Mathematical simulation of knee responses associated with leg fracture in car-pedestrian accidents

A new mathematical model of a pedestrian with a breakable leg and a human-like knee was developed to simulate the fracture of the leg in a car-pedestrian impact, and knee responses associated with leg fracture in such an impact to the leg. The leg model consists of two elements connected by a frangible joint. The characteristics of the frangible joint are described by a moment-rotation function; this is based on the leg fracture tolerance data from tests with leg specimens. The knee model origin was based on the anatomical structure of the knee; it represents a femoral condyle-ligament-tibial condyle complex. The pedestrian mathematical model was implemented using the MADYMO 3D program and verified against previous impact tests with biological specimens at a speed of 31 km/h. In the simulation of leg fracture, calculated ligament strain was 9% for MCL (medial collateral ligament), and 25% in the simulation without leg fracture. Contact forces between the lateral articular surfaces in the case of no leg fracture were about 85% higher than in the case of leg fracture. Results from computer simulations confirmed that the impact response and injury mechanism of the knee joint are dependent on whether or not the leg is fractured. The breakable leg model gave a higher biofidelity than did the original one-legged pedestrian model with an undeformable representation of the leg segment.

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