Biomechanics of foot/ankle trauma with variable energy impacts

A total of 60 pendulum impacts to the plantar surface of 15 lower limb PMHS specimens were conducted. Impact conditions were chosen to obtain data from high velocity tests without injury. For 19 impacts the specimen was initially positioned in 20-deg of dorsiflexion. The remaining impacts used neutral positioning. The foot-ankle response was investigated based on impact energy and velocity. Response was characterized by heel pad and joint stiffness. For neutral tests, axial force vs compression corridors were developed for 2-3 m/s, 4-6 m/s, and 7-63 J impacts. For dorsiflexion tests corridors of 1-3 m/s, 6-8 m/s, 7-20 J, and 80-100 J were developed. These results indicate foot/ankle response is not more sensitive to impact energy than velocity. Injury risk curves were developed for both neutral and dorsiflexion positioning using logistic regression. Strain gage data were used to obtain uncensored force values for injury analysis. In neutral, 50% probability of injury occurred at 6800 N. In dorsiflexion, 50% probability occurred at 7900 N, but the regression was not statistically significant. These preliminary results indicate dorsiflexed specimens fracture at a higher force than neutral specimens.