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.

Blood metal ion sampling can help detect poorly functioning metal-on-metal hip arthroplasties (MoMHA's) requiring revision. Little is known about the variation in these levels following bearing exchange. This study aimed to determine the changes that occur in blood and urine metal ion concentrations following MoMHA revision.

A single-centre prospective cohort study was undertaken between 2005 and 2012 of patients with failing large-diameter MoMHA's and high blood metal ions requiring revision to non-metal-on-metal articulations. All patients had normal renal function. Whole blood and urine were collected for metal ion analysis preoperatively and regularly following revision.

Twenty-three MoMHAs (21 hip resurfacings and 2 total hip arthroplasties; mean age 56.0 years and 65% female) were revised at a mean time of 7.9 years (range 2.0–14.5 years) from primary surgery. All revisions were performed by the senior author using primary total hip implants (12 ceramic-on-polyethylene bearings, 10 oxinium-on-polyethylene bearings, and 1 metal-on-polyethylene bearing implanted). Mean (range) metal ion concentrations pre-revision were: blood cobalt 13.9µg/l (1.32–74.7µg/l), blood chromium 8.9µg/l (1.29–57.3µg/l), urine cobalt 104.6µg/24 hours (4.35–747.3µg/24 hours), urine chromium 33.2µg/24 hours (4.39–235.4µg/24 hours). After revision the mean metal ion concentrations (percentage of pre-revision values) were: blood cobalt at 2 days=10.7µg/l (77%), 6 days=7.7µg/l (55%), 2 months=3.4µg/l (24%), 1 year=1.0µg/l (7%), 2 years=0.42µg/l (3%); blood chromium at 2 days=8.7µg/l (98%), 6 days=5.5µg/l (62%), 2 months=2.2µg/l (25%), 1 year=1.5µg/l (16%), 2 years=0.97µg/l (11%); urine cobalt at 2 days=31.9µg/24 hours (30%), 6 days=21.5µg/24 hours (21%), 2 months=6.1µg/24 hours (6%), 1 year=0.99µg/24 hours (1%), 2 years=0.61µg/24 hours (1%); urine chromium at 2 days=34.4µg/24 hours (103%), 6 days=15.8µg/24 hours (48%), 2 months=9.3µg/24 hours (28%), 1 year=2.8µg/24 hours (8%), 2 years=1.9µg/24 hours (6%).

Following MoM revision cobalt levels decline rapidly in an exponential pattern with a single rate of decay through the 2 year period, reaching reference levels within the first year. Chromium follows a similar pattern but starts lower and takes longer. Renal response to cobalt returns to reference level within days of revision.

The use of modular systems adds versatility to the implant system, better restoration of hip biomechanics and lower inventory to the hospital. There have been reports of high metal ions, ARMD reactions and high implant failure rates due to potential problems from taper failures. These are more common in metal-on-metal hip replacements, but are being also reported in other bearings.

Between 2001 and 2010, we performed 383 consecutive metal-on-metal (MoM) THRs through a posterior approach, using a BHR cup and Birmingham modular head with one of three different stems, all with 12/14 tapers. The earliest 104 hips employed a cemented MS30 stem (Zimmer GmbH, Winterthur, Switzerland). Subsequent 256 were Synergy and then 23 Anthology (both uncemented and both Smith and Nephew Orthopaedics, Memphis TN USA). There was no significant difference in the average age at surgery (65.4 years cemented vs 65.6 uncemented, p = 0.69), gender ratio (1.68 vs 1.89, p = 0.64), or bearing diameter (46.7 vs 46.8, p = 0.31). The earlier 203 Synergy stems were monoblock heads, while the remaining uncemented stems included a tapered sleeve in addition.

There were 3 deep infections and 11 debris-related failures (overall revision rate 4.9%). The revision rate from aseptic failures (ALTR, effusion, osteolysis or component loosening) is 2.87%. Kaplan-Meier analysis of the entire cohort showed a 10-year implant survival of 96.8% with revision for any reason as the end-point. Cemented stems had a 100% survival at 10 years and 98.6% at 12 years. The uncemented stems had a 93.8% survival at 10 years. Within the uncemented group, the monoblocks had a 5 and 10-year survival of 99.0% and 96.4% respectively while the sleeved had 98.7% (5 years) and 96.3% (7 years) and 82.5% at 8 years. Retreival analysis showed clear evidence of taper failure.

Our experience suggests taper failure leading to ALTRs and its sequelae. Others have reported ALTR type reactions in metal on polyethylene and ceramic on polyethylene bearing types as well in bearing diameters ranging from 28mm to 40mm. There is a need to improve taper design especially for use with large heads, and in high demand patients.

The natural knee allows multi-planar freedoms of rotation and translation, while retaining stability in the antero-posterior direction. It allows flexion with roll back, and medial, lateral and central rotation movements. The natural femoral condyles of the knee are spiral, therefore inducing a side to side translatory movement during flexion and extension. Incorporating all these features is vital in successful knee replacement design.

The different knee designs currently in use demonstrate different deficiencies in knee function. A study of 150 Posterior Cruciate (PCL) Retaining Total Knee Replacements [1] has shown that in 72% of knees direct impingement of the tibial insert posteriorly against the back of the femur was responsible for blocking further flexion. The mean pre-operative range of flexion was 105° and post-operative was 105.9°. For every 2mm decrease in posterior condylar offset, the maximum flexion was reduced by 12.2°.

The major disadvantage of the Posterior Stabilised (PS) Total Knee Replacement is gross anterior to posterior mid-flexion instability [2]. The Medial Rotation Total Knee Replacement is good in mid-flexion but not in high flexion where the femur slides forward on the tibia leading to impingement.

The Birmingham Knee Replacement (BKR) is a rotating platform knee design which is stable throughout the range of flexion. In high flexion, the BKR brings the femur to the back of the tibia. The BKR also has spiral femoral condyles, matching the natural kinematics of the knee. The combined static and dynamic effect is 10mm lateral translation of the femur in flexion and vice versa in extension.

Results for seventy nine BKRs (in seventy two patients) show the best Oxford Knee Score of 12 at follow up – excluding ten patients whose inferior scores were due to other pathologies. Knee flexion results show a 21° post-operative improvement in range of flexion.

On objective independent testing, maximum walking speed is slower for patients with a standard knee replacement (6.5km/h) and the loading through the replaced side does not match the normal side. Comparatively, patients with a BKR have a faster maximum walking speed of 11km/h and the loading closely matches that of the normal knee.

Studies based on the National Joint Register PROMs data [2] show that nearly thirty percent of Total Knee Replacement patients are not much better since their operation. A lot of improvement is needed in the design of knee replacements in order to achieve better function for knee replacement patients.

Objectives

To examine mortality and revision rates among patients with osteoarthritis undergoing hip arthroplasty and to compare these rates between patients undergoing cemented or uncemented procedures and to compare outcomes between men undergoing stemmed total hip replacements and Birmingham hip resurfacing.

High short-term failure rates have been observed with a number of metal-on-metal (MoM) hip designs. Most patients require follow-up with blood metal ions, whichprovide a surrogate marker of in-vivo bearing wear. Given these results are used in clinical decision making it is important values obtained within and between laboratories are reproducible.

To assess the intra-laboratory and inter-laboratory variability of blood metal ion concentrations analysed by four accredited laboratories.

Whole blood was taken from two participants in this prospective study. The study specimen was obtained from a 42 year-old female with ceramic-on-ceramic hip arthroplasty failure resulting in unintended metal-on-ceramic wear and excessively high systemic metal ion levels. The control specimen was from a 52 year-old healthy male with no metal exposure. The two specimens were serially diluted to produce a total of 25 samples with different metal ion concentrations in two different anticoagulants each. Thus 50 samples were sent blinded in duplicate (total 100) to four accredited laboratories (A, B, C, D) to independently analyse blood metal ion concentrations. Ten commercially available reference specimens spiked with different amounts of metal ions were also obtained with known blood metal ion concentrations (range for cobalt 0.15µg/l-11.30µg/l and chromium 0.80µg/l to 37.00µg/l) and analysed by the four laboratories.

The intra-laboratory coefficients of variation for repeat analysis of identical patient specimens were 7.32% (laboratory A), 4.64% (B), 7.50% (C), and 20.0% (D). The inter-laboratory variability for the analysis of all 25 samples was substantial. For the unmixed study specimen the laboratory results ranged from a cobalt of 263.7µg/l (D) to 525.1µg/l (D) and a chromium of 13.3µg/l (D) to 36.9µg/l (A). For the unmixed control specimen the laboratory results ranged from a cobalt of 0.13µg/l (B) to 0.77µg/l (D) and a chromium of 0.13µg/l (D) to 7.1µg/l (A). For one of the mixed specimens the laboratory results ranged from a cobalt of 12.50µg/l (A) to 20.47µg/l (D) and a chromium of 0.73µg/l (D) to 5.60µg/l (A). Similar inter-laboratory variation was observed for the other mixed samples. The true mean (standard deviation) of the 10 commercial samples was 4.48µg/l (4.20) for cobalt and 8.97µg/l (10.98) for chromium. This was similar to the values obtained by all four laboratories: mean (standard deviation) cobalt ranged from 3.54µg/l (3.17) in laboratory A to 4.35µg/l (4.13) in laboratory D, and chromium ranged from 7.76µg/l (9.50) in laboratory B to 9.55µg/l (9.16) in laboratory A.

When testing patient samples, large variations existed both between and within four laboratories accredited to perform analysis of blood metal ion concentrations. However, this was not the case when assessing commercially spiked samples which are regularly used to validate laboratory testing. This is of great clinical concern and could lead clinicians to either recommend unnecessary revision or delay surgery, with both having the potential to adversely affect patient outcomes. It is recommended that laboratories use patient samples to assess the accuracy and reproducibility of the analyses performed. This may also assist in explaining the variations observed in this study.

Metal-metal surface replacement (MoMSRA) is increasingly used in the young. Systemic metal ion release and its effects cause concern. Do metal ions cross the placenta in pregnant women with potential mutagenic effects? The hypothesis is that metal ions pass freely through the placenta and there is no difference in maternal and cord metal levels.

This is a controlled cross-sectional study of women with MoMSRA. (n=25, mean age 32years, implantation 60months, 3 bilateral). The control group were 24 subjects with no metallic implant and not receiving cobalt/chromium supplements, mean age 31years. No patient was known to have renal failure. Whole blood specimens were obtained before delivery/ fluid-infusion and Cord blood specimens immediately after delivery.

Cobalt and chromium were detectable in all specimens in both cohorts. In the control group, the difference between maternal and cord levels was only 5 to 7% indicating free passage. Study group cord levels were significantly lower than maternal cobalt, p<0.05 and chromium p<0.0001 thus rejecting the null hypothesis.

The differences between maternal and cord metal ions in the controls indicate that normally the placenta allows an almost free passage of metal ions. The relative levels of metal ions in the maternal and cord blood in the study group reveal that the placenta exerts a modulatory effect on metal transfer.

Kinematics of the knee change during the full range of flexion [1]. The lateral femoral condyle (LFC) rolls back progressively through the entire range of flexion. The medial femoral condyle (MFC) does not move back during the first 110 degrees, but from 110 to 160 degrees it moves back by 10mm. This dual arc makes anatomical knee design a challenging task. In medial rotation, during flexion, the MFC stays in place, but the LFC moves forward in extension and backward in flexion. In lateral rotation the LFC stays still while the MFC moves back and forward in flexion and extension. During central rotation both condyles move reciprocally. However the knee is stable against an anteriorly or posteriorly directed force. It is important that all these degrees of freedom and stability are reproduced in total knee replacement (TKR) design.

Furthermore, the two femoral condyles together form a spiral. Like the threads of a screw in a nut they allow medio-lateral translation of the femur [2] in the tibial reference frame. During flexion the knee centre moves laterally nearly 20% of the width of the tibial plateau and in extension the femur translates medially. This medio-lateral translation occurs in the natural normal knee joint. This has special significance in knee design because the natural femur (along with the trochlea) moves laterally in flexion, allowing the patella to be sited laterally, while most regular TKRs drive the patella medially. In order to test this anomaly we studied patellar maltracking in vivo and in cadavers.

In vivo tracking studies using a patellar tracker during total knee replacement demonstrated average patellar maltracking of 10mm with regular TKR designs. Experiments on 22 cadaveric limbs using loaded quadriceps mechanism and trackers on the femur, tibia and patella, showed that in the natural knee the patella tracked medially by an average of 5mm. In regular TKRs the patella tracked medially. Compared to a normal knee, the patella in these designs maltracked on average by 10mm. Spiral condyles applied to the same bone cuts in the cadavers allowed the patella tracking to return to the expected lateral position in flexion.

This has application to total knee replacement design. Unless the spiral design is incorporated in the condyles, patellar maltracking is inevitable and is likely to cause lateral knee pain and stiffness post-operatively.

The modern era of hip resurfacing was initiated over two decades ago to address the poor results of existing hip replacement devices in young patients. High failure rates have been reported with certain resurfacings. This is a 1 to 17-year review of a single surgeon series of resurfacings in patients under the age of 50 years.

Between July 1997 and June 2014, 3627 hip resurfacing arthroplasties were implanted at our Centre in 2878 patients using a posterior approach. Of these 863 patients (1063 hips, 754 in men and 309 in women) were under the age of 50 years at the time of operation. They were followed up with postal questionnaires for up to 10 years through independent Outcomes Centres initially and are currently followed up by our own Centre.

18 patients (24 hips) died 5.9 (0.02 – 11) years after surgery due to unrelated causes, including one patient (1 hip) who was revised and died 5 years after revision. Mean follow-up is 11.9 years (0.8 to 17.8 years). There were 22 revisions altogether (2.1%) at a mean of 6.2 years (0.01 to 14.6 years) including one malpositioned cup in a female patient with developmental dysplasia who dislocated post-operatively and had to be repositioned. 9 hips failed from collapse of the femoral-head and 3 hips from femoral-neck fractures, giving rise to 12 femoral failures in all. There were six deep infections and three bearing-related failures including one pseudotumour, one for osteolysis and one for unexplained pain with neither metallosis nor pseudotumour.

With revision for any reason as the end-point Kaplan-Meier survival analysis showed 98.9%, 98.6% and 97.2% implant survival at 5, 10 and 17 years. Men had better survival (99.1% and 98.1% at 10 and 17 years respectively) than women (97.3% and 95.3%).

17-year cumulative revision rates were higher in patients with a pre-operative diagnosis of dysplasia (6.1%) and AVN (7.6%) compared to all other diagnoses combined (1.5%). Patients with osteoarthritis had the best results (99.5%, 99.3%, 98.4% at 5, 10 and 17 years respectively).

Our study shows that resurfacing arthroplasty is a viable option for hip arthritis in the young with a low incidence of wear-related failures in the long-term.

Introduction

Little is known about variations in blood metal ions following bearing exchange for poorly functioning metal-on-metal hip replacements (MoMHRs). This study aimed to determine the changes that occur in blood and urine metal ion concentrations following MoMHR revision.

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

Metal-metal surface replacement (MoMSRA) continues to be used in young women. Systemic metal ion release and its effects cause concern. Do metal ions crossing the placenta in pregnant women have potential mutagenic effects? The hypothesis is that metal ions pass freely through the placenta and there is no difference in maternal and cord metal levels.

Introduction

Large diameter metal-on-metal hip arthroplasty (LDMMTHA) provides benefits of reduced dislocation rates and low wear. The use of modular systems allows better restoration of hip biomechanics. There have been reports of modular LDMMTHAs with tapered sleeves generating excessively high metal ions, due to possible mismatch between the titanium stem and the cobalt-chrome sleeve and the dual Morse tapers involved. We evaluated metal ion levels in LDMMTHA patients with and without a cobalt-chrome (CoCr) tapered sleeve.

Introduction

Modern metal-on-metal bearing resurfacings have been in use for nearly two decades. Local and systemic metal ion exposure continues to cause concern. We could not find a prospective metal ion study in such patients with a 10-year follow-up. This is the first ten year prospective study of metal ion levels in blood and their release in urine following hybrid fixed metal-on-metal surface arthroplasty.

Introduction

This is a retrospective review of the incidence of deep venous thrombosis (DVT) in 679 consecutive unilateral primary hip arthroplasty procedures performed between January 2007 and December 2010 managed with no anticoagulants. Mean age at operation was 58 years. Mean BMI was 26. The prophylaxis regimen included hypotensive epidural anesthesia, compression stockings, intermittent calf compression, early mobilization and an antiplatelet agent.

Introduction

High early failure rates have been reported with certain metal-metal surface arthroplasties and good results have been reported with others. This is a minimum 10-year review of the first 1000 consecutive resurfacings including all ages and diagnoses from one centre.

Introduction

Wear and corrosion of metal-on-metal (MM) bearings releases (a) soluble metal ions which collect locally and pass into the systemic circulation and (b) insoluble particles which undergo local deposition and lymphoreticular dissemination. Debris-related failures from osteolysis, metallosis and pseudotumours warrants revision of these MM bearing devices to non-MM bearing arthroplasties with the expectation that both the systemic and local effects will be reversed with time since the source of metal ion release is removed.

The purpose of the present study is to determine (a) whether metal ion levels in blood and urine decrease after revision of a MM bearing arthroplasty to a non-MM bearing device and (b) the rate at which this decrease is effected.

Introduction

Hip simulator studies show that metal-on-metal bearing wear can be reduced by reducing the diametral clearance of the bearing. We present the six-year follow-up results of a prospective clinico-radiological and metal ion study in patients with a low clearance metal-metal surface arthroplasty. The results are compared to published results of similar design bearings with conventional clearance.

Introduction

The results of the 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.

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.

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.

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.

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: 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: 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: 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: 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.

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: 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: 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: 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 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: 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: 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.

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.

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.

The recent resurgence in the use of metal-on-metal bearings has led to fresh concerns over metal wear and elevated systemic levels of metal ions.

In order to establish if bearing diameter influences the release of metal ions, we compared the whole blood levels of cobalt and chromium (at one year) and the urinary cobalt and chromium output (at one to three and four to six years) following either a 50 mm or 54 mm Birmingham hip resurfacing or a 28 mm Metasul total hip replacement. The whole blood concentrations and daily output of cobalt and chromium in these time periods for both bearings were in the same range and without significant difference.

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.