Spinal Stenosis

Lumbar spinal stenosis is one manifestation of the general process of spinal degeneration that occurs with aging, and often becomes symptomatic in the seventh and eighth decades of life.

Stenosis = narrowing of a hollow tubular structure.

• The central canal of the spinal column conveys the spinal cord in the cervical, thoracic and upper lumbar levels. 
• In most individuals, the spinal cord ends by the L1 level; below this level the remaining lumbar and sacral nerve roots travel as the cauda equina. 
• The nerve roots are more tolerant of chronic pressure than the spinal cord, which is why an individual may tolerate a higher degree of stenosis in the lower lumbar spine than in the cervical or thoracic region. 
• The boundaries of the central canal vary with the level of the vertebral body:
  • At the level of a vertebral body, the canal is bordered by the body itself anteriorly, the pedicles laterally, and the laminae posteriorly. This is the site that is affected in cases of congenital stenosis, where the pedicles are typically shortened. 
  • At the level of the intervertebral disc, the anterior border is formed by the annulus, the posterolateral borders by the facet joints and capsules, and the posterior border by the ligamentum flavum. These are the structures that are most affected by degenerative processes.
• The dimensions of the spinal canal and foramen are influenced by dynamic and postural factors
  • when a person rises from recumbency to standing, the resulting axial load on the intervertebral disc causes further bulging of the annulus, which in turn further compromises the central canal and the foramen. 
• The foramina decrease in size while the nerve roots increase in diameter as you move down the spine. Thus the lumbar spine is most commonly affected.