Total Knee Replacement Polyethylene Stresses During Loading in a Knee Simulator

We investigated the stresses and kinematics of a total knee replacement during the duty cycle of a knee simulator. Finite element models were constructed of the tibial and the femoral component of a commercially available cruciate retaining total knee replacement. Time dependent flexion/extension, axial loading, and anterior/posterior loading were applied to the components of the arthroplasty to match those generated by the knee simulator. We evaluated the effect of varying the stiffness of a spring-loaded bumper system for anterior-posterior constraint on the joint kinematics as well as on the stresses within the polyethylene tibial component. Both the joint kinematics and the stresses and strains subjected to the polyethylene tibial component, were found to be comparatively insensitive to the stiffness of the spring bumper system for this design. When the stiffness of the bumper system was increased by two orders of magnitude, the maximum contact stresses, von Mises stresses, and von Mises strains in the polyethylene tibial component varied by only 15 to 59 percent. In general, increasing the stiffness of the bumper system decreased the displacements of the base plate, but the relationships were nonlinear, possibly due to the added constraints imposed by the tibiofemoral contact interaction. The long-term goal of this research is to develop a validated structural model to predict the stresses, kinematics, and ultimately, the wear, of total joint replacement components in a contemporary knee joint simulator.