Brainstem injury in motor vehicle crashes

This is a descriptive study of the frequency and risk for brainstem injury by crash type, belt use, and crash severity (delta-V). NASS-CDS electronic cases were reviewed to see whether the transition from vehicles without advanced airbags and seat belts and side airbags and curtains to vehicles with the safety technologies has influenced the risk for brainstem injury.

1994-2013 NASS-CDS was analyzed to determine the number of brainstem injuries in nonejected adults (15+ years old) in vehicle crashes. Crashes were grouped by front, side, rear, and rollover. The effect of belt use was investigated. Light vehicles were included with model year (MY) 1994+. Occupants with severe head injury (Abbreviated Injury Scale [AIS] 4+) and Maximum Abbreviated Injury Scale (MAIS) 4+F injury were also determined. The risk for injury with standard errors was determined using the MAIS 0+F exposure by belt use and crash type. NASS-CDS electronic cases were studied with brainstem injury in 2001-2013 MY vehicles.

NASS-CDS indicates there are 872 ± 133 cases of brainstem injury per year. About 16.0% of AIS 4+ head injury involves the brainstem. For belted occupants, the highest risk for brainstem injury was in side impacts at 0.065 ± 0.010%. In contrast, the highest risk for brainstem injury was 0.310 ± 0.291% in rear impacts and 0.310 ± 0.170% in rollovers for unbelted occupants. The risk for brainstem injury increased with crash severity. The highest risk for brainstem injury was 3.54 ± 1.45% in crashes with >72 km/h (>45 mph) delta-V. Exponential functions fit the change in risk with delta-V. Eighteen NASS-CDS electronic cases showed that brainstem injury occurred in very severe collisions where the occupant experienced multiple injuries from intrusion or impact on vehicle structures stiffened by deformation.

The risk for brainstem injury in belted occupants has remained essentially constant over 20 years, whereas the risk for MAIS 4+F injury has declined 38.3%. The prevention of brainstem injuries must address the extreme speed of collisions and weight mismatches that overwhelm structures, seat belts, frontal airbags, side airbags, and curtains in modern vehicles.