Friction reduction in total joint arthroplasty

Wear of ultrahigh molecular weight polyethylene (UHMWPE) bearing surfaces a nd 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 pattern ing on GUR 415 grade UHMWPE friction and wear characteristics under in vitr o dynamic loading conditions. A pin-on-disk wear and friction apparatus was used for the dynamic tests which were conducted at 67-70 degrees F and 60% relative humidity in bovine serum. An undulating surface geometry, consist ing of 2732 0.16-mm diameter, 0.32-mm deep holes, was machined onto the sur face 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 co rresponded to an initial mean Hertzian contact stress of 30 MPa. Friction f orces were recorded throughout the 3-h test period. Following testing, the wear track width, plow height, and wear depth were measured using a profilo meter. The undulating pattern of surface cavities produced a significant re duction (42%) in the friction coefficient in comparison to the non-patterne d UHMWPE surfaces. Such findings are hypothesized to reflect the fact that patterned surfaces act as a reservoir for the lubricating fluid and also tr ap wear particles, minimizing third body-type wear. Under the relatively hi gh load condition examined in this study, however, patterning of the UHMWPE surface was not effective in reducing wear presumably because the polyethy lene surface was plastically deformed by the high contact stresses. (C) 199 8 Published by Elsevier Science S.A. All rights reserved.