A Severe Ankle and Foot Injury in Frontal Crashes and Its Mechanism

In frontal automobile collisions, the driver's foot is usually stepping on the brake pedal as a pre-collision instinctive response. The tensile force generated in the Achilles tendon produces a compressive preload on the tibia. If the toe board intrudes after the crash, additional external force is applied to the driver's foot. Using human cadaveric specimens, a series of dynamic impact tests were conducted to investigate the combined effect of muscle preloading and external force. A constant tendon force was applied to the forefoot by a rigid pendulum. Preloading the tibia greatly increased the tibial axial force and the combination of these forces resulted in 5 tibial pylon fractures out of 16 specimens. This loading condition could be one of the mechanisms of tibial pylon fracture which is rated as one of the severest forms in lower leg injuries and which was difficult to reproduce in the laboratory. A finite element model was used to visualize stress distribution in the foot and ankle complex. The boundary conditions in the model were carefully defined to simulate the cadaver test. The force-time history and stress distribution in the ankle were computed and the effect of the tendon force acting in concert with an external axial load was studied. In the presence of a tendon force, the stress was found to be higher in the tibia and lower in the calcaneus.