The most common is degenerative, occurring in essentially the entire population with age, to varying degrees and with varying clinical significance. This degenerative narrowing is referred to as spondylosis . Again, spondylolisthesis can have many causes, most commonly degenerative and traumatic. As the reader may guess, spondylolysis can have several causes. These include degeneration, trauma, and congenital defects.
Several factors contribute to the narrowing of the spinal canal with degenerative changes.
This may be analogous to degeneration and swelling of other joints in the body. Second, the major ligament of the spinal canal, the ligamentum flavum , undergoes hypertrophy and buckling. Third, the intervertebral discs may bulge posteriorly into the canal or herniate. Fourth, as mentioned above, the vertebrae may slip forward. Finally, these changes may be superimposed on a congenitally narrow canal.