The narrowing of the channel that houses the spinal cord or openings for the nerve roots. The most common sites of spinal stenosis are the neck (cervical) or the low back (lumbar). However, spinal stenosis can occur anywhere along the spine. The most common cause is arthritis, but the exact cause of narrowing and the natural history of the condition are still poorly understood. Most patients with spinal stenosis are in their sixties and seventies or older, but there are some conditions that cause it in younger people too. Treatment is either medical (pain relief, physical therapy) or surgical. There is still controversy over which treatment is most effective.