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Inside Side Impact Collisions
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Side Impact (Broadside) Crashes

Broadside collisions tend to affect the middle to upper neck regions more than do frontal crashes. A recent study by Deng and Goldsmith with human replica models showed that in lateral flexion crashes, the longus capitis muscle had the greatest incidence of deformation, 57%, compared with the rest of the neck muscles. Lateral impact is complicated if and when the head strikes, or is struck by, an object such as the window or a door frame.

In side impacts, the occupant is offered little protection by either the seat back or restraint harness. The initial response of the body is lateral flexion towards the striking vehicle, with compression of the spinal structures on the struck side, and stretching of myofascial and other structures on the opposite side. The lap belt will serve as an anchor for the pelvis, reducing likelihood of ejection from the vehicle, but this actually intensifies the bending of the lumbar spine. This increases the likelihood of intervertebral disc, ligament and muscle injuries.

The patient who strikes his or her head during the collision may lose consciousness for a brief period of time. The impact to the head is, essentially, a second, separate accident. Therefore, the structures of the cervical spine are subjected to a second trauma and have almost twice the amount of post-traumatic degeneration. Hohl studied, as a subgroup, those patients who had lost consciousness during accidents; 64 percent experienced degenerative changes within the study period.

Forces incurred by striking and struck vehicles in broadside collisions are not commonly perfectly perpendicular. For example, if a broadside collision occurs between two cars in an intersection, and both are traveling at 20 mph, the actual resulting vectors of deceleration for the occupants will be oblique to the direction they are traveling in. Such oblique collisions are particularly difficult to describe. However, it is clear from studies conducted by Viano that oblique rear impact collisions hold much greater potential for injury than the pure rear-impact variety.