Analysis of wear and friction of total knee replacements. Part I. Wear assessment on a three station wear simulator

As part of a project to evaluate novel orthopaedic bearings, a simplified wear simulator has been evaluated and validated using conventional ultra high molecular weight polyethylene (UHMWPE)-cobalt chrome knee replacements. The simulator uses a constant load, applied pneumatically, and provides a combination of rolling and sliding motions. Wear rates measured gravimetrically correlated well with results from other studies. Adhesive wear was the dominant mechanism observed with the tibial inserts, manifested as burnishing of the contact area although features indicative of abrasive wear were also observed. Surface profilometry was used to assess the changes in the topography of the components throughout testing and the surface roughness parameters obtained were correlated to the observed wear. It was shown that the machined UHMWPE inserts were initially polished and, following this run-in phase, became rougher as particles of UHMWPE were continually being pulled from the tibial surface. The wear rates and observed wear features correlate with in vitro studies using simulators with more complex load-cycle profiles and also with in vivo retrievals and, therefore, it is considered that this apparatus is suitable for evaluation of novel bearing systems.