Computer Simulation of Shearing and Bending Response of the Knee Joint to a Lateral Impact

The shearing and bending injury mechanisms of the knee joint are recognised as two important injury mechanisms associated with car-pedestrian crash accidents. A study on shearing and bending response of the knee joint to a lateral impact loading was conducted with a 3D multibody system model of the lower extremity. The model consists of foot, leg and thigh with concentrated upper body mass. The body elements are connected by joints, including an anatomical knee joint unit that consists of the femur condyles, tibia condyles and tibia1 intercondylar eminence as well as ligaments. The biomechanical properties of the model were derived from literature data.

The model was used to simulate two series of previously performed experiments with lower extremity specimens at lateral impact speeds of 15 and 20 km/h. In simulation of lateral shearing response of the knee joint, an impact shearing force was applied to the knee element and the shearing displacement between articular surfaces was calculated. The predicted peak shearing displacement was 8 - 9 mm during the first 10 ms of the impact. This displacement is the main effect of the intra-articular failure of the knee joint to the lateral shearing force. In simulations of response of the knee joint to lateral bending load, the predicted lateral bending angle was about 8 -13 degrees at 20 ms after impact, the corresponding strain of the medial collateral ligament (MCL) was 12 - 15%. The results confirmed that bending failure of the knee is dominated by the knee lateral rotation during the period of 15 - 50 ms after impact. The outcomes from the simulations are analysed and discussed in terms of the injury mechanisms of the knee joint.

The mathematical modelling of the response of the knee joint to transient shearing and bending loads gives a better understanding of the injury mechanism of this body region in car-pedestrian accidents, and it is able to predict the risk of knee injuries corresponding to these two mechanisms.