Clinical and hip simulator comparisons of ceramic-on-polyethylene and metal-on-polyethylene wear

The benefit of reduced polyethylene wear with ceramic in hip replacements d oes not seem to have been universally appreciated, In this current study, w ear predictions from laboratory and clinical studies were compared for cera mic-on-polyethylene and cobalt chrome-on-polyethylene combinations. Many la boratory studies included water-based lubrication and linear-tracking mecha nisms. Now it is appreciated that these were inappropriate methods, because of a propensity for very low or virtually no polyethylene wear against cer amics in water, Thus, waterbased studies predicting a 20- to 80-fold advant age for ceramic-on-polyethylene compared with metal-on-polyethylene clearly were in error, However, serum-based simulator studies with high protein-co ncentrations generally have shown greater wear with alumina-on-polyethylene than with metal-on-polyethylene. Controversy still remains over the use of such nonphysiologic protein levels, The simulator studies were just beginn ing to explore the role of serum protein concentrations and the influence o n the various wear models, Polyethylene wear with zirconia systems was part icularly affected by serum protein concentrations. In one simulator study, use of proteins in the physiologic range resulted in the alumina-on-polyeth ylene wear rate decreasing to approximately 50% of that of metal-on-polyeth ylene, In the literature, many hip design and polyethylene variations were reported which confounded the wear analysis, Overall, the clinical data sup ported the superior performance of ceramic-on-polyethylene systems by a fac tor of 1.5- to Fourfold. However, the amount of supporting data was not lar ge. This summary of laboratory and clinical data indicated that ceramic-on- polyethylene hip replacement systems offered on average a 50 % wear reducti on from metal-on-polyethylene systems.