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

Introduction: Cementless cup designs in metal-on-metal (MoM) hip resurfacing devices generally depend on a good primary press-fit fixation which stabilises the components in the early post-operative period. Pressfitting the cup into the acetabulum generates non-uniform compressive stresses on the cup and consequently causes non-uniform cup deformation. That in turn may result in equatorial contact, high frictional torque and femoral head seizure. It has been reported that high frictional torque has the potential to generate micromotion between the implant and its surrounding bone and as a result adversely affect the longevity of the implant. The aim of this study was to investigate the effects of cup deformation on friction between the articulating surfaces in MoM bearings with various clearances.

Materials and methods: Six Birmingham Hip Resurfacing (BHR) devices with various clearances (80 to 306 μm) were tested in a hip friction simulator to determine the friction between the bearing surfaces. The components were tested in clotted blood which is the primary lubricant during the early post-operative period. The joints were friction tested initially in their pristine conditions and subsequently the cups were deflected by 25– 35 μm using two points pinching action before further friction tests were carried out.

Results and Discussions: It has been reported that reduced clearance results in reduced friction. However, none of the previous studies have taken cup deflection into consideration nor have they used physiologically relevant lubricant. The results presented in this study show that for the reduced clearance components, friction was significantly increased when the cups were deflected by only 30 μm. However, for the components with higher clearance the friction did not change before and after deflection. It is postulated that the larger clearances can accommodate for the amount of distortion introduced to the cups in this study.

Introduction: The increasing use of metal-metal bearings in hip arthroplasty raises concerns of elevated systemic metal levels. Lubrication theory and in-vitro studies suggest that larger diameter bearings generate less wear. Does this hold true in real life?

Methods: This is a cross-sectional study of 181 patients with either a Birmingham Hip Resurfacing or a 28mm Metasul THR. Whole blood levels (at 1year) and urinary metal ion output in the early (1 to 3) years and medium term (4 to 6years) in patients with these bearings were compared. None of the patients had other metal devices or compromised renal function. Both devices used a high-carbon cobalt-chrome bearing with no post-casting heat treatment. Cementless porous-ingrowth titanium cups and cemented polished tapered stainless steel stems or cementless porous-ingrowth titanium alloy stems were used in THRs.

Results: Whole blood metal levels at 1-year and daily output of metal ions in the early years and medium term (figure 1) in both bearings were in the same range and without a significant difference.

Discussion: Metal ion monitoring is the best way to estimate bearing wear in vivo and the best measure of device safety in the long term. Total wear over a given time period is best estimated from timed metal ion excretion rates. Blood levels represent a balance between the release of metal from the device and its renal clearance.

An earlier study (Clarke et al JBJS(Br) 2003) suggests that smaller bearings generate less wear. In that study bearings with different metallurgy and wear properties were grouped together, a potential confounding factor. The present study does not suffer from that error and our findings do not support the view that a larger bearing diameter leads to either an increase or decrease in metal ion generation.

Introduction. Painful post-collapse femoral head osteonecrosis (AVN) continues to be a therapeutic challenge. Joint preserving surgery does not produce satisfactory results after femoral head collapse, making an arthroplasty almost inevitable. Does metal-metal resurfacing offer a conservative option that matches the consistent results of a stemmed THA in these patients?

Methods. 104 consecutive resurfacings (94 patients) performed for Ficat stage III/IV AVN were reviewed clinically, radiologically and with Oxford hip scores. Mean age at operation was 43.9 years. Aetiology included trauma (20%), steroids/chemotherapy (25%), alcohol abuse (8%), AVN secondary to Perthes’/SUFE (4%) and idiopathic (43%). Two types of devices were used a) McMinn Resurfacing Arthroplasty, HA-coated smooth uncemented cup and cemented femoral component and b) Birmingham Hip Resurfacing, porous HA cup and cemented femoral component.

Results. At 2 to 11.5 years (mean 7.7 years), there were seven (6.7%) failures: four from further femoral head collapse, two infections and one osteolysis, aseptic loosening. The cumulative survival at 11years is 90% (figure 1). Mean Oxford score at follow-up is 15.4. 55% participate in moderate to heavy work or participate in regular sporting activity.

Discussion. The results of any treatment modality in AVN are not as good as those in osteoarthritis. One reason is that the etiopathological factors that caused non-traumatic AVN (steroids etc) have the potential to cause continued femoral head damage. Post-traumatic patients need complex reconstructions and risk a higher failure rate. Those on immunosuppressants are prone to infections. The results of hip resurfacing in AVN in this series are no different from THRs in many published series. Metal-metal resurfacing is a good conservative option for post-collapse femoral head AVN and gives acceptable results if strict patient selection criteria are followed.

Introduction: Dislocation rates with THA vary from 3% to 15%. One specialist centre reported a 6.4% early dislocation rate with a 28mm ceramic on polyethylene THA in young patients (mean age 56 years) in a single surgeon series. Although young patients have the advantage of better soft tissues, their greater mobility demands increase dislocation risk.

Dislocation rates in large headed metal-on-metal resurfacings are extremely low. However, many patients are unsuitable for resurfacing and need a replacement. In such cases, it is attractive to transfer the large-headed metal-metal bearing advantage to replacement arthroplasty in order to reduce wear and dislocation rates. Does large diameter metal-metal total hip replacement really reduce the early dislocation rate?

Methods: 206 consecutive primary metal-metal THRs (189 patients) were included. The device consists of an uncemented cup, a matching modular cobalt chrome head (head diameter ranged 38 – 58mm) fixed on a stem through a 12/14 cone. Cemented stems were used in 107 procedures and 99 were proximal-porous uncemented stems.

Age at operation ranged from 37 to 83 years. Thirty patients were 55 years or under, eighty one were 56 – 65 years and ninety five were over 65 years. There were 122 females and 67 males. Posterior approach was used in all.

Results: There were no dislocations in these 206 consecutive procedures.

Discussion: Metal-metal hips have lower dislocation rates than hips containing polyethylene (0.9% against 6.4% in a matched series). This is attributed to the suction-fit effect of metal-metal bearings. Large diameter bearings have the additional benefit of having to translate a greater jump distance before a dislocation. This dual advantage leading to extremely low dislocation rates was first noted in metal-metal resurfacings. In large headed metal-metal THRs, the head-neck ratio is even more favourable and these devices appear to eliminate early dislocation as a major complication.

Introduction: Hip resurfacing is a good conservative option for young patients with arthritis. Resurfacings risk two unique failure mechanisms that do not occur in THA, i.e. femoral neck fracture and femoral head collapse.

Old age, osteopaenia, alcohol abuse, and large cysts are risk factors for fractures. It has been suggested that performing a bilateral resurfacing puts the first side at risk of fracture from the force used in implanting the second resurfacing. Is this a true risk or a sampling error?

Methods: Out of 2576 consecutive resurfacings performed by the senior author (July 1997 – May 2005), 191 patients (382 hips, 14.8% of all resurfacings) presented with bilateral arthritis and had both hips operated in the same hospital admission. 133 patients had the two operations a week apart and 58 had both the same day. A posterior approach was used in all cases with the patient in the lateral position on the contralateral side.

Results: Of the 382 resurfacings, only two failed from a femoral neck fracture. Both had the second operation a week after the first. A 35-year lady (rheumatoid arthritis) sustained a femoral neck fracture of the first hip following a fall nine weeks after the operation. A 57-year man (osteoarthritis) fractured his femoral neck at 3.5 months. He fractured the side operated second.

Discussion: The incidence of femoral neck fracture in the author’s series of 2576 resurfacings is 0.4%. Patients who present with bilateral severe arthritis are more likely to have non-primary OA such as inflammatory arthritis. It is difficult to conclude if such bilateral cases are more predisposed to a fracture by virtue of the pathology itself.

The low incidence of fractures (2/382, 0.5%) in this bilateral resurfacing series does not support the view that there is an increased risk of fracture from a bilateral procedure.

Introduction: Hip resurfacing is a bone conserving option that offers a better revision prospect for young and active patients. Encouraging results from several centres prove that they function well in the early years. Their long-term survival will be known from continued monitoring of early resurfacings.

Methods: This is a retrospective study of two cohorts of young (< 55 years) patients of osteoarthritis treated with hybrid-fixed metal-metal resurfacings. The cohorts are a) consecutive patients treated by the senior author in 1994 and 95 with a hydroxyapatite-coated smooth uncemented cup and a cemented femoral component and b) consecutive patients treated with hydroxyapatite-coated porous uncemented cup and a cemented femoral component since 1997 with a minimum follow-up of 5 years. 420 resurfacings (360 patients, 287 males and 73 females) were reviewed with Oxford hip scores and activity level monitoring (UCLA scale). Mean age at operation was 48.3 years.

Results: Ten patients (11 hips) died from unrelated causes. Out of the remaining 409 hips (350 patients) at a follow-up of 5 to 11.5 years (mean 7.1 years), there was one failure (cumulative failure rate 0.25% at 11 years) from avascular necrosis of the femoral head. The mean Oxford score of the 350 patients is 13.4. 87% had a UCLA score of 7 and above. 55% participated in impact sports or were involved in heavy occupational work.

Discussion: In the present study, with no loss to follow-up, excellent hip survival (99.75%) and activity level were seen. Young patients regard return to activities as one of their highest priorities. None of these patients were advised to change their activities at work or leisure.

The extremely low failure rate in the medium term proves the suitability of resurfacing in young active patients. However, caution needs to be exercised until long term results are available.

Introduction. The usage of metal-metal bearings in young patients has rekindled the debate about the potential adverse effects of mutagenecity on offspring born to them. This question could be answered in part if it was known whether metal ions are transferred to the developing foetus. One recent study seems to suggest that such transfer does not occur [Brodner et al, J Arthroplasty2004; 19 Suppl(3) p102–107]. Unfortunately the instrument used there was not sensitive enough (5 out of 6 analyses were below the limit of detection), leaving the question of transplacental metal ion transfer unanswered. The present study uses a more powerful analytic technique.

Methods. After informed consent, whole blood specimens were obtained at the time of delivery from five patients who had undergone a Birmingham Hip Resurfacing and from their babies’ umbilical cords. High resolution plasma mass spectrometry (HRICPMS) was used for analysis.

Results. Cobalt and chromium ions have been detected in all the specimens obtained so far. The cord blood cobalt levels were lower than the mothers blood levels in all the specimens. A similar relationship was found in all but one individual chromium measurement. The mean (±95% CI) of the two groups are shown in figure 1.

Discussion and Conclusion. The present study shows that with the use of whole blood specimens rather than serum; and the use of a better analytic method than previously used in the only other study on the topic, metal ions can be detected in all specimens of patients with metal-metal devices and in the cord blood of babies born to them.

There is sufficient evidence in this study to prove that metal ions do cross the placenta. There is therefore a continuing need for vigilance on the possible effects on the offspring born to patients with metal-metal devices.

Introduction: modern cementless joints depend on bony ingrowth for durable long term fixation. Increased friction and micromotion in the early weeks can prevent ingrowth and affect long-term success.

Most friction studies are conducted in a bovine serum- carboxymethylcellulose (bs-cmc) medium. Following implantation however, the joint is bathed in blood which contains macromolecules and cells. The effect of these on friction is not fully understood.

A progressive radiolucent line (fig 1) observed in some low clearance resurfacings raises the concern that increased friction may be affecting component fixation. The purpose of this investigation was to study the effect of clearance on friction for a given bearing diameter in the presence of blood as lubricant.

Methods: Six Birmingham Hip Resurfacing devices with a nominal diameter of 50mm each and a range of diametral clearances (80, 135, 175, 200, 243 and 306μm) were used. Frictional measurements were carried out on a Prosim Hip Friction Simulator (Simsol Simulation Solutions, Stockport, UK). The test was conducted sequentially with whole blood (viscosity 0.009Pas) and a BS-CMC mixture as the lubricants (viscosity 0.01Pas).

Results: Low clearance devices (80–175μm) generated higher friction with blood than with BS-CMC (fig 2). With blood as the lubricant, low clearance devices generated much higher friction than higher clearance devices (200–306μm).

Discussion: Ongoing research into the in vitro performance of bearings is performed in hip simulators with lubricants that are believed to simulate joint fluid in terms of viscosity. However these lubricants are unable to simulate the friction effects of macromolecules.

The results of this study suggest that reduced clearance bearings have the potential to generate higher friction when blood is the lubricant. this higher friction in the low clearance bearings may produce micromotion in the early postoperative period and hamper bony ingrowth resulting in impaired fixation with long-term implications for survival.

Introduction: Metal ions generated from metal-metal joints are transported in plasma and within cells. Whole blood (WB) analysis is a good measure of systemic metal exposure because it includes both intracellular and extracellular compartments. Analysis of whole blood is technically more challenging than serum. But can serum levels be considered equivalent to whole blood levels in the assessment of systemic metal exposure?

Methods: 262 concurrent WB and serum specimens from patients after metal-metal hip arthroplasty were analyzed for metal levels by high-resolution mass-spectrometry (reporting limits 0.06μg/l for serum and 0.1μg/l for WB). The relationship between serum and WB levels were studied using four methods of agreement testing: paired t-test, Pearson correlation, Bland-Altman agreement and variability on normalized-scatter.

Results: Mean WB and serum chromium concentrations were 2.2 and 4.2μg/l (p< 0.001). Corresponding values for cobalt were 2.4 and 3.2 μg/l (p< 0.001). The normalized scatter (fig 1B) shows poor congruence between whole blood and serum levels especially at lower concentrations. Pearson correlation confirms poor agreement at lower concentrations even after excluding outliers.

Bland-Altman analysis (Figure 1A) shows the limits of agreement between serum and WB are unacceptably wide (1.7 to -5.1 for chromium) suggesting poor agreement.

Discussion: The proportion of metal ion levels in serum and blood cells shows great variability. With advances made inmass-spectrometry, poor instrument sensitivity is a non-issue. Is there then a case for continued use of serum as a measure of systemic metal ion exposure? It can be justified only if serum levels show good agreement with WB levels throughout the range of measurements. Concurrent analysis of serum and whole blood metal ion concentrations in the present study, do not show such an agreement with four methods of testing, suggesting that serum metal concentrations cannot be reliably used as an instrument to measure systemic metal ion exposure.

Hip Resurfacing has always been an attractive concept for the treatment of hip arthritis in younger patients. Introduction of modern metal-on-metal hip resurfacing in 1991 in Birmingham, UK made this concept a reality.

In the early years, resurfacings were used only by a few experienced surgeons. From 1997, Birmingham Hip Resurfacings (BHRs) are being widely used in younger and more active patients. A breakdown of the ages at operation in the regional NHS hospital in Birmingham during the period April 1999 to March 2004 show that the mean age of metal-metal resurfacings is 51 years and the mean age of total hip replacements is 70 years.

At a 3.7 to 10.8 year follow-up (mean follow-up 5.8 years), the cumulative survival rate of metal-metal resurfacing in young active patients with osteoarthritis is 99.8%. In the long term, none of these patients were constrained to change their occupational or leisure activities as a result of the procedure. The overall revision rate of BHRs in all ages and all diagnoses is also very low (19 out of 2167 [0.88%] with a maximum follow-up of 7.5 years).

Improvements in instrumentation and a minimally invasive approach developed by the senior author have made this successful device even more attractive. Although objective evidence does not support the fact that the longer approach was any more invasive than the minimal route, patient feedback shows that it is very popular with them. While minimal approach is indeed appealing, it has a steep learning curve. In the early phase of this curve, care should be taken to avoid the potential risk of suboptimal component placement which can adversely affect long-term outcome.

It is true that metal-metal bearings are associated with elevated metal ion levels. In vitro studies of BHRs show that they have a period of early run-in wear. This is not sustained in the longer term. These findings are found to hold true in vivo as well, in our studies of 24- hour cobalt output and whole blood metal ion levels. Epidemiological studies show that historic metal-metal bearings are not associated with carcinogenic effects in the long-term.

Metal ion levels in patients with BHRs are in the same range as the levels found in those with historic metal-metal total hip replacements.