Session VII - Foot & Ankle

Foot and Ankle Injury Mechanisms in Frontal Car Collisions

John McMaster, MD, FRCS; Chris G. Moran, MD, FRCS;W. Angus Wallace, MD, FRCS; Lucy Wheeler, MSC, Department of Orthopaedic and Accident Surgery, Nottingham, United Kingdom

The aim of this study was to assess the mechanisms responsible for severe foot and ankle injuries in frontal car collisions.

Recent studies have highlighted the vulnerability of the foot and ankle in frontal car collisions. Despite car design and restraint systems reducing fatalities, the frequency of lower extremity injury is increasing. Of particular concern is the frequency of below knee injuries that are associated with high levels of long-term impairment. These injuries result in high personal and socioeconomic costs.

It has been demonstrated that a large proportion of severe injuries occurred in front seat occupants who were braking, or braced against the footwell, at the moment of impact. We therefore attempted to recreate these conditions in the laboratory. Twenty-five cadaveric legs were subjected to an axial impact pulse similar to that seen in a narrow overlap frontal collision. To simulate the effect of pre-impact bracing against the control pedals or the footwell, each leg was pre-loaded using approximately1500N of simulated Achilles tension. Other than the use of three impact positions, the test set-up was standardised. Both the impact rig and cadaveric leg were instrumented to allow an assessment of loading rates, peak force, ankle rotation and time of fracture. In addition further information was available from X-ray, CT and necropsy.

The following injuries were generated from this series of tests: 9 intra-articular calcaneal fractures, 1 talar neck, 2 talar body fracture, 3 pilon fractures, 4 malleolar fractures, 4 soft tissue injuries, and 2 had no detectable injury. The injuries sustained in this study are considerably different from previous biomechanical studies investigating axial loading of the leg.

Pilon, talar body and talar neck fractures were generated with impacts anterior to the ankle centre. These fractures occurred before maximum dorsiflexion was achieved. Calcaneal fractures were seen to occur directly through axial loads to the body of the calcaneus, and indirectly >from impacts to the mid-foot.

The results from our study indicate that active musculature is important in the generation of severe foot and ankle injury.