Mechanisms of aortic injury in fatalities occurring in motor vehicle collisions.

Case reviews based on autopsy studies have shown that motor vehicle collisions cause between 50 and 90% of traumatic aortic ruptures. Very few studies have analyzed the nature and severity of the collision forces associated with this injury. Our passenger car study (1984-1991) examined 36 collisions in which 39 fatally injured victims sustained aortic trauma. In this injury group, a disproportionate number of heavy truck and roadside fixed-object impacts occurred. Vehicle crash forces were generally severe and were either perpendicular or oblique to the vehicle surface. Intrusion into the occupant compartment was a significant factor in most of these fatal injuries. Occupant contact with vehicle interior surfaces was identified in most cases, and occupant restraints were often ineffective, especially in side collisions. The more elderly victims were seen in the least severe collisions. The most frequent site of aortic rupture was at the isthmus. A majority of victims had rib/sternal fractures indicating significant chest compression. Of the various traumatic aortic injury mechanisms proposed in motor vehicle impacts, the favored theories in the literature combine features of rapid deceleration and chest compression. This study supports that predominant impression, concluding that rapid chest deceleration/compression induces torsional and shearing forces that result in transverse laceration and rupture of the aorta, most commonly in the inherently vulnerable isthmus region.