Wear of fixed bearing and rotating platform mobile bearing knees subjected to high levels of internal and external tibial rotation.

In order to extend the lifetime of total knee replacements (TKR) in vivo, reduction of the volumetric wear rate of ultra high molecular weight polyethylene (UHMWPE) bearings remains an important goal. The volume of wear debris generated in fixed bearing total knee devices increases significantly when subjected to higher levels of internal-external rotation and anterior-posterior displacement. Six PFC Sigma fixed bearing TKR were compared with six LCS rotating platform mobile bearing knees using a physiological knee simulator with high rotation kinematic inputs. The rotating platform polyethylene inserts exhibited a mean wear rate which was one-third of that of the fixed bearing inserts despite having increased femoral contact areas and additional tibial wear surfaces. The rotating platform design decouples knee motions, by allowing unidirectional motion at the tray-insert articulation, which reduces rotation at the femoral-insert counterface. This translation of complex knee motions into more unidirectional motions results in molecular orientation of the UHMWPE and reduced volumetric wear. Copyright 2001 Kluwer Academic Publishers