Evidence that in vivo wear damage alters kinematics and contact stresses in a total knee replacement

Polyethylene wear after a total knee arthroplasty is inevitable. The effects of the wear particles on the surrounding soft tissue causing inflammatory responses and eventual aseptic loosening are well documented, but the biomechanical changes from polyethylene wear have been less understood. This study investigated how wear from a retrieved polyethylene insert from a total knee arthroplasty changed the kinematics and contact stresses. A cruciate-retaining total knee implant (Natural-Knee, Intermedics Orthopedics, Inc., Austin, Texas) was retrieved from a donor program. The polyethylene insert was then scanned and modeled. KneeSIM (LifeMOD/KneeSIM, San Clemente, California) was used to simulate one cycle of gait of three second duration (100% of cycle). A threefold increase in contact stress as well as resulting kinematic changes were seen when the model was used to compare the retrieved versus a modeled off-the-shelf new polyethylene insert. Total knee designs should take into account the wear patterns that result from years of use and how they may affect the biomechanics of the knee long term.