Can a concussion be caused by a low-speed rear-end crash? The prevailing science suggests the answer is no, but new research* has identified some cases where the answer could be yes.
Most people link whiplash injuries to low-speed rear-end crashes and concussions to direct head impacts. These links are sufficiently pervasive that the type of impact—rear-end crash versus a direct head impact—may influence a clinical diagnosis for what can be a similar pattern of symptoms. From a biomechanical perspective, rear-end crashes generate head impacts with the head restraint and direct head impacts generate forces in the neck, which mean that mechanisms for both whiplash injury and concussion often co-exist.
To answer the question of whether a concussion can occur in a low-speed rear-end crash, we compared how a computer model of the brain responds during sport-related head impacts to how it responds during head restraint impacts that occur in rear-end crashes.
We used head impact data from football and rear-end crash tests as input to the brain model and then examined the resulting brain strain, i.e., how much the brain stretches and distorts. We then compared these results to data from concussed NFL players whose head impacts were reconstructed from game video, and in particular to two players whose impacts were to the back of the head, the region of the head that strikes the head restraint. We found that football impacts caused higher brain strains than most of the rear-end crash tests we examined, but there were some instances where both types of impacts produced similar amounts of strain in the brain. In one crash involving a 15 km/h speed change and a low head restraint, the dummy’s head wrapped onto the top of the head restraint and caused similar brain strains to head impacts that were more severe than the two responsible for concussions in NFL players.
Figure - Two images of the peak strains on the brain’s surface as calculated by the SIMon brain model. The left image shows the largest brain strains produced by a rear-end collision, which consisted of a 15 km/h (9 mph) vehicle speed change with a low head restraint. The right image shows the largest brain strains produced during a low rear football impact, which simulated a helmeted head impact with a closing speed of 33 km/h (21 mph). The simulated football impact was more severe than two low rear impacts that have caused concussions in NFL players.
These findings show that brain strains associated with some concussions can occur during rear-end crashes in some special cases. They also show that most exposures to rear-end crashes probably don’t generate the amount of brain strain associated with concussion. For clinicians, our findings mean that they should not rule out a concussion just because their patient experienced a rear-end car crash, particularly if the engineering analysis indicates a higher speed change combined with a poorly positioned head restraint.
* Elkin BS, Elliott JM, Siegmund GP (2016). Whiplash injury or concussion? A possible explanation for concussion symptoms in some individuals following a rear-end collision. Journal of Orthopaedic & Sports Physical Therapy 46(10):874-85.