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W e compared and quantified the modes of failure and patterns of wear of 11 Mittelmeier and 11 Ceraver-Ostal retrieved alumina-alumina hip prostheses with reference to the corresponding clinical and radiological histories.Macroscopic wear was assessed using a three-dimensional co-ordinate measuring machine. Talysurf contacting profilometry was used to measure surface roughness on a microscopic scale and SEM to determine mechanisms of wear at the submicron level.The components were classified into one of three categories of wear: low (no visible/measurable wear), stripe (elliptical wear stripe on the heads and larger worn areas on the cups) and severe (macroscopic wear, large volumes of material lost). Overall, the volumetric wear of the alumina-alumina prostheses was substantially less than the widely used metal and ceramic-on-polyethylene combinations. By identifying and eliminating the factors which accelerate wear, it is expected that the lifetime of these devices can be further increased. The long-term effects of ultra-high-molecular-weight polyethylene (UHMWPE) wear debris and the resulting osteolysis are well documented and have prompted renewed interest in alternative materials for total hip arthroplasty (THA). The alumina-alumina bearing couple was introduced in 1970, 1 but has been used only in small numbers compared with standard metal-on-UHMWPE designs. Laboratory tests and simulator studies have demonstrated the low friction and wear of this prosthesis, but concerns remain about its performance in vivo. Published clinical studies have already established the safety and the good tribological performance of this couple, 2-5 but there are doubts about the long-term performance of aluminaalumina THAs. The most common reasons for revision have been loosening of one or both components. The mechanisms which have led to this loosening have not yet been satisfactorily explained and therefore clinical and retrieval studies are needed to assess the performance of these prostheses in vivo. It is still unclear what role, if any, wear and wear debris play in their long-term performance or indeed if wear is a factor in the loosening process. Our aim was to establish the wear patterns and rates of wear of two different alumina-alumina prostheses to allow future improvements in design and materials. Patients and MethodsExplants. We studied two series of explants from centres in the UK and France. The UK series consisted of 11 explanted bearing couples from a 16-year series of Mittelmeier THAs implanted between 1980 and 1996 at Bradford Royal Infirmary by Mr A. Nevelos. The French series consisted of 11 explanted Ceraver-Osteal bearings implanted between 1977 and 1988 at the Hospital St Louis, Paris, by Professor L. Sedel and Professor Witvoet. Design of the prosthesis. The Mittelmeier Autophor (Ceramtec AG, Plochingen, Germany) design consisted of an externally threaded truncated cone socket made of monolithic alumina ceramic which was screwed into an underreamed acetabulum to articulate with a 32 or 38 mm modular he...

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