O1221 IMPLANT FACTORS INFLUENCING THE WEAR RATE OF THE POLYETHYLENE IN THE CUP OF TOTAL HIP REPLACEMENT

Abstract

Aims: It is well established that implant characteristics influence the Volumetric Wear Rate (VWR) of the polyethylene cup at the Total Hip Replacement (THR). In order to explore these, a retrieval study in 63 patients having revision THR was carried out. Methods: 45 intact THR components were retrieved from patients after revision THR. The polyethylene VWR was assessed in the laboratory using the shadowgraph technique. Implant features such as femoral head size, stem/cup modularity and liner thickness were recorded. Statistical analysis to identify potential correlations with the VWR was performed. Results: 22 mm diameter femoral heads produced significantly lower VWR values than 28 mm (p=0.006) and 32 mm (p< 0.001), however, there was no significant difference between the 28mm and 32mm (p=0.375) heads. There was no statistically significant difference between the mean VWR in the metal-backed and the all-polyethylene cups with the first 25% higher than the second. However, the femoral stems with a modular head generated a VWR about 3.5 times higher than the solid monoblock femoral components (p< 0.001). Polyethylene thickness didn’t influence statistically significantly the VWR (p=0.135). Conclusions: Modular implants with large femoral head size significantly influence the polyethylene wear rate. However, in this study, the liner thickness did not influence the wear rate, although it is recognised that there is probably a critical thickness below which wear is accelerated.