Likelihood of Spinal Disc Herniations in Occupants involved in Real World Side Impacts 2020-01-0526
The prevalence of spinal disc herniations in asymptomatic individuals have been reported to increase from about 20% in those below 40 years to about 30% in those above 40 years of age. Spinal disc herniations are usually associated with degenerative changes. Though rare, they can also be caused by trauma. With an increasing number of older people on U.S. roads with a concomitant increase in the likelihood of getting involved in a vehicle collision, it is reasonable to expect that some of these occupants can present with spinal disc herniations. In this study we looked at the relationship between side impact and occupant spinal injuries, in particular disc herniations. We examined the reported occurrence of all adult spine injuries in side impact crashes in the National Automotive Sampling System - Crashworthiness Data System (NASS-CDS) database from 1993 through 2014. There were over 8,400 adult raw case occupants, corresponding to a weighted number of approximately 4.7 million, that fit the inclusion criteria. The results showed that the most common spine injury in side impact is acute muscle strain of the neck. The delta-V of a side impact is a not reliable indicator of neck strain in occupants exposed to such impacts. The total number of occupants with reported spinal disc herniations was only four; three from near-side impacts and one from far-side impact. The low prevalence in reported spinal disc herniations stands in sharp contrast to a background prevalence of 20% to 30% in asymptomatic individuals. The findings from this study suggest that there is no association between side impact and disc herniations in occupants exposed to such impacts. The lack of an association is likely due to the fact that the known experimental mechanism of traumatic disc herniation, combined hyperflexion and axial compression, is not operative in side impact.