Kevin J. McClafferty

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.

Pedestrians In Real World Collisions

The University of Western Ontario Accident Research Team investigated motor vehicle collisions resulting in a personal injury (PI) or fatality (F). Injury and collision data were analyzed for 198 injury-producing passenger car or light truck/van collisions with pedestrians (96 F; 102 PI). The majority of the fatal collisions occurred on roadways, often when pedestrians were crossing or walking along the travel lanes. In contrast, the majority of the personal injury cases occurred at intersections. Elderly pedestrians were found to be over-represented in the fatal cases in comparison with the personal injury cases. Fatal pedestrian collisions at night were found to be over-represented in comparison with the representative PI cases. In more than 90% of the fatal cases pedestrians were struck by the front of the vehicles and they had either wrapped around the front end onto the hood or projected forward and struck the ground. The wrap trajectory was more frequent in the passenger car collisions, and the forward projection was more frequent in the light truck/van collisions. If there was vehicle damage resulting from the impact it almost always meant serious injury or fatality. Body contacts causing injury were typically to the hood or hood edge, roof rail, A-pillar, windshield, bumper, and ground. The head was the body region most often seriously injured, with more than 80% of all fatally injured pedestrians suffering a head injury of AIS score 2 or greater. In the PI cases, the injured pedestrians most frequently sustained integumentary injuries of AIS score 1 with injuries to the lower extremities or head typically being AIS score 2 or greater.

A Comparison of Injuries, Crashes, and Outcomes for Pediatric Rear Occupants in Traffic Motor Vehicle Collisions

BACKGROUND This study was initiated was initiated to describe pediatric rear-occupant motor vehicle collision (MVC) injuries, including injury patterns and outcomes as well as characteristics associated with severe injury to the head and abdomen. METHODS A retrospective cohort of severely injured (Injury Severity Score [ISS] > 12) pediatric (age <18 years) patients involved in a traffic MVC as a rear occupant and treated at one of two Ontario trauma centers (2001–2010) was studied was studied. Demographic, injury, crash and outcome data were obtained from the trauma registries. Data were statistically compared by two pediatric age groups: children (0–8 years; requiring a child or booster seat) versus adolescents (9–17 years; requiring a lap-shoulder belt). RESULTS There were 36 children (34%) and 70 adolescents (66%) severely injured as rear occupants in MVCs. Despite similar ISS (p = 0.716) and mortality rates (p = 0.680) between age groups, there were significant differences in injury patterns and risk factors. Children were more likely to have severe head injuries (78% vs. 39%, p < 0.001) associated with a lack of an age-appropriate child restraints (odds ratio [OR], 3.5; 95% confidence interval [CI], 1.1–10.8; p = 0.029), middle seating (OR, 6.2; 95% CI, 1.5–26.1; p = 0.013), and side-impact crashes (p = 0.007). Adolescents were more likely to have severe abdominal injuries (23% vs. 6%, p < 0.001) associated with the use of lap-shoulder belts (OR, 3.8; 95% CI, 1.1–13.3; p = 0.034), single-vehicle MVCs (p = 0.007), and vehicle extrications (p = 0.035). CONCLUSION While safer than the front seat for children, additional study is needed on the restraint systems and the potential for injury to pediatric rear occupants in an MVC. Our data suggest that pediatric age groups differ in injuries, risk factors, and MVC impacts. Recommendations for improved protection of child occupants and preferred seating positions are required. LEVEL OF EVIDENCE Epidemiologic study, level III.

A study of injury-producing crashes on median divided highways in southwestern Ontario

The University of Western Ontario Accident Research Team investigates every fatal crash, and approximately one out of every 50 personal-injury crash, within a defined geographic area of three counties. Over a seven-year period, the team investigated 107 collisions (62 fatal and 45 personal injury) that occurred on median-divided highways. These crashes were representative of over 2,300 collisions on the highways involving 81 fatalities and injury to over 3,200 vehicle occupants. Vehicle loss of directional control prior to any impact occurred in 55 of the 62 fatal cases and in 36 of the 45 personal-injury cases. In 36 fatal cases and 17 personal-injury cases loss of control was initiated after a vehicle travelled from the roadway onto the gravel shoulder. Rollover collisions were the most frequent collision type investigated and comprised 25 fatal and 25 personal-injury cases. Unrestrained occupants made up 24 of the 29 rollover fatalities with 96% of these unrestrained occupants being ejected from the vehicle. Collision with an oncoming vehicle after median-crossover occurred in 26 fatal cases. These crashes were usually frontal or side impacts characterized by extensive vehicle damage and massive intrusion into the occupant compartment. Severe head injury (AIS 5 or greater) predominated as the cause of death in all collision types.

Skull fractures in fatalities due to motor vehicle collisions.

A retrospective analysis of 89 fatalities with skull fracture resulting from motor vehicle-pedestrian and various single passenger car frontal, side, rear and rollover collisions was done. Passenger compartment intrusion and occupant ejection were responsible for most, but not all, cranial fractures occurring in impacted motor vehicles. Victims of frontal collisions usually were unrestrained; however, a majority of individuals in cars hit by heavy trucks were wearing seatbelts. Vehicles involved in frontal crashes had crush profiles reflecting a barrier equivalent velocity (BEV) of at least 50 km/h (about 30/mph). In side impacts, most ejected occupants were unrestrained, whereas many of those intruded upon were belted. The minimum BEV calculated in these collisions approached 20 km/h (12 mph). The observation of a skull fracture integrated with accident investigation (that is, determination of head contacts) was useful in the reconstruction of various collisions. Skull fracture patterns, as documented by autopsy, reflected certain kinematic trajectories described in motor vehicle-pedestrian frontal collisions.