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.

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: 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.