 The purpose of this study is to compare the performance and compare the wear characteristics of two polyethylene cup liners, MarathonTM and EnduronTM, in the treatment of patients with hip joint disease requiring a total hip replacement. Patients who enter the study will be randomly allocated to one of the polyethylene cup liners, MarathonTM or EnduronTM and will be evaluated at regular intervals using clinical and x-ray assessments. 