Analysis of wear in retrieved mobile and fixed bearing knee inserts

One purported advantage for mobile bearing (MB) knee implants is reduced polyethylene wear. Twenty-three retrieved Low Contact Stress (LCS) MB and 31 Anatomic Modular Knee (AMK) fixed bearing tibial polyethylene inserts, both Enduron (Depuy, Warsaw, IN) and sterilized by gas plasma, were graded for top and backside wear using the Hood grading system. For articular surface wear, there was no statistical difference between pitting and scratching, but burnishing was twice as much for MB inserts (P = .003). For backside scores, there was a minimal amount of pitting for both, but the scratching score was twice (P = .000) and the burnishing score was 3 times greater for MB inserts (P = .000). At more than 5 years in situ, the linear wear measurements were similar for the 2 groups (mean penetration was 0.329 mm for MB and 0.320 mm for fixed bearing).