There were no failures from osteolysis or aseptic loosening and no patient is awaiting a revision for any reason.

Discussion: The performance of the BHR continues to be good at 9 years. Arthroplasty devices are known to manifest two phases of failure, one in the early years and another in the later years. Early failure with this device has been very low. The interim years are continuing to be promising and we are yet to find out when the late failures, if any, are likely to occur.

Introduction: The results of Birmingham Hip Resurfacing (BHR) device in several series reveal that the predominant mode of failure is femoral neck fracture or femoral head collapse and that careful patient selection and precise operative technique are vital to the success of this procedure. In this report we consider the results of BHR in patients with severe arthritis secondary to femoral head AVN.

Methods: This is a single-surgeon consecutive series of BHRs with a minimum follow-up of 5 years. Fifty six patients with Ficat-Arlet grade III or IV femoral head AVN and treated with BHRs at a mean age of 44.2 years (range 19 to 67.7 years) were followed-up for 5 to 9.2 years (mean 6.8 years). No patient died and none was lost to follow-up. Revision for any reason was the end-point and unrevised patients were assessed with Oxford hip scores. They were also reviewed clinically and with AP and lateral radiographs.

Results: There were four failures in this cohort giving a failure rate of 7% and a cumulative survivorship of 92.9% at 9 years (figure). In one further patient the femoral component has tilted into varus from further collapse of the femoral head. He is asymptomatic but knows that he will need a revision if he develops symptoms. No other patient shows clinical or radiological adverse signs.

Discussion: Several studies have shown that the results of arthroplasty are generally worse in AVN as compared to those in osteoarthritis. Reviewing the above results it appears to us that the relatively poorer cumulative survival observed in patients with a diagnosis of AVN (92.9%) compared to those with other diagnoses make AVN a relative contraindication to this procedure.

Introduction: source of elevated metal levels in patients with MM bearings continues to be debated. Under the controlled conditions of hip simulators most wear occurs within the first million cycles and subsequent motion produces negligible wear. However, in metal ion studies in patients, although there is a peak in metal levels in the early months after implantation, they never return to normal levels thereafter. In order to explain these conflicting observations it has been suggested that in vivo metal wear also occurs only during the early months and that continued corrosion of metal particles released during that period is responsible for metal level elevation later on.

If run-in wear is the only source of sustained metal release, then replacing the bearing with a non-MM bearing should not make a difference to metal release in patients and elevated levels should continue to persist even after such a revision. In order to verify this we studied metal release in patients who underwent revision of a MM bearing to a non-MM bearing after revision.

Methods. Using high resolution mass spectrometry, whole blood concentrations and daily output of cobalt and chromium were studied in four patients prospectively, whose hip resurfacings were revised to metal– polythylene THRs. None of the patients had other metal devices or compromised renal function.

Results. Preoperative levels in these patients were highly elevated as expected from a failing device. Thereafter there is a clear and progressively rapid trend of reducing metal levels in whole blood and urine.

Discussion The progressive and steep reduction of metal release following MM bearing removal suggests that corrosion from previously worn particles alone cannot account for the persistent elevation of systemic metal levels in patients with MM bearings and that bearing wear continues to occur after the initial run-in period

The dysplasia cup, which was devised as an adjunct to the Birmingham Hip Resurfacing system, has a hydroxyapatite-coated porous surface and two supplementary neutralisation screws to provide stable primary fixation, permit early weight-bearing, and allow incorporation of morcellised autograft without the need for structural bone grafting.

A total of 110 consecutive dysplasia resurfacing arthroplasties in 103 patients (55 men and 48 women) performed between 1997 and 2000 was reviewed with a minimum follow-up of six years. The mean age at operation was 47.2 years (21 to 62) and 104 hips (94%) were Crowe grade II or III.

During the mean follow-up of 7.8 years (6 to 9.6), three hips (2.7%) were converted to a total hip replacement at a mean of 3.9 years (2 months to 8.1 years), giving a cumulative survival of 95.2% at nine years (95% confidence interval 89 to 100). The revisions were due to a fracture of the femoral neck, a collapse of the femoral head and a deep infection. There was no aseptic loosening or osteolysis of the acetabular component associated with either of the revisions performed for failure of the femoral component. No patient is awaiting a revision.

The median Oxford hip score in 98 patients with surviving hips at the final review was 13 and the 10th and the 90th percentiles were 12 and 23, respectively.

We report a retrospective review of the incidence of venous thromboembolism in 463 consecutive patients who underwent primary total hip arthroplasty (487 procedures). Treatment included both total hip replacement and hip resurfacing, and the patients were managed without anticoagulants. The thromboprophylaxis regimen included an antiplatelet agent, generally aspirin, hypotensive epidural anaesthesia, elastic compression stockings and early mobilisation. In 258 of these procedures (244 patients) performed in 2005 (cohort A) mechanical compression devices were not used, whereas in 229 (219 patients) performed during 2006 (cohort B) bilateral intermittent pneumatic calf compression was used.

All operations were performed through a posterior mini-incision approach. Patients who required anticoagulation for pre-existing medical problems and those undergoing revision arthroplasty were excluded. Doppler ultrasonographic screening for deep-vein thrombosis was performed in all patients between the fourth and sixth post-operative days. All patients were reviewed at a follow-up clinic six to ten weeks after the operation. In addition, reponse to a questionnaire was obtained at the end of 12 weeks post-operatively.

No symptomatic calf or above-knee deep-vein thrombosis or pulmonary embolism occurred. In 25 patients in cohort A (10.2%) and in ten patients in cohort B (4.6%) asymptomatic calf deep-vein thromboses were detected ultrasonographically. This difference was statistically significant (p = 0.03). The regimen followed by cohort B offers the prospect of a low incidence of venous thromboembolism without subjecting patients to the higher risk of bleeding associated with anticoagulant use.

The early designs of hip resurfacing implants suffered high rates of early failure, making it impossible to obtain valuable mid-term radiostereophotogrammetric (RSA) results. The metal-on-metal Birmingham Hip Resurfacing arthroplasty has shown promising mid-term results and we present here the first mid-term RSA analysis of a hip resurfacing implant.

The analysis was performed in 19 hips at five years post-operatively. The mean acetabular component translation and rotation, and femoral component translation were compared with the previous RSA measurements at two and six months, and one and two years.

There was no statistical significance (t-test, p ≤ 0.05) between these consecutive movements, indicating the mid-term stability of the implant.

Metal ions generated from joint replacements are a cause for concern. There is no consensus on the best surrogate measure of metal ion exposure. This study investigates whether serum and whole blood concentrations can be used interchangeably to report results of cobalt and chromium ion concentrations.

Concentrations of serum and whole blood were analysed in 262 concurrent specimens using high resolution inductively-coupled plasma mass-spectrometry. The agreement was assessed with normalised scatterplots, mean difference and the Bland and Altman limits of agreement.

The wide variability seen in the normalised scatterplots, in the Bland and Altman plots and the statistically significant mean differences between serum and whole blood concentrations suggest that they cannot be used interchangeably. A bias was demonstrated for both ions in the Bland-Altman plots. Regression analysis provided a possible conversion factor of 0.71 for cobalt and 0.48 for chromium. However, even when the correction factors were applied, the limits of agreement were greater than ±67% for cobalt and greater than ±85% for chromium, suggesting that serum and whole blood cannot be used interconvertibly. This suggests that serum metal concentrations are not useful as a surrogate measure of systemic metal ion exposure.

Metal-on-metal bearings are being increasingly used in young patients. The potential adverse effects of systemic metal ion elevation are the subject of ongoing investigation. The purpose of this study was to investigate whether cobalt and chromium ions cross the placenta of pregnant women with a metal-on-metal hip resurfacing and reach the developing fetus. Whole blood levels were estimated using high-resolution inductively-coupled plasma mass spectrometry.

Our findings showed that cobalt and chromium are able to cross the placenta in the study patients with metal-on-metal hip resurfacings and in control subjects without any metal implants. In the study group the mean concentrations of cobalt and chromium in the maternal blood were 1.39 μg/l (0.55 to 2.55) and 1.28 μg/l (0.52 to 2.39), respectively. The mean umbilical cord blood concentrations of cobalt and chromium were comparatively lower, at 0.839 μg/l (0.42 to 1.75) and 0.378 μg/l (0.14 to 1.03), respectively, and this difference was significant with respect to chromium (p < 0.05).

In the control group, the mean concentrations of cobalt and chromium in the maternal blood were 0.341 μg/l (0.18 to 0.54) and 0.199 μg/l (0.12 to 0.33), and in the umbilical cord blood they were 0.336 μg/l (0.17 to 0.5) and 0.194 μg/l (0.11 to 0.56), respectively. The differences between the maternal and umbilical cord blood levels in the controls were marginal, and not statistically significant (p > 0.05). The mean cord blood level of cobalt in the study patients was significantly greater than that in the control group (p < 0.01). Although the mean umbilical cord blood chromium level was nearly twice as high in the study patients (0.378 μg/l) as in the controls (0.1934 μg/l), this difference was not statistically significant. (p > 0.05)

The transplacental transfer rate was in excess of 95% in the controls for both metals, but only 29% for chromium and 60% for cobalt in study patients, suggesting that the placenta exerts a modulatory effect on the rate of metal ion transfer.

This is a longitudinal study of the daily urinary output and the concentrations in whole blood of cobalt and chromium in patients with metal-on-metal resurfacings over a period of four years.

Twelve-hour urine collections and whole blood specimens were collected before and periodically after a Birmingham hip resurfacing in 26 patients. All ion analyses were carried out using a high-resolution inductively-coupled plasma mass spectrometer. Clinical and radiological assessment, hip function scoring and activity level assessment revealed excellent hip function.

There was a significant early increase in urinary metal output, reaching a peak at six months for cobalt and one year for chromium post-operatively. There was thereafter a steady decrease in the median urinary output of cobalt over the following three years, although the differences are not statistically significant. The mean whole blood levels of cobalt and chromium also showed a significant increase between the pre-operative and one-year post-operative periods. The blood levels then decreased to a lower level at four years, compared with the one-year levels. This late reduction was statistically significant for chromium but not for cobalt.

The effects of systemic metal ion exposure in patients with metal-on-metal resurfacing arthroplasties continue to be a matter of concern. The levels in this study provide a baseline against which the in vivo wear performance of newer bearings can be compared.