A mechanism of injury to the forefoot in car crashes.

OBJECTIVE The purpose of this study was to determine a mechanism of injury of the forefoot due to impact loads and accelerations as noted in some frontal offset car crashes. METHODS The impact tests conducted simulated knee-leg-foot entrapment, floor pan intrusions, whole-body deceleration, muscle tension, and foot/pedal interaction. Specimens were impacted at speeds of up to 16 m/s. To verify this injury mechanism research was conducted in an effort to produce Lisfranc type injuries and metatarsal fractures. A total of 54 lower legs of post-mortem human subjects were tested. Two possible mechanisms of injury were investigated. For the first mechanism the driver was assumed to be braking hard with the foot on the brake pedal and at 0 deg plantar flexion (Plantar Nominal Configuration) and the brake pedal was in contact with the foot behind the ball of the foot. The second mechanism was studied by having the ball of the foot either on the brake pedal or on the floorboard with the foot plantar-flexed 35 to 50 deg (Plantar Flexed Configuration). RESULTS The Plantar Nominal injury mechanism yielded few injuries of the type the study set out to produce. Out of 13 specimens tested at speeds of 16 m/s, three had injuries of the metatarsal (MT) and tarsometatarsal joints. The Plantar Flexed Configuration injury mechanism yielded 65% injuries at high (12.5-16 m/s) and moderate (6-12 m/s) speeds. CONCLUSION It is concluded that Lisfranc type foot injuries are the result of impacting the forefoot in the Plantar Flexed Configuration. The injuries were consistent with those reported by physicians treating accident victims and were verified by an orthopedic surgeon during post impact x-ray and autopsy. They included Lisfranc fractures, ligamentous disruptions, and metatarsal fractures.