Foot And Ankle Injuries In Variable Energy Impacts

Kathryn Gallenberger, Marquette University


A total of 60 pendulum impacts to the plantar surface of 15 lower limb PMHS were conducted. Impact conditions were chosen to obtain data from high velocity tests without injury to model an under-vehicle landmine blast. For 19 impacts the specimen was initially positioned in 20-deg of dorsiflexion. The remaining impacts used neutral positioning.

The foot and ankle response was investigated based on impact energy and velocity. Response was characterized by heel pad and ankle 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 and ankle response is not more sensitive to impact energy than velocity. Lower limb manikins should be sensitive to both heel pad and ankle joint stiffness.

Fourteen calcaneus fractures and two tibia fractures were observed. Injury risk curves were developed for both neutral and dorsiflexion positioning using logistic regression. Strain gage data were used to obtain uncensored force values. In neutral, 50% probability of injury occurred at tibia axial force of 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.