Analytical study on the kinematic and dynamic behaviors of a knee joint.

A knee model in the sagittal plane is established in this study. Specifically, the model is used to study the effects of inertia, articular surfaces of the knee joint, and patella on the behaviors of a knee joint. These behaviors include the joint surface contact point, ligament forces, instantaneous center and slide/roll ratio between the femur and tibia. Model results are compared to experimental cadaver studies available in the literature, as well as between the quasistatic and dynamic models. We found that inertia increases the sliding tendency in the latter part of flexion, and lengthens the cruciate ligaments. Decreasing the curvature of the femur surface geometry tends to reduce the ligament forces and moves the contact points towards the anterior positions. The introduction of the patellar ligament in the model seems to stabilize the behaviors of the knee joint as reflected by the behavior of the instant centers and the contact point pattern on the tibia surface. Furthermore, we found that different magnitudes of the external load applied to the tibia do not alter the qualitative behaviors of the knee joint.