Contact analysis of knee prosthesis capable deep knee flexion using mathematical model

We have developed a new type of knee prosthesis which is capable to make 180° knee flexion, and have designated it as Complete flexion knee (CFK). Since the kinematics and kinetics of knee prosthesis varies depending not only on its articulating surface shape but also on the stiffness of soft tissues, its performance should be assessed under various kinds of lower limb activities. The objective of this study is to perform simulation analysis of level walking, ascending stars and squatting to evaluate the performance of CFK using the 2D/3D mathematical models. Our mathematical model of total knee arthroplastic joint includes the tibio-femoral and patello-femoral compartments. Furthermore, our models allow for the "thigh and calf" contact in deep knee flexion. First, the simulation was performed up to high knee flexion using our 3D model. After that we had to alternate the model from the 3D to the 2D, because the patella stacked into the femoral intercondylar, the thigh-calf contact occurred and the 3D model did not introduce the converged solution. The results demonstrated that at the level walking, post/cam contact did not occur. At the ascending stars, both post/cam and femoral condyle-tibial plateau contact occurred. At the squatting, only post/cam contact occurred and maximum contact stress was 52 MPa.