Likelihood of Spinal Disc Herniations in Occupants Involved in Real World Side Impacts

The prevalence of spinal disc herniations in people with no spinal symptoms have been reported to increase with age; from about 20% in those below 40 years to about 30% in those above 40 years. Spinal disc herniations are usually associated with degenerative changes. Though rare, spinal disc herniations can also be caused by trauma. With an increasing number of older people on U.S. roads with a concomitant increase in the probability of getting injured in a vehicle collision, it is reasonable to expect that some of these occupants can present with clinical findings of spinal disc herniations after a side impact, and attribute these findings to the impact. In this study, we looked at the relationship between real world side impacts and the occurrence of spinal injuries, in particular disc herniations, in occupants involved in such impacts. We examined the reported occurrence of all 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 cervical spine, followed by acute muscle strain of the lumbar spine. The total number of occupants with reported spinal disc herniations was only three; all from near-side impacts. The low prevalence of reported spinal disc herniations stands in sharp contrast to a background prevalence of 20% to 30% in asymptomatic individuals. The findings from the real world data in this study, in light of known spinal responses in experiments conducted on post-mortem human subjects (PMHSs) and anthropomorphic test devices (ATDs) exposed to near- and far-side impacts, suggest that side impacts do not present a mechanism of traumatic disc herniation.