In the lumbar spine, the nerves course through an open tube called the spinal canal. The surrounding structures of the canal include the vertebral body, the discs at the floor of the canal and the overlying facets with their ligaments. With age the spinal canal will become smaller as these surrounding structures degenerate, enlarge and therefore encroach upon the canal space and the nerves that course through it. This closure of the canal space is termed stenosis.