Surface characterization of metal-on-metal hip implants tested in a hip simulator

Abstract The purpose of this study was to characterize metallurgical and tribological events occurring at the articulating surfaces of metal–metal implants tested in a hip simulator in order to gain understanding of the wear characteristics of Co–Cr–Mo alloys. The surfaces of 12 implant heads, made of either cast, low carbon wrought, or high carbon wrought Co–Cr–Mo material, were examined using scanning electron and atomic force microscopes. Three of the implants were examined prior to simulator testing, three after three million cycles of testing, and six after six million cycles of testing. Initially the carbides in the cast and high carbon wrought components were proud of the surface. With testing, in the high carbon wrought components, the carbides were worn below the matrix surface and were also a source for micropits. In the cast components, some of the carbides remained proud of the surface, while others were worn below the matrix surface with increased test cycles. Some of the carbides in the cast alloy experienced partial or full pull-out, resulting in micropits. All three alloys showed evidence of matrix wear through a process resembling delamination in which layers of material appeared to be removed.