A Study of Knee Joint Kinematics and Mechanics using a Human FE Model 2005-22-0006

Posterior translation of the tibia with respect to the femur can stretch the posterior cruciate ligament (PCL). Fifteen millimeters of relative displacement between the femur and tibia is known as the Injury Assessment Reference Value (IARV) for the PCL injury. Since the anterior protuberance of the tibial plateau can be the first site of contact when the knee is flexed, the knee bolster is generally designed with an inclined surface so as not to directly load the projection in frontal crashes. It should be noted, however, that the initial flexion angle of the occupant knee can vary among individuals and the knee flexion angle can change due to the occupant motion. The behavior of the tibial protuberance related to the knee flexion angle has not been described yet. The instantaneous angle of the knee joint at the timing of restraining the knee should be known to manage the geometry and functions of knee restraint devices. The purposes of this study are first to understand the kinematics of the knee joint during flexion, and second to characterize the mechanics of the knee joint under anterior-posterior loading. A finite element model of the knee joint, extracted from the Total Human Model for Safety (THUMS), was used to analyze the mechanism. The model was validated against kinematics and mechanical responses of the human knee joint. By tracking the relative positions and angles between the patella and the tibia in a knee flexing simulation, the magnitude of the tibial anterior protuberance was described as a function of the knee joint angle. The model revealed that the mechanics of the knee joint was characterized as a combination of stiffness of the patella-femur structure and the PCL It was also found that the magnitude of the tibial anterior protuberance determined the amount of initial stretch of the PCL in anterior-posterior loading. Based on the knee joint kinematics and mechanics, an interference boundary was proposed for different knee flexion angles, so as not to directly load the anterior protuberance of the tibial plateau in restraining of the knee. A frontal crash simulation was performed using a partial vehicle model with the THUMS seated. The performance and effects of the knee airbag, as one of the candidates for knee restraint devices, were evaluated through the simulation.