Analysis of wear asymmetry in a series of 94 retrieved polyethylene tibial bearings

Knee joint kinematics is the focus of a significant amount of experimental study for the purpose of knee prosthesis design and for testing the wear of current and prospective bearing materials. This study reports the wear assessment of a series of 94 explanted tibial bearings of various designs and manufacturers and focuses on the extent to which clinical wear is symmetric in the medial-lateral aspect, or is indicative of a systematic asymmetry that would be informative to the design and testing of knee prostheses or surgical practice. Wear assessment of the series of retrievals indicates that, statistically, there was more clinical wear on the medial side. Patterns of wear varied greatly among individual knees; a majority showed very similar extents of wear on the medial and lateral sides, however there were cases with significantly more wear on one condylar articulation than the other. Evidence of edge loading, whereby the femoral component articulates at the margin of the tibial bearing, was common. It was seen most frequently in the central zone of the medial condylar area, and, like the overall wear, edge loading was significantly more frequent on the medial side of bearings. Total bearing wear was seen to generally increase with time over the 208 months of in vivo duration covered by the retrievals in the study. The medial-lateral asymmetry of the wear does not appear to be significantly dependent on duration, however.