It is remarkable that the material, ultra high molecular weight polyethylene (UHMWPE), not specifically formulated for use in the human body, has withstood nearly 50 years under conditions of human activities and function of the hip joint. UHMWPE followed the rapidly wearing PTFE. The possibility of long-term problems resulting from wear, were considered. In the initial reports of this method of treatment the emphasis was primarily on the design of the components, surgical technique, clinical results and the early complications.

In the first publication of the clinical results [1] (1972), wear of the cup was established from examination of annual radiographs. The range of total penetration was from 1 mm in 5 years to no measurable wear in 7 years. The mean penetration rate was 0.13 mm/year. Direct wear measurements were carried out on seven explanted cups.

Increasing follow-up generated revisions and offered an opportunity to study explanted components in detail. It was becoming clear that wear and loosening of the UHMWPE cup was the most likely long-term problem. It was, therefore, essential to study factors affecting wear; the information would be essential for further developments.