The influence of slip velocity on wear of total knee arthroplasty

Slip velocities between the condyle and tibial plateau in total knee replacements are suspected to play a major role in wear generation. In this study, the velocity profiles from three different sources were calculated: directly from the input of the international standard ISO 14243-3 (knee wear testing in displacement control), from the kinetics of a simulator running under ISO 14243-1 (load control), and from data derived from three gait tested patients. Slip velocity and contact load showed similar patterns for all three sources, resulting in only moderate differences in the product of both, the force-velocity profile. Based on these finding, a constant vertical load and three different velocity ranges were applied onto three UHMWPE specimens in a wheel-on-flat simulator set-up. After 1 million cycles of testing, optoelectronic measurements revealed more wear in areas of high slip velocity and near zero slip velocity where a transition from rolling to sliding took place. Further, it was found that the coefficient of friction was influenced by the total velocity range.