Friction reduction in total joint arthroplasty

Abstract

Wear of ultrahigh molecular weight polyethylene (UHMWPE) bearing surfaces and cytotoxic effects associated with wear particles are believed to play a significant role in the mechanical failure of artificial joint prostheses. The objective of this study was to determine the effects of surface patterning on GUR 415 grade UHMWPE friction and wear characteristics under in vitro dynamic loading conditions. A pin-on-disk wear and friction apparatus was used for the dynamic tests which were conducted at 67–70°F and 60% relative humidity in bovine serum. An undulating surface geometry, consisting of 2732 0.16-mm diameter, 0.32-mm deep holes, was machined onto the surface of six of the 12 disk specimens tested. Disk specimens were tested at 112 rpm (0.11 ms −1) using a Co–Cr–Mo pin contact load of 56.5 N, which corresponded to an initial mean Hertzian contact stress of 30 MPa. Friction forces were recorded throughout the 3-h test period. Following testing, the wear track width, plow height, and wear depth were measured using a profilometer. The undulating pattern of surface cavities produced a significant reduction (42%) in the friction coefficient in comparison to the non-patterned UHMWPE surfaces. Such findings are hypothesized to reflect the fact that patterned surfaces act as a reservoir for the lubricating fluid and also trap wear particles, minimizing third body-type wear. Under the relatively high load condition examined in this study, however, patterning of the UHMWPE surface was not effective in reducing wear presumably because the polyethylene surface was plastically deformed by the high contact stresses.