Biomechanics and Outcomes of Modern Tibial Polyethylene Inserts

There have been many attempts to use variations in tibial polyethylene design to better recreate normal knee kinematics in the total knee arthroplasty. The goal of this review is to provide an overview of the various types of tibial inserts that exist and review the theoretical mechanics versus what was demonstrated in vivo.

Many polyethylene inserts have been attempted to re-create normal knee kinematics, but none have been able to successfully do so. Previously the only two types of inserts were posterior stabilized (PS) and cruciate retaining (CR) polyethylene inserts. Both of these have shown excellent long-term survival but neither has demonstrated native kinematics. Initially, it was thought that retention of the posterior cruciate ligament (PCL) would allow for more native kinematics, but fluoroscopic evidence has shown that the PCL alone cannot accomplish this. Newer inserts try to restore femoral roll back and the screw home mechanism. The bicruciate retaining total knee inserts are having the most "normal" kinematics, suggesting the importance of both the ACL and PCL in knee biomechanics. Modern polyethylene inserts show favorable short-term data with bicruciate retaining inserts having the best kinematics; however, long-term studies are still needed to determine if survivorship and patient outcomes remain favorable.