EARLY CLINICAL FAILURE OF THE BIRMINGHAM METAL-ON-METAL HIP RESURFACING IS ASSOCIATED WITH METALOSIS AND SOFT TISSUE NECROSIS

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Introduction: As candidates for arthroplasty become younger and life expectancy increases the required working life of a total hip arthroplasty continues to rise. Hip resurfacing offers potential further advantages in young patients as minimal bone resection makes for easier revision, and the design allows for an increased range of movement. The Birmingham Hip Resurfacing (BHR) is the first of the second generation hip resurfacings. Reports are beginning to emerge of unexplained failure, pseudotumour formation, individual cases of metallosis. Joint registry data also demonstrates an unexplained high early failure rate for all designs of hip resurfacing. This paper examines the rate and mode of early failures of the BHR in a multi-centre, multi-surgeon series. Methods: All patients undergoing BHRs in our two centres were recruited prospectively into our arthroplasty follow up programme. Patients have been followed up radiographically and with clinical scores. Results: Mean radiographic and clinical follow up was to 43 months (range 6 – 90 months). Of the 463 BHRs two have died and three are lost to follow up. Thirteen arthroplasties (2.8%) have been revised. Eight for pain, three for fracture, two for dislocation and one for sepsis. Of these nine were found to have macroscopic and histological evidence of metalloisis. Survival analysis at 5 years is 95.8% (CI 94.1 – 96.8%) for revisions and 96.9% (CI 95.5 – 98.3%) for metallosis. Discussion: Histopathological examination demonstrated a range of inflammatory changes including necrosis, inflammation, ALVAL and metal containing macrophages. Not all features were associated with each patient and it is likely that these features form part of the spectrum of metal wear debris disease. The likely rate of metallosis is 3.1% at five years. Risk factors for metallosis in this series are female sex, small femoral component, high abduction angle and obesity. We not advocate use of the BHR in patients with these risk factors.

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