Neck injuries caused by swift extension-flexion motions of the cervical spine during car collisions result in human suffering and high societal costs. The symptoms of these patients are well documented but the actual site of the injury as well as the relation between this injury and the head-neck motion have not been established.

In earlier work by our group, experimental extension-flexion trauma to the neck of pigs has revealed signs of injury to the spinal ganglia that could explain many of the typical symptoms. As a part of that work, transient pressure changes were measured in the cervical spinal canal. An hypothesis, that such pressure changes would be the cause of the ganglion injuries was presented.

The present paper focuses on when, during the extension-flexion motion, this injury may occur and what neck motion parameters may be of relevance.

A mathematical model, based on Navier Stokes equations, was developed and validated against experimental data. The model predicts the pressure changes in the spinal canal as a function of the volume change inside the canal during neck bending in the x-z (sagittal) plane.

Further experiments on pigs were conducted. Preliminary results indicate that ganglion injuries, as well as pressure transients inside the spinal canal, seem to correlate to the phase shift when the neck passes an s-shape (or maximal retraction) during the rearward motion of the head. That is, when the upper neck quickly changes from a flexion to an extension shape. Static loading of the neck resulted in no signs of injuries to the ganglia.

With these findings established we present a possible candidate for a neck injury criterion. The criterion is based on the relative acceleration between the top and the bottom of the cervical spine. We also discuss a tolerance level based on the pig tests.