Mechanical stability of well-functioning tibial baseplates from postmortem-retrieved total knee arthroplasties

In joint replacement, cyclic motion at the bone-prosthesis interface is considered a precursor to component loosening. This study characterized the mechanical stability of 13 total knee arthroplasties harvested postmortem after an average time in situ of 10.3 years. With loads applied to the medial and then the lateral tibial plateau, motion between the tibial component and underlying bone was measured with extensometers. The amount of motion between the tibial component and underlying bone under medial and lateral loads of 500 N and then twice body weight was typically less than 20 microm. Tray depression under load application and the liftoff on the contralateral side indicated that the tibial stems limited implant rotation and that implant fixation did not deteriorate with time in situ.