While some people are born with a small spinal canal, most spinal stenosis occurs when something happens to reduce the amount of space available within the spine. Causes of spinal stenosis may include:
Overgrowth of bone. Wear and tear 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 thick over time. These thicker 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.
Spinal injuries. Car accidents and other major 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 adjacent tissue immediately following back surgery also can put pressure on the spinal cord or nerves.