Microseparation of the centers of alumina-alumina artificial hip joints during simulator testing produces clinically relevant wear rates and patterns

To justify the use of new materials or designs of total hip arthroplasties, in vitro test methods always should replicate wear rates, patterns, and mechanisms seen clinically. Retrieved first-generation alumina-alumina hip joints typically have shown a stripe of wear on the femoral heads, an associated worn area in the acetabular cup, and a low incidence of osteolysis. The wear rates of well-positioned retrieved alumina-alumina prostheses have been reported to be on average 1 to 5 mm³ per annum, which is at least an order of magnitude lower than average wear rates of metal—ultra-high-molecular-weight polyethylene (UHMWPE) prostheses. Publications of in vitro test data to date have shown even lower wear rates, however. The aim of this study was to reproduce clinically relevant wear in a physiologic hip simulator to test the new generation of devices more thoroughly. This is especially important as novel prostheses, such as those using alternative materials and geometries, are being proposed for younger patients.