Anatomy of the intervertebral foramen.

The intervertebral foramen serves as the doorway between the spinal canal and periphery. It lies between the pedicles of neighboring vertebrae at all levels in the spine. A number of categorization schemes have been attempted to describe the boundaries of the intervertebral foramen. No uniform agreement has been made on which classification best describes this area. Studies of the nerve root canals have clearly noted variations in the angle of take-off from the thecal sac, length of the nerve root, and placement of the dorsal root ganglion from different lumbar levels. The nerve root canal receives a dual blood supply from central and peripheral sources. The dorsal root ganglion also has a dual vascular supply that aids in preventing damage to this vital foraminal structure. The presence of ligamentous structures within the foramen has been demonstrated by a number of recent studies. These ligaments serve a protective and organizational role for the neurovascular structures of the foramen. A thorough knowledge of the intervertebral foramen will allow the understanding of the pathological and degenerative changes that cause compression or injury to these foraminal structures.