CONSTRICTION OF THE INTERVERTEBRAL FORAMEN

The intervertebral foramen, exit of the nerve root from the spinal canal, is limited in front by the intervertebral disk and portions of the adjacent vertebral bodies. Above and below are the pedicles, while posteriorly occur the superior and inferior articular processes, with the ligamentum flavum. This opening, which is the site of movement, is normally five or six times as large as the diameter of the nerve which passes through it, thus allowing a generous reserve cushion space. Nerve foramens, not the site of movement, are only slightly larger than the nerves which traverse them. In the spine this is noted in those cases of nonsegmentation in which adjacent vertebral segments remain congenitally fused. Here the foramen is much smaller, smooth in margin and usually round or slightly oval in shape. Certain movements of the cervical and lumbar parts of the spine cause normal physiologic constriction of the foramen