Transient pressure gradients in the pig spinal canal during experimental whiplash motion causing membrane dysfunction in spinal ganglion nerve cells

Mechanical loading of the cervical spine during car accidents often lead to a number of neck injury symptoms with the common term Whiplash Associated Disorders (WAD). Several of these symptoms could possibly be explained by i njuries to the cervical spinal nerve root region. It was hypothesised that the changes in the inner volume of the cervical sp inal canal during neck extension-flexion motion would cause transient press ure changes in the CNS as a result of hydro-dynamic effects, and thereby me chanically load the nerve roots and cause tissue damage. To test the hypothesis, anaesthetised pigs were exposed to experimental nec k trauma in the extension, flexion and lateral flexion modes. The severity of the trauma was kept below the level where cervical fractures occur. Tran sient pressure pulses in the cervical spinal canal were duly recorded. Sign s of cell membrane dysfunction were found in the nerve cell bodies of the c ervical spinal ganglia. Ganglion injuries may explain some of the symptoms associated with soft-tissue neck injuries in car accidents. When the pig's head was pulled rearward relative to its torso to resemble a rear-end colli sion situation, it was found that ganglion injuries occurred very early on in the neck motion, at the stage when the motion changes from retraction to extension motion. Ganglion injuries did not occur when pigs were exposed t o similar static loading of the neck. This indicates that these injuries ar e a result of dynamic phenomena acid thereby further supports the pressure hypothesis. A Neck Injury Criterion (NIC) based on a theoretical model of t he pressure effects was developed. It indicated that it was the differentia l horizontal acceleration and velocity between the head and the upper torso at the point of maximum neck retraction that determined the risk of gangli on injuries.