There is evidence of nerve compression at the level of the intervertebral foramen (IVF) occurring anywhere from 15.4% to 78% of levels inspected. Most of the spines inspected were already prescreened to eliminate those that were definitely known to have nerve compression problems. Pressures as little as 10 mm Hg can alter the nerve root and dorsal root ganglion’s abilities to function normally. In the normal range of motion the pressures generated in the IVF may exceed 30 mm Hg. When considering the concept of a joint fixated in a diminished sphere of its normal range of motion in conjunction with the mild pressure increases, it becomes apparent that nerve function can be significantly altered. 

The chiropractic adjustment can effect a restoration of normal H-reflex in compressed nerve roots without altering the H-reflex at uninvolved levels. The major variables of compression are the rate of onset, the amount of pressure generated, and the time maintained. Another major variable in the recovery is age. The younger the nerve tissue the better chance for a full recovery. The concept that a vertebral subluxation can induce pressure increases at the level of the IVF is supported by the literature. This increase, though seemingly mild, is enough to alter nerve function. The garden hose theory or hard bone - soft nerve explanation of vertebral subluxation is considered by some to be archaic but appears to be a valid entity at least in the lower cervical spine. More research is needed to decipher the susceptibility to mild pressure increases throughout the spine.

Key Words: Spinal nerve root, compression, dorsal root ganglia, chiropractic, adjustment, vertebral subluxation, manipulation