Volume 8, Issue 3 (March 2011)
Wear Advantage of a Rotating Bearing Knee–An In Vitro Study
Mobile-bearing knees such as rotating platform knee (RPK) prosthetic implant systems were developed to improve knee kinematics, reduce torque transmitted to the implant-bone interface, allow implant self-alignment, and reduce wear. This study evaluated the wear performance of a RPK implant [the Optetrak® (RBKTM)] characterized by a wave-shaped distal bearing intended to reduce the risk of central tibial insert peg wear by shielding it from loading. This system was compared to its clinically proven fixed-bearing knee counterpart (the FBK) (1) as well as other historical RPKs (2). Wear tests were conducted by an independent laboratory using a procedure following ISO 14243-1 with the exception of the fluid test medium. The laboratory disclosed individual wear rates for historical RPK systems (n=9). After correcting for fluid test medium absorption, the net wear rate averaged 2.11±0.47 and 3.00±0.47 mg/Mc for the RBK and the FBK, respectively (P>0.05), while the mean wear rate reported for the historical RPK systems was 6.65 mg/Mc. Visual analysis after testing showed all evaluated RBK inserts exhibited identical contact patterns. Microscopic visual examination revealed minimal central peg and tibial tray bore wear. Based on this study, wear performance was similar for both the RBK and FBK systems. Compared to historical RPKs, the RBK was associated with a lower wear rate, demonstrating that the wave-shaped bearing reduces wear caused by contact between the central peg and tibial tray bore (when tested on a knee simulator).