The Dominance of Cyclic Sliding in Producing Wear in Total Knee Replacements

TLDR

Kinematic conditions at femoral‑tibial bearing surfaces vary widely, encompassing rolling and sliding motions. A test machine applied a cyclic 2.2 kN load for 10 million cycles to spherical‑ended metal femoral components against flat polyethylene tibial plates in distilled water. Cyclic loading alone produced a shiny depression, but adding oscillation and sliding caused severe cracking and high wear; rolling motion yielded a shiny track with minimal damage, patterns that match retrieved knee specimens and show that low‑conformity components with laxity are prone to sliding‑induced wear while more‑conforming designs reduce sliding and wear.

Abstract

From a literature survey, it was evident that a wide variety of kinematic conditions occur at the femoral-tibial bearing surfaces, including various degrees of rolling and sliding. A test machine was constructed to reproduce these conditions, applied to spherical-ended metal 'femoral' components acting on a flat polyethylene 'tibial' plateau. The load was cyclic at 2.2 kN for 10 million cycles with distilled water lubricant. For cyclic load only, a shiny depression was formed. With oscillating and sliding superimposed, there was severe surface and subsurface cracking resulting in high wear. When rolling motion was applied, a shiny wear track was formed with minimal cracking and wear. Such surface phenomena were observed in retrieved knee specimens, probably reflecting the kinematics associated with the knee. Low-conformity components inserted with high ligamentous laxity are susceptible to anteroposterior sliding and hence high wear. More-conforming components are less susceptible to wear because they limit sliding as well as reduce contact stresses.