Stenosis refers to a narrowing of the spinal canal, usually in the lower back (lumbar) region. This narrowing is often a result of the normal degenerative aging process. It occurs as the disks of cartilage that separate the spine's vertebrae lose water and the space between the vertebrae become smaller, causing friction between the bones. The loss of water in the disks makes them less flexible and unable to act as shock absorbers in the spine. Daily wear and tear on the spine becomes more significant without these shock absorbers.
As the disks degenerate, vertebrae may shift, causing the spinal canal to narrow. In some cases, the nerves that travel through the spinal column to the legs become squeezed. This can cause back and leg pain, and even leg weakness. Arthritis and falls also contribute to the narrowing of the spinal canal, compressing the nerves and nerve roots and causing pain and discomfort.