WEAR OF POLYETHYLENE ACETABULAR CUPS AGAINST ALUMINA FEMORAL HEADS - 5 PROSTHESES COMPARED IN A HIP SIMULATOR FOR 35 MILLION WALKING CYCLES

5 ultra-high molecular weight polyethylene acetabular cups articulated against alumina femoral heads for 35 million walking cycles in a hip joint simulator designed for wear tests of total hip prostheses. The specimens were from Protek, Biomet, Link, Howmedica and Thackray. In the Howmedica specimen, the wear was zero, and in Link and Thackray practically negligible. In Biomet, however, the wear was noteworthy and in Protek disastrous after 20 million cycles because in these 2 prostheses the head was attached to a titanium-alloy stem by taper-fit: titanium-alloy particles that were removed from the taper because of micromotion between the head and stem were entrapped between the head and cup, adhering to the head and making it rough, which led to severe abrasive wear of the Protek cup. It was worn through at 26 million cycles, the total wear being 3,170 mg. In Biomet, Link and Thackray, the total wear was 124, 5.3 and 17.6 mg, respectively. Polyethylene wear particles may lead to adverse tissue reactions and eventual loosening of the implant. The results indicate that by the use of alumina heads, polyethylene wear can be eliminated, but this advantage may be lost if the head is attached to a titanium-alloy taper.