The most common reason behind the development of spinal stenosis is degenerative arthritis, or bony and soft tissue changes that occur because of ageing. Spinal stenosis is usually found in the patients who are over 50 years of age, and becomes progressively more severe with increase in age. The normal "wear and tear" of ageing that can cause arthritis in the spine that leads to spinal stenosis. This can be from bone spurs forming, bulging and wear of the intervertebral discs, and thickening of the ligaments between the vertebrae.
Sometimes, increased motion between the vertebrae can cause one vertebra to slip forward on another. This is called spondylolisthesis, and it can also cause spinal stenosis.