What is Spinal Stenosis?

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The spine is a column of 26 bones that extend in a line from the base of the skull to the pelvis. Twenty-four of the bones are called vertebrae. The vertebrae link to each other and are cushioned by shock-absorbing disks that lie between them.

Spinal stenosis is a narrowing of spaces in the spine (backbone) that results in pressure on the spinal cord and/or nerve roots. This disorder usually involves the narrowing of one or more of three areas of the spine:

1. the canal in the center of the column of bones (vertebral or spinal column) through which the spinal cord and nerve roots run,
2. the canals at the base or roots of nerves branching out from the spinal cord, or
3. the openings between vertebrae (bones of the spine) through which nerves leave the spine and go to other parts of the body.

The narrowing may involve a small or large area of the spine. Pressure on the lower part of the spinal cord or on nerve roots branching out from that area may give rise to pain or numbness in the legs. Pressure on the upper part of the spinal cord (that is, the neck area) may produce similar symptoms in the shoulders, or even the legs.

Who gets spinal stenosis?
This disorder is most common in people over 50 years of age. However, it may occur in younger people who are born with a narrowing of the spinal canal or who suffer an injury to the spine.

What causes spinal stenosis?
Inherited condition: Some people inherit a small spinal canal or have a curvature of the spine (scoliosis) that produces pressure on nerves and soft tissue and compresses or stretches ligaments. In an inherited condition called achondroplasia, defective bone formation results in abnormally short and thickened pedicles that reduce the diameter of (distance across) the spinal canal.

Acquired conditions that can cause spinal stenosis include aging, tumors and trauma to the spine.

Aging & osteoarthritis
Spinal stenosis most often results from a gradual, degenerative aging process. Either structural changes or inflammation can begin the process. As people age, the ligaments of the spine may thicken and calcify (harden from deposits of calcium salts). Bones and joints may also enlarge, and osteophytes (bone spurs) may form. When the health of one part of the spine fails, it usually places increased stress on other parts of the spine.

Aging with secondary changes is the most common cause of spinal stenosis. Two forms of arthritis that may affect the spine are osteoarthritis and rheumatoid arthritis.

Spondylolysthesis, a condition in which one vertebra slips forward on another, may result from a degenerative condition or an accident, or may be acquired at birth. Poor alignment of the spinal column when a vertebra slips forward onto the one below it can place pressure on the spinal cord or nerve roots at that place.

Tumors of the spine
Tumors of the spine are abnormal growths of soft tissue that may affect the spinal canal directly by inflammation or by growth of tissue into the canal. Tissue growth may lead to bone resorption (bone loss due to overactivity of certain bone cells) or displacement of bone and the eventual collapse of the supporting framework of the vertebral column.

Accidents
Trauma (accidents) may either dislocate the spine and the spinal canal or cause burst fractures that produce fragments of bone that penetrate the canal.

Although surgery that involves fusion (union) of vertebrae may be skillfully performed, tissue swelling after surgery may place pressure on the spinal cord.

What are the symptoms?
Spaces within the spine can narrow without producing any symptoms. However, if narrowing places pressure on the spinal cord or nerve roots, there may be a slow onset and progression of symptoms. The back itself may or may not hurt.

Most often, people experience numbness, weakness, cramping, or general pain in the legs that occurs during flexing the lower back while sitting. (The flex position "opens up" the spinal column, enlarging the spaces between vertebrae at the back of the spine.) If a disk between vertebrae is compressed, people may feel pain radiating down the leg (sciatica).

People with more severe stenosis may experience abnormal bowel and bladder function and foot disorders. In very rare instances, compression results in partial or complete paralysis of the legs.

If you are experiencing any of the symptoms of spinal stenosis, find a physician who specializes in spinal conditions. Read what orthopaedic surgeon James Stoll, M.D., with Columbia St. Mary's, has to say about the pros and cons of back surgery.

Source: National Institutes of Health (NAMSIC/National Institutes of Health)
1 AMS Circle
Bethesda, Maryland 20892-3675, and on the NIAMS Web site at
http://www.nih.gov/niams/healthinfo/