Risk Factors of Whiplash, Occupant Position

Having one’s head turned at the
moment of a rear impact is a known
risk factor for injury. The combination
of head rotation and rapid extension
reates tremendous strain on the
ligaments and nerves of the neck.

Of the many risk factors that increase the chance of whiplash injury, having one’s head turned at the time of the collision is one that has been recognized since the mid 1990s. In 1994, a group of Swiss researchers¹ found that turned head position was the leading predictor of long-term whiplash pain:

“They reported that radicular deficits and associated radiculopathy were most frequently documented in individuals whose heads were rotated at the time of rear impact and that after 1 year the symptoms significantly worsened.” ²

A few recent studies have examined the issue of spinal nerve ganglion injury. This research is based on the theory that during a whiplash motion, the ganglion is crushed or compressed, injuring the nerve bundle. This injury can then, in turn, result in chronic pain. The earlier studies have indeed found that this compression can occur, but no studies have looked at the issue of turned head position. Now a new team of researchers from Yale has done exactly that.

In this study,³ the authors prepared six human cadaver spines and performed test collisions with them in which the specimens were rotated slightly as if looking to one side. The specimens were subjected to impacts ranging from 2g to 8g of acceleration. They then compared their findings to previous findings on forward head position.

• The authors found significant pinching of the ganglion at C5-C6 and C6-C7 at the highest acceleration when compared to the baseline, 2g acceleration. This is also the area of the spine most likely to be injured in a rear end collision.
• Turned head position significantly increased the risk of compression of the spinal nerve ganglion, when compared to straight-forward head position.
• If the spine has pre-existing degenerative changes, the areas of risk increase to C3 and C4.

The authors state that injury to the spinal nerve ganglion can cause pain in at least two different ways:

• The nerves of the ganglion can become sensitized when compressed, causing pain signals in that spinal root.
• A rear end collision with the occupant’s head turned can result in cervical ligament injury and instability, leading to further, repeated injury to the ganglion. This could in turn result in repeated pain signals being sent to the brain.

From this study and others, it is clear that the spinal nerve roots are at risk of injury during rear end collisions. It is important when dealing with whiplash patients to take a thorough history to determine head position at the time of the crash.

1. Sturzenegger M, DiStefano G, Radanov BP, Schnidrig A. Presenting symptoms and signs after whiplash injury: the influence of accident mechanisms. Neurology 1994;44:688-693.
2. Tominaga Y, Maak TG, Ivancic PC, et al. Head-turned rear impact causing dynamic cervical intervertebral foramen narrowing: implications for ganglion and nerve root injury. Journal of Neurosurgery: Spine 2006;4:380-387.
3. Slipman CW, Plastaras CT, Palmitier RA, et al. Symptom provocation of fluoroscopically guided cervical nerve root stimulation. Are dynatomal maps identical to dermatomal maps? Spine 1998;23:2235-2242.