Like most other injuries, concussions occur in the blink of an eye. Unlike most injuries, however, concussions can occur without leaving a physical mark.
Even when a concussion is diagnosed, the question may remain whether the event alleged to have caused the concussion was indeed responsible. From a biomechanical perspective, it is sometimes possible to confirm or refute causation.
Concussions require that the head experience sufficient trauma to transiently affect brain function. To determine whether a traumatic event had the potential to cause a concussion requires a reconstruction of the event to characterize and quantify the type and magnitude of forces that were applied to the head. The applied forces are then compared to the forces that cause concussion. These forces are often quantified as linear acceleration (reported in units of gravitational force, g) and rotational acceleration (in units of radians per second2).
Physical evidence such as external trauma to the head (e.g., lacerations or extracranial swelling), damage to contacting structures (e.g., a dent in a wall or vehicle hood), and overall scene geometry (e.g., dimensions of a staircase or vehicle interior measurements) can be used to reconstruct a head impact. Witness evidence can also be used to estimate factors such as posture, pre-impact activity and relevant environmental variables. Data from scientific studies of instrumented surrogate headforms (dummies) or cadavers are used to estimate the forces applied during the impact. If published data are not available, then case-specific tests can be performed to estimate the head impact exposure.
Recently, head impact exposure and concussion incidence have been characterized through reconstruction and in situ measurements of head accelerations in professional, collegiate, high school, and youth sports. Although most head impacts do not generate concussions, biomechanical risk curves have been developed from impacts that have caused concussion. These data are analogous to the introduction of “black boxes” in motor vehicles that provided the first real-world data on the relationship between collision exposure and whiplash injury. Similar to whiplash, the percentage of individuals that sustain a concussion is low compared to the number of exposures, so it is important to understand that exposure to forces above concussion thresholds is necessary but not sufficient to cause a concussion. Armed with threshold data, the possibility that a particular traumatic event was capable of causing a concussion can be evaluated.
At MEA Forensic we have the biomechanical expertise required to perform this analysis and help confirm or refute a causal link between a diagnosed concussion and a specific event.