Simulation of the wear of metal implants by soft-tissue

This paper describes the simulation and laboratory test protocol used for the investigation of wear of prosthetic materials by soft-tissue. The hypothesis for the phenomenon of soft-tissue wear of the body of massive prostheses was that there were particular combinations of physical contact conditions which led to high metal wear rates. The laboratory simulations allowed us to investigate the wear process and test results compared favourably with explanted prostheses exhibiting wear scars. The conditions governing the wear of titanium by soft-tissue have not hitherto been investigated (Lilley, 1994). The findings from the investigation were surprising and non-intuitive in that metal was severely damaged by soft-tissue attrition. The findings contribute to the understanding of the causes of this type of wear. There is evidence that the hypothesis suggesting low contact loads create higher coefficients of dynamic friction, and subsequent wear, than that occurring with high contact loads was demonstrated and explained by reference to the phenomenon of a stick-slip simulation mechanism. This would offer an explanation of why the explanted prostheses of elderly, low body weight patients, with reduced activity levels, often exhibit more severe wear from the shaft of prostheses than younger, heavier, and more active patients. The experimental findings could also help explain the reasons for patients with apparently similar sets of in vivo biochemical conditions exhibiting extreme differences in debris production and tissue staining (Black et al., 1990).