There are many mechanisms for ankle injury to front seat occupants involved in automotive impacts. This study addresses injuries to the ankle joint involving inversion or eversion, in particular at high rates of loading such as might occur in automotive accidents. Injuries included unilateral malleolar fractures and ligament tears, and talus and calcaneous avulsions.
Twenty tests have been performed so far, two of them using Hybrid III lower leg and the rest using cadaveric specimens. The specimens were loaded dynamically on the bottom of the foot via a pneumatic cylinder in either an inversion or eversion direction at fixed dorsiflexion and plantarflexion angles. The applied force and accelerations have been measured as well as all the reaction forces and moments. High-speed film was used to obtain the inversiordeversion angle of the foot relative to the tibia and for following ligament stretch.
As was found in the dorsiflexion mode, forces and moments in the ankle do not appear to be well correlated with angular deflection or injuries. Peak axial loads ranged between 270 N and 1300 N, while peak inversion/eversion moments ranged between 9 Nm and 120 Nm. Inversionleversion angles ranged from 30 degrees to 85 degrees. Angular deflection of 60 degrees (+I-6) for both inversion and eversion appears to be the best threshold for injury. The Hybrid III response did not compare well to those of the cadavers.