Figure 1.

Schematic axial representation of the degenerative changes to the lumbar spine. Narrowing of the spinal canal (red) develops subsequent to disk protrusion (blue), hypertrophy of the facet joints (gray), and hypertrophy or folding in of the ligamentum flavum (yellow). Depending on the location of the changes, the lateral recess and/or neuroforamina may also undergo narrowing (orange). Lumbar olisthesis or instability can also result in a narrowing of the spinal canal and especially the neuroforamina.