Clinical wear of 63 ultrahigh molecular weight polyethylene acetabular components: effect of starting resin and forming method.

ABSTRACT

This study compares the clinical wear rates and implant characteristics of 63 surgically retrieved acetabular components. All components were made by the same manufacturer, implanted by the same surgeon, in articulation against the same type of femoral component, and revised for the same reason; 19 were made from directly compression molded, calcium stearate free, ultrahigh molecular weight polyethylene (UHMWPE) and 44 were made from machined, ram extruded, calcium stearate containing UHMWPE. There were significant differences in wear, duration, and wear rate between the molded (type I) and machined (type II and III) components. Most importantly, the wear rates of type I (molded) components were significantly (p < 0.0001) lower than the wear rates of type II, type III, and type II and III components as a group (all machined). The machined components had wear rates 2.3 times greater than the molded components. The wear rates between the two different groups of machined components (type II and III) were not significantly different. The scanning electron microscope observations did not reveal any major differences in wear mechanisms between the three types of components, although the machined components did show more evidence of brittleness. The molded components were better consolidated (or had less fusion defects) than the ram extruded components.