A detailed finite element (FE) model has been developed of the human lower leg in order to investigate the mechanisms that cause severe ankle injuries in frontal impacts. Predictions from the model have been validated against the results from two separate sets of sub-injurious and injurious PMHS tests. The model correlated well against the test results and it was estimated that a predicted von Mises stress of 120 MPa correlates to a predicted risk of injury to the calcaneus and talus bones in the model. A series of predictive model runs were also carried out to investigate the influence that environmental and subject variations have on the predicted injury risk of the ankle. The set-up of all these model runs were based on sled impact tests in which PMHS legs were mounted on a sled rig with the feet resting on a heel and mid-foot pad. The environmental investigations included model runs with and without the heel pad and loading the foot in eversion and a neutral position. Subject variations investigated the influence that the stiffness of the ligaments joining the mid-foot to the hind-foot have on the predicted injury risk. Without the heel pad there was considerable dorsiflexion of the foot and a predicted increased injury risk to the neck of the talus and a reduced injury risk to the calcaneus. Loading the foot in eversion it was predicted that the greatest injury risk was to the lateral aspect of the talus where the lateral malleolus of the fibula articulates with the talus. Increasing the ligament stiffness reduced the shearing motion in the joints between the mid-foot and the hind-foot and there was an increased injury risk to the neck of the talus.
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