ABSTRACT
The primary bearing couple that has been used in artificial joints over the last 40 years is a polished metallic convex femoral surface on a concave ultra high molecular weight polyethylene (UHMWPE) acetabular or tibial surface. This was first introduced in hip prostheses in the early 1960s, and since the early 1970s has also been used extensively in knee prostheses. An estimated number of over one million bearing couples are implanted in patients every year, and these remain one of the most successful surgical applications of any biomaterial. Over the majority of this 40-year period, wear of the UHMWPE bearing surfaces has not been considered to be a major clinical problem. The historical linear wear of polyethylene bearing surfaces has been between 0.1 and 0.2 mm/yr, and with UHMWPE bearing components having thickness of up to 10 mm, it could take 50-100 years to wear out an average bearing. This is well beyond the expected life time of the majority of patients. This perceived adequate tribological performance of UHMWPE bearing surfaces has meant that historically alternative bearing couples such as metal on metal or ceramic on ceramic had limited clinical application.
