Evaluation of the distribution of forces on the foot under axial impact loading to assess variations among altered ankle postures between two ATD models

Anthropomorphic Test Devices (ATDs) are used to assess injury risk during impact scenarios, such as motor vehicle collisions. Risk of foot/ankle injuries in these scenarios is traditionally evaluated by analyzing the peak axial force and the Tibia Index, collected from tibia load cells. This neglects assessment of foot injury risk and does not account for potential changes in injury assessment at altered postures. Two commonly used ATDs, the Hybrid III and Military Lower Extremity, were exposed to impacts at five different ankle postures, at varying degrees of flexion. An array of piezoresistive sensors located on the insole of a boot was employed to assess the load distribution variations between postures and ATD models. Both posture and ATD model affected the load distribution on the foot, highlighting the need to establish injury limits for non-neutral postures. The increase in forefoot loading during plantarflexion was not reflected in the standard industry metrics, suggesting that increased fracture risk to the forefoot would not be detected. The differences in load distribution between the models also emphasizes the importance of selecting the correct surrogate. These data will be useful for establishing ATD measures that correspond to future PMHS injury tests at altered postures.