Backside Damage Corresponding to Articular Damage in Retrieved Tibial Polyethylene Inserts

Abstract

Although motion between the polyethylene insert and tibial baseplate is one probable cause of backside wear, articular contact stresses and kinematic conditions may be additional factors. However, comparisons of articular and backside damage patterns are limited. We report the effect of physiologic loading on the modular capture mechanism and distribution of articular and backside surface damage patterns on retrieved tibial components. We evaluated damage patterns on 37 tibial inserts with a full peripheral rim capture mechanism, including six autopsy-retrieved components that were not previously disassembled and were available for mechanical testing. The duration of physiologic loading affected the modular capture mechanism and damage patterns. Backside damage revealed evidence of a mechanical interlock between the polyethylene insert and tibial tray consistent with the measured insert motion. In autopsy components retrieved after 2 to 6 years, inserts with the least motion had the longest duration of in vivo function and the largest backside damage area. The backside damage area and location corresponded to articular damage with damage patterns concentrated on the posterior half of the polyethylene inserts. Substantial differences between the articular and backside damage modes suggest different wear mechanisms exist at the two interfaces during physiologic loading.