Oxidised zirconium heads show a lower linear wear rate than 28-mm metal heads against XLPE: a retrospective analysis.

Abstract

Aims: The use of highly cross-linked polyethylene (XLPE) on the acetabulum has undoubtedly improved the wear rates and hence survivorship of total hip arthroplasty (THA). However, the importance of head tribology is not known. Oxidised zirconium (OxZr) was introduced to offer the lower wear rates of ceramic but the strength of metal. Whether OxZr heads have any purported benefits in terms of lowering wear is not known. This study therefore aims to compare wear rates of XLPE against metal and OxZr heads over a 10-year period.

Methods: A previous study has suggested we need a minimum 95 cases to show a statistically significant difference. Thus, in this 10-year retrospective analysis we included 95 subjects with a primary THA with a 28-mm OxZr and 131 patients with a 28-mm cobalt-chrome (CoCr) head, both against XLPE liners.Linear and volumetric wear rate comparisons were performed using a validated 2-dimensional stereoisometric analysis by an independent centre.

Results: There were no significant differences for any of the patient demographics between the 2 groups, with >60% women in both groups and normally distributed age. Cup inclination angle was also comparable between the 2 groups.While there was no difference in volumetric wear rates (p = 0.7377), the annual linear wear rate for OxZr was 0.030 mm (95% CI, 0.024-0.036) compared with 0.046 mm (95% CI, 0.038-0.054) for CoCr, a statistically significant difference (p = 0.0002)Conclusions:The widespread use of XLPE has revolutionised THA. This study is the first to show a statistically significantly lower wear rate with the use of OxZr. Whether this is enough to justify the cost differential and whether it translates to better implant survivorship is still to be determined. But if wear limiting wear rates is associated with decreasing revision rates, the use of ceramicised metal may be of clinical benefit.