Injuries to the lower extremity accounted for a major proportion of the casualties in vehicle-pedestrian accidents. Impact injuries to this body region are rarely fatal, but they often result in a relatively high social costs due to the consequence of impairment and disability as well as workloss. A pedestrian protection should therefore be given priority. In the paper the mechanisms of injury and the injury tolerances of the lower extremity in car-pedestrian accidents are described and analyzed. Based on the analyses of injury mechanisms, a 3D mathematical model of lower extremity with human-like knee joint and breakable leg elements was developed. The model of the knee joint includes the articular surfaces, ligaments and capsule represented by the ellipsoid and plane elements as well as the spring-damping elements. The leg is represented by two rigid-body elements connected by a joint in which the leg deformation under lateral impact is defined. The mechanical properties of the model are based on available biomechanical data.

Validation of the new developed model was made with results from previously performed experiments with biological specimens. The computer simulations of these experiments were carried out with the model using the MADYMO 3D program. The bumper impact force, the leg acceleration, the condyle interface forces, the ligament forces and the ligament relative elongation were calculated and compared with the results from experiments with biological specimens. The calculated values from simulations correspond in general to measured parameters in experiments.

The model showed a higher biofidelity than the traditional MADYMO model of the lower extremity with a cardan knee joint and an undeformable representation of the leg. The model can be used to investigate impact response of the lower extremity under varying impact conditions. The injury risk of the lower extremity in car-pedestrian accidents can also be predicted by the model.