All-polyethylene patellar components are not the answer.

Abstract

Recent reports of the high incidence of polyethylene failure of metal-backed patellar components have rekindled the interest in cemented, all-polyethylene designs. One hundred four retrieved patellar components of metal-backed and all-polyethylene designs were analyzed for wear. Additionally, patellofemoral contact stress as a function of flexion angle was measured for unused components using pressure-sensitive Fuji film. Significant wear (2+ on a 0-3 scale) was seen in 65% of metal-backed designs and in 78% of all-polyethylene components. Severe wear (3) was seen in 44% of all-polyethylene components and in 39% of metal-backed devices. The incidence of severe wear (3) of congruent designs was statistically significantly lower than that of the noncongruent designs. Contact stress analysis confirmed that dome-type geometries typically resulted in stresses that exceed the yield strength of the polyethylene, whereas the more congruent geometries generated significantly reduced stress levels.