Vehicle Rear Impacts and Spinal Disc Herniations in Occupants: Is there a Basis for Causation? 2017-01-1458

Disc herniations in the spine are commonly associated with degenerative changes, and the prevalence increases with increasing age. With increasing number of older people on U.S. roads, we can expect an increase in clinical findings of disc herniations in occupants involved in rear impacts. Whether these findings suggest a causal relationship is the subject of this study. We examined the reported occurrence of all spine injuries in the National Automotive Sampling System - Crashworthiness Data System (NASS-CDS) database from 1993 to 2014. There were over 4,000 occupants that fit the inclusion criteria. The findings in this study showed that, in the weighted data of 2.9 million occupants, the most common spine injury is an acute muscle strain of the neck, followed by strain of the low back. The delta-V of a rear impact is a reliable indicator of the rate of acute cervical strain in occupants exposed to such impacts. The number of disc herniations was small in all three segments of the spine: five in the neck, none in the thoracic spine, and two in the lumbar spine for the 4,348 raw cases, compared to a background prevalence of 20 to 30 % disc abnormalities in asymptomatic individuals. Kinematic analyses of human volunteers, post-mortem human subjects (PMHS) and anthropomorphic test devices (ATDs) from other studies show that the known experimental mechanism of causing a traumatic lumbar disc herniation by hyperflexion and axial compression is not operative during a rear impact. Taken together, the findings from the real world data in this study, the occupant kinematic analyses from other studies in conjunction with the known experimental mechanism to produce a traumatic disc herniation all appear to support the hypothesis that there is a lack of a causal link between rear impacts and traumatic disc herniations in the spine.