Ceramic-on-metal hip replacements (COM, where the head is a Biolox Delta ceramic and liner is Co Cr alloy), have demonstrated reduced wear under standard conditions in vitro compared to metal-on-metal (MOM) [1]. Early clinical results are also encouraging [2]. Recently concerns have been raised regarding the poor clinical performance of MOM hip resurfacings [3], particularly when cups are steeply inclined. Laboratory hip simulator testing has been used to replicate edge loading, also demonstrating elevated wear [4]. Therefore, a range of conditions to replicate sub-optimal use clinically to better predict in vivo performance should be used. The aim of this study was to compare the wear rates of MOM and COM under adverse edge loading conditions in an in vitro hip simulator test. Ceramic-on-metal (n=3) and metal-on-metal (n=3) 36mm hip prostheses (supplied by DePuy International Ltd, UK) were tested in the Leeds Physiological Anatomical Hip Joint Simulator. Liners were mounted to provide a clinical angle of 45o, and stems positioned anatomically. A simplified gait cycle and microseparation was applied as previously described [5] for two million cycles in 25% new born calf serum. Gravimetric analysis was completed every million cycles and wear volumes calculated.INTRODUCTION
METHODS
