The prevention of lower extremity injuries to front seat car occupants is a priority because of their potential to cause long term impairment and disability. To determine the types and mechanisms of lower extremity injuries in frontal collisions, studies under controlled test conditions are needed. Sled tests using belt restrained cadavers and dummies were conducted, in which footwell intrusion was simulated via a plane surface or simulated brake pedal. Human cadavers in the age range from 30 to 62 years and Hybrid III dummies were used.

The footwell intrusion had both translational (135 mm) and rotational (30 degrees) components. Maximum footwell intrusion forces and accelerations were measured. The lower legs were instrumented with accelerometers and a “six axis” force-moment transducer was mounted in the mid shaft of the left tibia. Maximum footwell intrusion forces between 7.4 and 20 kN and accelerations between 31 and 132 g were measured, with the greater values corresponding to the dummy experiments. The maximum axial forces in the tibia amounted to 3.4 – 4.9 kN and the resultant maximum moments were between 61 and 450 Nm. The dummies exhibited significantly higher values than the cadavers.

In the cadaver tests the ankle was dorsiflexed from a neutral position by between 55 and 66 degrees due to the intrusion. The forcing of the ankle joint beyond its normal maximum dorsiflexion angle of approximately 20 degrees results in cartilage contusions, shearing off of the talus and the tibia, fractures of the medial and lateral malleoli, and laceration of the spring ligament. The degree of injury severity depended upon the amount of dorsiflexion and the age. The brake pedal simulation resulted in greater dorsiflexion than the plate intrusion and thereby in a higher injury severity.