In a previous study on impact response of the human knee joint in lateral car-pedestrian collisions a mathematical model of pedestrian lower extremity with a human-like knee joint was presented. The results showed that the model lacked adequate representation of the deformation and fracture of the leg segments since the response was shown to be strongly dependent on whether the leg was fractured or not. In this study, a mathematical model which would also represent a breakable leg was developed and implemented into the pedestrian lower extremity model.

The leg model consists of two rigid-body elements connected by a “fracturable joint”. The moment-deformation characteristics of the “fracturable joint” are described by the user subroutines, which were prepared and added to the MADYMO 3D program system. The input data for the “fracturable joint” model originate from available biological specimen tests.

Computer simulations of car-pedestrian impact with this modified pedestrian model were conducted at a speed of 31 km/h in four different configurations, and compared with previously performed human leg specimen tests. Different types of bumper compliance and bumper levels were simulated. The bumper force. the accelerations, the condyle contact forces and the ligament strains were calculated during simulations. The results showed that the modified model gave a higher biofidelity than did the previous model with the undeformable representation of the leg segments. The calculated parameters such as bumper forces and accelerations corresponded with the measured parameters in tests. The impact response of the lower extremity could be well predicted by the model.