Abstract
Introduction
Wear of the ultra high molecular weight polyethylene (UHMWPE) cup and the resulting loosening has been shown to limit the long-term results of the Charnley low-frictional torque arthroplasty (LFA). Factors affecting wear rates have been studied: level of patient activity, effective roughness of the stainless steel head, impingement and the possible variations in wear characteristics of UHMWPE. Since patients' activity level cannot be predicted or modified, alternative materials were examined.
Methods and Results
The Charnley 22.225 mm diameter head of alumina ceramic in combination with chemically cross-linked polyethylene cup has now reached over 23 years of clinical and radiographic follow-up. Of the initial 17 patients (19 hips) in the study, 4 patients (4 hips) have died, 1 hip has been revised for deep infection and 3 patients (3 hips) are unable to attend follow-up due to medical problems unrelated to the hip. Nine patients (11 hips) are still attending follow-up at a mean of 22 years 5 months (21 year 3 months-23 years 6 months). The mean age at surgery in this group was 47 years (26-58) and the mean weight 81kgs (54-102). The mean penetration rate was 0.02mm/year and none have exceeded 0.41mm total penetration.
Conclusion
Since the problem of cup wear and loosening is mechanical rather than biological the long-term solutions are more likely to come from materials rather than radical changes of design of methods of component fixation.
