Introduction

Large diameter metal-metal total hip replacements (MM THRs) offer the advantages of low wear and low dislocation risk and are being increasingly used in high-demand patients whose bone quality rules out the possibility of a hip resurfacing. However suggests that large headed MM devices may result in greater systemic metal exposure compared to small diameter bearings. This raises fresh concerns of elevated systemic metal levels.

Introduction

Secondary osteoarthritis in a dysplastic hip is a surgical challenge. Severe leg length discrepancies and torsional deformities add to the problem of inadequate bony support available for the socket. Furthermore, many of these patients are young and wish to remain active, thereby jeopardising the long-term survival of any arthroplasty device.

For such severely dysplastic hips, the Birmingham Hip Resurfacing (BHR) device provides the option of a dysplasia component, a hydroxyapatite-coated porous uncemented socket with two lugs to engage neutralisation screws for supplementary fixation into the solid bone of the ilium more medially. The gap between the superolateral surface of the socket component and the false acetabulum is filled with impacted bone graft.

Evidence with respect to conventional hip arthroplasties suggests that device wear is related to patient activity rather than duration of usage. Activity level questionnaires appear to suggest that subjects with resurfacing arthroplasties continue to remain active after the procedure. However there is a paucity of objective evidence relating to the step rates of these patients in their daily lives and its effect on metal ions generated. The aim of this investigation is to assess

the activity levels of hip resurfacing patients as follow up progresses and

Twenty-five consecutive male patients (average age 56 years) who underwent a unilateral 50 mm diameter hip resurfacing carried out by a single surgeon (DJWM) were recruited after informed consent. Patient step activity (Step Activity Monitor, SAM, Cymatech. Seattle WA, USA) was recorded at 1, 2, and 4-year follow-up stages and at the same time patient whole blood samples were collected and analysed using High Resolution Inductively Coupled Mass Spectroscopy (HR-ICPMS).

All patients in this study had well functioning hips at the four year follow up stage. All femoral components implanted were within the desired range of neutral to 10°. The mean acetabular component inclination angle was 42° (33° – 55°). Patient overall step activity remains unchanged up to the 4-year follow-up period.

At one year follow up, the whole blood cobalt and chromium concentrations show no correlation to mean number of steps taken per day by each patient (r2=0.02).

The correlation between whole blood cobalt and chromium concentration versus a function of body weight and peak index is not significant (r2=0.11).

This study provides objective evidence of the activity rates of patients at different stages of follow-up after a MoM surface replacement arthroplasty. It should be emphasised that the walking speeds of these patients on average was significantly slower than 1 Hz, which is generally used in laboratory hip simulator studies.

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.

Introduction: In vitro studies have shown that low clearance bearings have the potential to generate low wear. However, cementless acetabular cups are designed to be press fitted into the acetabulum, which could generate compressive stresses and non-uniform cup deformation during implantation. Deformation of the low clearance acetabular cups could also potentially lead to clamping or seizure of the joints and high frictional torque leading to implant failure. To obtain the benefit of low clearance and low wear, without compromising the tribological performance of the cup, a deflection compensation (DefCom) cup was designed. DefCom offers the benefits of low wear associated with low clearance components whilst reducing the risk of component seizure and high frictional torque due to component deformation.

Aim: The study was conducted in order to evaluate the tribological performance of a DefCom acetabular cup.

Materials and Methods: 50 mm diameter metal-on-metal DefCom hip resurfacing cups were used in this study. The components had an average clearance of 105±3 μm at the articulating sphere. Three of the cups were deformed plastically, along the ilial-ischeal column of the acetabulum. The degree of deformation was measured using the coordinate measuring machine, measuring the change in diameter of the cup in the direction of deformation. The cups were deformed on average by 65μm. The devices were tested in a ProSim hip wear Simulator for 5 million cycles. The lubricant was new born calf serum with 0.2% sodium azide diluted with de-ionised water to achieve protein concentration of 20 mg/ml. The flexion/extension was 30° and 15° with an internal/external rotation of ±10°. The force was Paul-type stance phase loading with a maximum load of 3 kN and a swing phase load of 0.3 kN, conducted at 1 Hz.

Results: The DefCom and deformed DefCom components showed a similar bi-phasic wear pattern to that of the BHR devices. Showing a period of ‘running in’ wear up to 1 Mc and then a reduced wear rate during the steady state phase from 1 Mc onwards. The DefCom devices produced a wear rate of 0.24 mm3/Mc, whilst the deformed DefCom joints produced a wear rate of 0.48 mm3/Mc for the running-in phase. Steady state wear was achieved for all joints after 1 Mc. The average steady state wear (1.0–5.0 Mc) rate for the DefCom joints was 0.12 mm3/Mc, with 0.14 mm3/Mc for the deformed joints joint. The wear rate for the non-deformed DefCom device is lower than that generated by the BHR, which were 0.72 mm3/Mc and 0.18 mm3/Mc for the running-in and steady state wear, respectively.

Conclusion: The study has shown that the DefCom acetabular cup has the potential to reduce the initial running-in wear by reducing the clearance at the contact area between the head and cup, whilst compensating for deformation that may occur during cup implantation.

This is the first six-year report of a prospective longitudinal study of daily output of cobalt and chromium in urine and their levels in blood following hybrid metal-on-metal surface arthroplasty.

Urine and whole blood specimens were analyzed before and periodically after hip resurfacing in 26 male patients after informed consent (mean age 52.9 years, mean BMI 27.9). Two of these patients have undergone contralateral hip resurfacings for progressive pain from end-stage arthritis and had to be excluded.

All patients were found to have well-functioning resurfacings at 6-year follow-up. No patient complained of persistent pain or disability. The median 6-year Oxford hip score was 12. Urine chromium and cobalt at six years were 3.9 and 7.8 μg/24 hrs and blood levels were 1.11 and 1.17μg/l respectively. Both urine and blood levels show a statistically significant early increase reaching a peak six months to one year postoperatively followed by a steady decrease over the following five years, although the individual reductions are not statistically significant, except for blood chromium where the 4 and 6 year levels were significantly lower than the 1-year level.

Elevated systemic metal exposure following MM bearing arthroplasty continues to cause concern. Our results show that metal release in these bearings shows a reducing trend after an initial peak dispelling the fear that a steady build-up of in vivo metal occurs with progressively increasing blood levels. However, as long as the significance of these elevated levels remains unknown, the need for continued vigilance persists.

It has been suggested that metal ion level elevations in certain bilateral MM bearing arthroplasties were overwhelming the renal threshold for metal excretion leading to systemic build-up of metal ions above the expected levels. In order to investigate this we studied renal concentrating efficacy through concurrent specimens of urine and whole blood over a range of metal levels.

Concurrent specimens from 305 unselected patients were obtained. They include preoperative patients (76) and those with unilateral and bilateral hip arthroplasties (229) through to ten years after operation. 39 pre-operative specimens and 4 follow-up specimens had blood levels at or below the detection limit for cobalt or chromium and were excluded. The ratio of urine to whole blood concentration was 0.78 in the pre-operative patients. In patients with MM arthroplasties the different ratios in patients increased (from 3.1 to 9.2) with increasing urine concentrations.

The ratio of urine cobalt concentration to blood cobalt concentration is a measure of renal concentrating efficacy. Amongst pre-operative controls, this ratio is 0.78, indicating that there is renal conservation of cobalt. In terms of cobalt, these patients’ urine was dilute in comparison to whole blood. In patients with MM bearings, the ratio went up to 4.8 indicating that the kidneys were now actively excreting against a concentration gradient in an attempt to maintain internal milieu. If renal threshold was being breached at higher levels, then the ratio should progressively fall at higher concentrations. The trend in this experiment shows quite the contrary effect and the ratio reached 9.2 in those with urine cobalt > 15 μg/l, demonstrating that renal clearance efficiency holds up even against this steep gradient and that the threshold is not breached within clinically relevant levels.

Introduction: Metal-metal (MM) surface replacement arthroplasty of the hip is showing promise as an effective and enduring solution in the management of hip arthritis in the young, and is being increasingly used. The main concern is the release of metal ions into the systemic circulation and their long-term effects. There is concern that metal ions cross the placenta in pregnant women with MM bearing arthroplasties with the potential for mutagenic effects in the offspring. The hypothesis is that metal ions pass freely through the placenta and that there is no difference in the maternal and cord metal ion levels.

Methods: This is a controlled cross-sectional study of women of child-bearing age with MM bearing surface replacement arthroplasties. (n= 25, mean age: 32 years, mean duration after resurfacing 60.3 months, 3 bilateral). The control group consisted of 24 subjects who do not have a metallic implant, were not taking any supplements containing cobalt or chromium salts and were registered to undergo an elective LSCS at the regional hospital. Mean age of the control group was 31.3 years. No patient in either group was known to have renal failure. Whole blood specimens were obtained from the mothers just before delivery and before infusion of any fluids, and cord blood specimens were obtained immediately after delivery. High resolution inductively couples mass spectrometry (HRICPMS) was used for metal ion analysis.

Results: Cobalt and chromium were detectable in all specimens in both the study patients and controls. In the study group, mean cord metal ion levels were significantly lower than the maternal cobalt (p < 0.05) and chromium (p < 0.0001) levels thus rejecting the null hypothesis. In the control group, the mean difference between maternal and cord metal ion levels was only 5 to 7% and was statistically not significant (p > 0.5).

The mean difference in cord chromium between the study and control groups is not statistically significant (p > 0.05), although cord cobalt in the study group is significantly higher (p < 0.01) than that in controls. Whilst there is a four-fold elevation of maternal cobalt in the study patients and an almost 7-fold increase in maternal chromium levels as compared to the control group, the elevation in the cord cobalt and chromium in the study group are smaller.

Discussion and Conclusion: The differences between maternal and cord metal ions in the control patients indicate that normally the placenta allows an almost free passage of metal ions. This is understandable when we realize that these elements are also required by the developing foetus for its cellular and metabolic functions. The relative levels of metal ions in the maternal and cord blood in the study group patients reveal that the placenta does exert a modulatory effect on metal transfer. The mean cord levels of cobalt and chromium in these patients are only 57% and 24% of the maternal blood levels respectively. There is a continuing need for efforts to reduce metal ion release from artificial joints and also to monitor metal ion levels in patients with MM devices.

Introduction: The accepted method of assessing wear following a hip simulator test has been to use a precision balance. As the MoM devices produce significantly less weight loss than hard-on-soft bearings, the measurements of MoM devices are now almost at the detection limit of many balances. There is a need for a method that can be used in conjunction with gravimetric analysis that will provide an accurate assessment of ion concentration levels that will support the gravimetric measurements.

Aim: To develop a method to assess wear using metal ion analysis in order to support gravimetric measurements of metal on metal devices.

Materials and methods: Hip simulator test: Three pairs of 50 mm diameter as cast CoCr MoM devices were tested in a ProSim hip wear simulator (SimSol Stockport/UK) under physiologically relevant conditions. The lubricant was new born calf serum with 0.2 % sodium azide concentration diluted with de-ionised water for protein concentration of 20 g/l. Stop-start motion was implemented every 100 cycles. Lubricant changed every 125 k cycles. The frequency was 0.5 Hz. Wear was assessed gravimetrically at every 0.5 million cycles (Mc) interval.

Ion analysis: Serum was collected from test station and allowed to settle for 12 hours. An aliquot of 20 ml from lubricant was collected. Each sample was centrifuged at 2500 g-force for 10 minutes. A 10 ml aliquot was collected from each sample and was further centrifuged at 2500 g-force for 10 minutes. 1.5 ml aliquot was collected and stored at −20 °C. A high resolution inductively-coupled plasma mass spectrometry instrument (ELEMENT, ThermoFinnigan MAT, Bremen/Germany) was then used for the analysis of metal ions.

Results and Discussion: The average cumulative metal ion levels at 0.5, 1 and 1.5 Mc showed similar trends in wear to that of the average cumulative weight loss assessed gravimetrically. There were similar biphasic wear trends in both metal ion levels and gravimetric weight losses. Other studies have also shown similar correlation between volume loss and ion concentration levels. The percentage distribution of Co, Cr and Mo in the metal ion samples are in close agreement with nominal chemical composition of the material tested.

Conclusion: This study showed that metal ion measurements can help to confirm gravimetrically measured material loss.

Introduction: Metal-on-metal (MM) bearing wear releases soluble metal ions which enter the systemic circulation and insoluble metal particles which collect in the periprosthetic tissues and disseminate through the lymphoreticular system. Disseminated particles also release ions through corrosion. The rate of metal ion level reduction following revision of a MM bearing offers insights into the relative contribution of metal ions from the bearing and from disseminated particles.

Methods: Whole blood concentrations and daily output of metal ions were studied, prospectively over a period of one year, in seven patients whose MM 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 trend of reducing metal levels in whole blood and urine in a biphasic manner. Over the first four weeks there is a rapid decline, followed by a period of slow decrease over the next twelve months (figure).

Discussion: The steep reduction of cobalt release immediately following revision supports the reported short half-life of cobalt ions. The later protracted trend can only be accounted for through progressive corrosion from previously worn particles. However this trend is also not sustained indefinitely and tends to approach control levels eventually.

Some authors have suggested that metal wear in patients with well-functioning MM bearings occurs only during the run-in wear phase and that continued corrosion of metal particles released during that period is responsible for metal level elevation later on. However the reducing trend in the later phase following revision in this study suggests that metal ion elevation from corrosion is not sustained indefinitely and therefore cannot by itself account for the persistent elevation of systemic metal levels throughout. Bearing wear continues to occur throughout bearing life.

Introduction: End-stage hip arthritis secondary to femoral head avascular necrosis (AVN) in young patients is a therapeutic challenge. Hip resurfacing (HR) has been showing excellent medium-term results in patients with osteoarthritis. Destructive changes in a large segment of the femoral head from AVN can increase the risk of postoperative femoral neck fracture or femoral head collapse following a resurfacing procedure. Careful patient selection and precise operative technique are vital to success. This is a study of the results of HR in patients with arthritis secondary to femoral head osteonecrosis.

Methods: This is a single-surgeon consecutive series with a 4 to 14-year (mean 8.6) follow-up. 95 patients (104 hips) with Ficat-Arlet grade III or IV osteonecrosis and treated with HR at a mean age of 43 (range 18 to 68) years. Two patients died due to unrelated causes and none is lost to follow-up. Revision for any reason was the end-point. Unrevised patients were assessed clinically and with Oxford hip scores and AP and lateral radiographs.

Results: Nine failures (1 fracture, 5 femoral head collapse, 2 infections, 1 cup loosening) give a failure rate of 8.7% and a cumulative survivorship of 89% at 14 years. In one further patient the femoral component has tilted into varus. He is asymptomatic but knows that he may need a revision if symptoms develop. No other patient shows clinical or radiological adverse signs.

Discussion and Conclusion: Several studies suggest that the results of arthroplasty are generally worse in AVN compared to those in osteoarthritis. HR has demosntrated good results in young patients with good quality femoral head bone. Reviewing the above results it appears to us that the relatively poorer cumulative survival observed in patients with a diagnosis of AVN (89%) makes AVN a relative contraindication to hip resurfacing.

Introduction: Metal-metal (MM) hip resurfacing is being increasingly used in the young. The main concern is the invariable systemic metal ion release. In young women the concern is that metal ions cross the placenta in pregnant women with MM bearing arthroplasties. We earlier presented an interim report on this subject the results of which ate established in a larger cohort

Methods: This is a controlled cross-sectional study of women of child-bearing age with MM resurfacings. (n= 22, mean age: 32 years, mean duration after resurfacing 60.3 months, 3 bilateral). The control group consisted of 24 pregnant subjects who did not have a metallic implant (mean age 31.3 years). Whole blood specimens were obtained from the mothers and umbilical cords at delivery.

Results: None of the babies had a congenital anomaly. Cobalt and chromium were detectable in all specimens including all controls. In the study group, mean cord metal ion levels were significantly lower than the maternal cobalt (p < 0.05) and chromium (p < 0.0001). In the control group, the mean cord blood metal levels differed very little from the maternal levels (p > 0.5). The mean difference in cord chromium between the study (0.33 μg/l) and control groups (0.21 μg/l) was not statistically significant, although the difference in cord cobalt was significant (0.41 μg/l).

Discussion: The differences between maternal and cord metal ions in the control patients is very small indicating that, under these circumstances the placenta allows an almost free passage of metal ions. The relative levels in the study group reveal that the placenta exerts a modulatory effect on metal transfer when maternal levels are above normal. Cobalt and chromium cross the placenta, irrespective of the presence of metal devices and therefore there is a need to continue efforts to reduce metal ion release.

Introduction: To develop a more physiologically relevant hip simulator test protocol and study the effect of microstructure on the wear performance of as-cast (AC) and double heat treated (DHT) devices under the new protocol.

Methods: Three pairs of AC and four pairs of DHT 50 mm CoCr metal-on-metal (MoM) devices were tested. The lubricant used was bovine serum. Stop-start motion was implemented between the two sets of kinetics and kinematics that alternated every 100 cycles throughout the test. Condition one: The flexion/extension was 30° and 15° respectively. The internal/external rotation was ±10°. The force was Paul type stance phase loading with a maximum load of 3 kN and a standard ISO swing phase load of 0.3 kN. Condition two: The flexion/extension was ±22°. The internal/external rotation was ±8°. The force was a maximum stance phase load of 2.2 kN and a swing phase load of 0.24 kN at 0.5 Hz frequency. Wear was assessed gravimetrically.

Result: The masking effect of 1 Hz speed and uninter-rupted motion, in providing exaggerated lubrication regime, was exposed under more physiologically relevant test conditions. The AC devices have significantly reduced wear when compared to the DHT devices. It can also be seen that from 0.5 to 2 Mc the divergence in wear has increased.

Conclusion: A more physiologically relevant hip simulator test protocol was successfully developed and implemented, in showing the effect of microstructure on wear as seen in vivo, where high wear of DHT devices has been observed. 295

Introduction: Systemic metal ion elevation continues to cause concern with metal-on-metal (MM) bearings, particularly in young people, in view of their expected long life-time usage. Reducing bearing clearance is claimed to be a means of reducing metal ion release.

Methods: 26 consecutive male patients (mean age 55 years, mean BMI 26) who fulfilled the inclusion criteria and received a 50mm bearing (diametral clearance 100 μm) were included. Clinico-radiographic review and urine and blood specimens were obtained before and periodically after the procedure. Two hips were excluded during follow-up, (one revision and another contralateral hip arthroplasty). Results were compared with a similar design bearing, 50 or 54 mm diameter and conventional clearance.

Results: At the four-year stage all patients had excellent hip function. However three patients had progressive acetabular radiolucent lines. Cobalt and chromium in both cohorts at all follow-up levels were significantly higher than the preoperative levels. Compared to the conventional clearance (CC) group, the pre-operative urine chromium and 6M to 48M urine cobalt and chromium were significantly lower in the LC group (p < 0.005). Blood metal levels were lower in the LC group at 1-year follow-up but showed a converging trend thereafter. At 4-year follow-up, the differences are considerably less, with no significant difference in blood cobalt (figure).

Discussion: Under ideal conditions, closely matched components (lower clearance) would lead to a thicker fluid film and less wear. However a larger clearance than ideal is needed to allow for asphericities, surface roughness, deformation and the evolution of in vivo lubricant. Peri-acetabular radiolucent lines cause concern. Attempts to reduce systemic metal exposure should not adversely affect other bearing characteristics such as friction. The search for a bearing which would generate low wear without producing a detrimental effect on other bearing attributes, such as friction, should continue.

Introduction: In vitro simulation experiments and in vivo metal ion studies have been used to investigate metal-metal bearing wear. In vitro studies demonstrate an early high wear phase followed by a rapid decline to a significantly lower steady state phase. Clinical metal ion studies have never shown such a significant fall in later years although they reveal early high wear. This study compares in vitro and in vivo wear rates.

Methods: In vivo measurements were obtained from daily cobalt excretion in 26 patients with 50 and 54mm resurfacings up to 4 years. Their activity averaged 2Mcyc-per-yr. In vitro measurements were obtained from gravimetric wear rates (Prosim hip simulator) of ten 50 mm diameter resurfacings of the same design. Diluted calf serum was the lubricant.

Results: Simulator results, shown in fig 1, are wear per day equivalent. In fig 2 it is seen that during the first year simulator results predict wear that exceeds metal ion output. This can be accounted for by postulating that particulate debris is higher during the early years. Subsequently the plots converge showing that particulate debris release is progressively reduced in comparison to metal ion release. At 3 years the simulator predicts lower wear than that observed in the metal ion study. This can be accounted for by postulating that corrosion of previously shed particles is responsible for the difference.

Discussion: From these results it can be stated that during the run-in period, 4/5ths of bearing wear occurs as insoluble particles and the rest is soluble metal ions. This relationship progressively changes through the steady state phase. At around the 3-year stage, even if we assume that most bearing wear releases soluble metal ions, nearly a fifth (2.8/14.4) can only be accounted for through passive corrosion of wear particles.

Introduction: Modern metal-metal (MM) Hip Resurfacing (HR) was developed as a conservative option for young patients with severe arthritis. Whilst some centres have reported excellent early results, other series have found a high incidence of osteolysis and still others reported soft tissue necrosis and periarticular changes. These are not always detectable with conventional imaging. This is the first 10 year clinico-radiological and multi-slice CT assessment of hip resurfacings.

Methods: The study includes 124 consecutive single-surgeon HRs (113 patients), mean age 52.8 years (27 to 75), mean follow-up 10.6 (10.4 to 10.8 years). Diagnoses include primary osteoarthritis (102), osteonecrosis (6), dysplasia (12) and others (4). Five patients (7 hips) died 5 to 10.3 years later from unrelated causes. Unrevised patients are reviewed with questionnaires, conventional radiographs and CT assessment.

Results: With revision for any reason as the end-point there were seven failures 0.4 to 9.7 years after operation (one failed from femoral neck fracture, four due to femoral head collapse and two were deep infections, 94% 10-year cumulative survival. Five cases showed osteolysis and four had neck thinning. No aseptic loosening, migration or malorientation is found. No patient is awaiting a revision.

Discussion and Conclusion: The performance of MMHR continues to be good at 10 years. Arthroplasty devices are known to manifest two phases of failure, one during early years and another in later years. Early failure with this device has been low. The interim years continue to be promising and we are yet to find out when the late failures are likely to occur.

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.