Spinal stenosis is a narrowing of the spinal canal, which reduces the space available for the spinal cord and the nerves that branch out from it. The narrowing most often occurs in the lower neck or lower back as part of age-related changes in the spine, also known as osteoarthritis. The cause may be thickening of bones, ligaments, joint capsules, or small bulges on the discs (the cushions between the vertebrae). If the pressure is caused by a bulging disc, it is called a herniated disc.

The spinal cord lies protected within the spinal canal, from which nerves branch out to the rest of the body. When the canal becomes too narrow, pressure may be placed on the spinal cord or nerve roots.

The symptoms depend on where the narrowing is located. In the lower back, it typically causes pain, sensory disturbances, or heaviness in the legs, which worsen when walking or standing and are relieved by bending forward or sitting down. The pain may radiate into the legs, and some people experience accompanying back pain or muscle weakness. In severe cases, urination, bowel movements, or sensation in the groin may be affected.

If the narrowing is in the neck, it can cause reduced strength and sensory disturbances in the arms and, in more severe cases, also in the legs, which can lead to difficulty walking. In rare cases, the bladder and bowel may be affected. The condition usually develops slowly, but the symptoms do not always worsen. In some people, they disappear completely or lessen over a few years, while others experience persistent symptoms for a longer period.

Spinal stenosis occurs in both men and women, most often after the age of 50–60. The majority are over 70 when diagnosed. Hereditary factors may play a role, while physical strain has only limited significance.