Increased force simulator wear testing of a zirconium oxide total knee arthroplasty

Total knee replacements provide cost effective treatment for debilitating conditions such as osteoarthritis. Their long term performance is governed by ultra-high molecular weight polyethylene (UHMWPE) wear which produces wear debris leading to osteolysis and aseptic loosening of the implant. An oxidised zirconium alternative to cobalt chrome is being used to reduce wear debris formation in the younger patients. Two TKRs of cobalt chrome and two of zirconium oxide coated zirconium were tested in a six degrees of freedom of motion, Stanmore-Instron force controlled knee wear simulator over 4 million increased force cycles. Oxidised zirconium was demonstrated to be more scratch resistant than CoCr. Increases in Ra (mean average roughness) of 12-fold compared to 1.9 fold rise for ZrO. The differences in roughness were accompanied by a 78%, statistically significant, reduction in wear of UHMWPE with the ZrO femoral components compared to the CoCr (p=0.037). Long term clinical results from the use of oxidised zirconium femoral components are awaited. However, it shows potential to reduce the wear rate.