- Narrowing (stenosis) of the vertebral canal may occur at single or multiple spinal levels, and mainly affects the lumbar and cervical regions.  Stenosis may affect the central canal and the 'root canals' either together or separately.  There is a developmental form of the condition which mainly affects the central canal, but more commonly the stenosis is degenerative, and results from intervertebral disc narrowing and osteoarthritic changes in the facet joints.  This latter combination is more likely to narrow the intervertebral foramen and the 'root canal', even though the sectional profile of the vertebral canal in the affected lumbar vertebrae typically changes from the shape of a bell to that of a trefoil.  The lumbosacral intervertebral foramen, which is normally the smallest in the region, is particularly liable to such stenosis.

- Severe spinal stenosis may compress the spinal cord and compromise its arterial supply.  More localized 'root canal' stenosis will present with the clinical features of spinal nerve compression, but without the tension signs which characterize the stretching of nerve roots over a prolapsed disc.  Ischaemia of the nerves and roots may be more responsible for the damage than is the actual physical compression of the neural tissue.