Lumbar Intervertebral Disc Injuries in Low Velocity Rear End Vehicular Collisions: The Current Evidence

Rear-end collisions are the most frequently occurring type of collision in the United States, accounting for approximately 29% of all collisions. Of these collisions, many are socalled “low velocity” or “minimal impact” type collisions, characterized by low impact speeds (less than 9-10 mph) and limited observable damage to the rearended vehicle. Lumbar intervertebral disc injuries are sometimes claimed by injured parties as a result of such collisions. This paper addresses lumbar biomechanics and relevant topics, such as degeneration and potential injury mechanisms, with a focus of how such knowledge relates to the occurrence of lumbar intervertebral disc injuries as a result of low velocity rear-end impacts. We conclude that the evidence for the occurrence for lumbar disc injuries in such collisions is not compelling, reflecting limited impact forces, limited lumbar range of motion, and the general lack of injury mechanisms being present. However, it is acknowledged there are significant data gaps. Important questions needing further inquiry include the experimental validation of the concept that acute disc injuries can occur at all under such conditions and the role of degenerative processes. Central Gonzalez-Blohm et al. (2014) Email: Ann Orthop Rheumatol 2(4): 1036 (2014) 2/10 between a lumbar disc injury diagnosis and a recent vehicular collision is often the result of “diagnosis by history” (i.e. the treatment provider is relying strictly on the history as reported by the injured party). Alternatively, the causal relationship results from a “diagnosis of exclusion” (i.e. there is no obvious injurious event to reference other than the recent collision). Secondary monetary gains often exaggerate or muddle the medical issue as patients, physicians and attorneys may financially benefit from insurance settlements. Also, physicians who provide treatment under a financial arrangement, such as a Letter of Protection (LOP), now could have a vested interest in the outcome of the case; hence they may not be unbiased in their testimony. The public widely assumes, based on the medical causation approach (diagnosis by history and exclusion), an underling assumption that pain or abnormalities after an event must originate from the event and does not derive from a preexisting condition. Two theories related to the “acute event causes injury” exist. The first postulates that an acute event such as a vehicular collision can establish lumbar disc injury in otherwise healthy subjects. The second hypothesizes that the subject already has some stage of disc pathology, but is otherwise asymptomatic, and the acute event is the final step in the transition from asymptomatic to symptomatic; many refer to this as the “egg shell theory”. Advocates to the second theory note that such condition is more likely in older subjects, i.e., and they expect that degenerative changes would be present. Regardless of the injury theory, many involved parties claim these injuries after low impact rear end collisions, but the feasibility of this event is ambiguous. This investigation reviews background information and scientific evidence available in the area of lumbar intervertebral disc injuries related to low velocity rear-end collisions. Literature related to the question as to whether an acute lumbar disc injury can occur at all is discussed, as well as the importance of exploring any data gap.