A significant number of documented ankle injuries incurred in automobile accidents indicate some form of lateral loading is present to either cause or influence injury. A high percentage of these cases occur in the absence of occupant compartment intrusion. To date, no specific ankle injury mechanism has been identified to explain these types of injuries. To investigate this problem, several resources were used including full-scale crash test data, finite element models, and case study field data. Results from car-to-car, offset frontal crash tests indicate a significant lateral acceleration (10-18 g) occurs at the same time as the peak in longitudinal acceleration. The combined loading condition results in a significant lateral force being applied to the foot-ankle region while the leg region is under maximum compression.
The effects of this combined loading on the human lower limbs were investigated using a combined finite element model of the human lower limbs and a Hybrid III dummy. Results indicate that a potential exists for lateral ankle injury in the eversion mode. Maximum sub-talar rotations were as high as 43° for the 50th percentile male and 53° for the 5th percentile female. It was also determined that this mode of injury is not detectable with the current lower limbs of the Hybrid III dummy.