Wear of the polyethylene acetabular cup. Metallic and ceramic heads compared in a hip simulator.

Ultra-high molecular weight polyethylene acetabular cups of 5 different total hip systems (Müller, Mallory-Head, Lubinus, P.C.A. and Charnley-Elite) were worn on a new 5-station hip joint simulator. The cups articulated against modular metallic (stainless steel in Müller and Charnley-Elite, ion-implanted Ti-6Al-4V in Mallory-Head, and Co-Cr-Mo in Lubinus and P.C.A.) and modular alumina ceramic femoral heads for 3 million walking cycles. The mean wear rate of cups against alumina heads (range 0-5.7 mg/10(6) cycles, corresponding to 0-0.008 mm/year) was usually lower than against metallic heads (range 3.9-178 mg/10(6) cycles, corresponding to 0.005-0.24 mm/year). In the metal-head prostheses, the mean wear rate was highest against stainless steel heads, and lowest against ion-implanted Ti-6Al-4V heads. As the wear rates are compared with published clinical observations, it can be concluded that the hip joint simulator is capable of producing realistic wear rates; it is a useful instrument in the study of the wear behavior of new designs, materials, surface treatments and coatings prior to clinical trials. However, the taper-fit attachment of modular heads proved problematical, showing corrosion and wear at the conical head-spigot interface.