The most common cause of lumbar spinal stenosis is age-related changes of the spine. These changes include thickening of soft tissues and a gradual deterioration of spinal discs and joints that connect the spine's vertebrae. Any of these conditions can narrow the spinal canal. Spinal stenosis usually develops gradually and may begin to squeeze the spinal cord or its nerve roots.

Age-related degeneration often occurs in association with certain disorders:

• Osteoarthritis of the spine wears away joint cartilage and causes bony growths (spurs).
• Certain bone diseases, such as Paget's disease, fluorosis, and diffuse idiopathic skeletal hyperostosis, may soften the spinal bones or cause too much bone to grow.

Other conditions that may cause spinal stenosis include:

• An abnormally narrow spinal canal, which can be an inherited condition.
• Spondylolysis, which is a defect or fracture on one or both of the wing-shaped parts of a vertebra. A vertebra may slide forward or backward over the bone below and may squeeze the spinal cord or a nerve root.
• Spinal fracture.