Causes

The backbone (spine) runs from your neck to your lower back. The bones of your spine form a spinal canal, which protects your spinal cord (nerves).

Some people are born with a small spinal canal. But most spinal stenosis occurs when something happens to narrow the open space within the spine. Causes of spinal stenosis may include:

• Overgrowth of bone. Wear and tear damage from osteoarthritis on your spinal bones can prompt the formation of bone spurs, which can grow into the spinal canal. Paget's disease, a bone disease that usually affects adults, also can cause bone overgrowth in the spine.
• Herniated disks. The soft cushions that act as shock absorbers between your vertebrae tend to dry out with age. Cracks in a disk's exterior may allow some of the soft inner material to escape and press on the spinal cord or nerves.
• Thickened ligaments. The tough cords that help hold the bones of your spine together can become stiff and thickened over time. These thickened ligaments can bulge into the spinal canal.
• Tumors. Abnormal growths can form inside the spinal cord, within the membranes that cover the spinal cord or in the space between the spinal cord and vertebrae. These are uncommon and identifiable on spine imaging with an MRI or CT.
• Spinal injuries. Car accidents and other trauma can cause dislocations or fractures of one or more vertebrae. Displaced bone from a spinal fracture may damage the contents of the spinal canal. Swelling of nearby tissue immediately after back surgery also can put pressure on the spinal cord or nerves.