Tribological characteristics of polyethylene bearings of knee prostheses

This paper deals with the problem of tribological failure of artificial knee prostheses. The clinical problem is introduced by analysis of worn knee bearings made of ultra-high molecular weight polyethylene. Three different failure mechanisms are described: subsurface-originated contact fatigue failure, surface-originated wear of the articulating surface, and surface-originated wear of the back (non-articulating) surface. The wear processes were simulated in a rolling/sliding wear tester built for this specific purpose. The influence of gamma-irradiation dose on wear and contact fatigue was determined. Wear was greatest at the portion of the wear track where the lubricating fluid film was thinnest and a boundary or mixed lubrication regime prevailed.