Wear of fixed bearing and rotating platform mobile bearing knees subjectedto high levels of internal and external tibial rotation

In order to extend the lifetime of total knee replacements (TKR) in vivo, r eduction of the volumetric wear rate of ultra high molecular weight polyeth ylene (UHMWPE) bearings remains an important goal. The volume of wear debri s generated in fixed bearing total knee devices increases significantly whe n subjected to higher levels of internal-external rotation and anterior-pos terior displacement. Six PFC Sigma fixed bearing TKR were compared with six LCS rotating platform mobile bearing knees using a physiological knee simu lator with high rotation kinematic inputs. The rotating platform polyethyle ne inserts exhibited a mean wear rate which was one-third of that of the fi xed bearing inserts despite having increased femoral contact areas and addi tional tibial wear surfaces. The rotating platform design decouples knee mo tions, by allowing unidirectional motion at the tray-insert articulation, w hich reduces rotation at the femoral-insert counterface. This translation o f complex knee motions into more unidirectional motions results in molecula r orientation of the UHMWPE and reduced volumetric wear. (C) 2001 Kluwer Ac ademic Publishers.