Pain in the back may be caused by strain on muscles or a "slipped" intervertebral disk, or it may be affiliated with some type of disorder of the bones and parts of the spinal column.

The twenty-four vertebrae that make up the spinal column (seven cervical, twelve thoracic, and five lumbar) extend from the base of the skull to the sacrum, the triangular "centerpiece" of the pelvis. The vertebrae are separated by pads of tough, elastic cartilage---the intervertebral disks---which give the spine its flexibility and also act as shock absorbers. The bones are also bound together by strong ligaments and by several groups of powerful muscles that run mainly in two bands on either side of the backbone. The spine acts as the central girder of the skeleton; it also provides a protective tunnel for the spinal cord (which reaches from the brain down to the level of the second lumbar vertebra) and the nerves that branch from it.

Most commonly, backache is caused by strain of the muscles around the lower part of the spine. This may be due to unaccustomed exercise---a weekend spent shoveling snow, for example---or to sitting for prolonged periods in an incorrect posture. Strain on the spine is least when the back is straight; a chair that forces the spine into a curve is likely to provoke chronic back strain.

A separate, acutely painful type of backache also originating in the muscles is lumbago. Here the pain often is localized to one extremely painful spot in the muscles, usually in the lower lumbar region and slightly to one side of the midline. Lumbago is often experienced after a combination of unaccustomed exercise and cold---digging the garden in spring, for example---and may be severe enough for the victim to be unable to move out of bed. The cause is believed to be spasm of a group of muscle fibers. Even with no treatment other than rest and simple pain-relieving drugs, such as aspirin, the condition resolves within a few days; in some cases recovery may be hastened by injection of a mixture of a local anesthetic and steroid drug into the "trigger spot."

The second common cause of sudden severe backache is damage to one of the intervertebral disks in the lumbar region of the spine. Damage is most likely to occur when the person is lifting a heavy weight while his back is curved. Pressure on the disk, which consists of a tough capsule with a soft, elastic center, may rupture the capsule and allow part of the central nucleus to protrude. If this protrusion extends into the spinal canal it may press on one of the spinal nerves or even on the spinal cord. Typically, this pressure causes pain extending down the main sciatic nerve, which runs from the buttocks to the foot. The pain is made worse by coughing, straining, or bending the back. If the symptoms persist there may also be loss of feeling in the foot or lower part of the leg and some muscular weakness.

The basic treatment of prolapsed disk (or "slipped disk") is rest, with the person lying flat on his back in bed. Rest for two weeks, sometimes more, often allows the disk to reabsorb the protrusion and the damaged capsule to heal. If the symptoms from pressure on the spinal nerves are severe, or if they do not resolve with simple rest, traction may be added: Weights are attached to the legs to lengthen the spine, thus pulling the vertebrae apart and promoting return of the disk to its normal condition. The most radical treatment, which may be necessary if the prolapse, is surgical excision of the damaged portion of the disk.

Unfortunately, anyone who has suffered a prolapsed disk is at risk of recurrence; once the acute symptoms have settled, some program of preventative treatment is important. This will include exercises to strengthen the muscles that support the spine and instruction on posture and the safe, correct way to lift weights, tie one's shoes, and perform other simple daily activities. Sometimes a physician may advise the wearing of a protective and supporting corset.

The third common cause of sudden backache is a minor displacement of one vertebra relative to its neighbors. Just how frequently this problem occurs is a matter of dispute within the medical profession. Some physicians (and all osteopaths and chiropractors) believe that most episodes of backache can be relieved by manipulation of the spine, thus encouraging the bones to return to their normal alignment. Without a doubt, spinal manipulation often does relieve symptoms, but reliance on this method can be dangerous if the pain is due to one of the rarer causes of backache, such as a tumor or an infection such as tuberculosis.

Chronic backache may be caused also by arthritis of the spinal joints. Ankylosing Spondylitis is a severe form of spinal arthritis, especially common in young men and related to Rheumatoid Arthritis, which may also affect the spine; both diseases cause progressive pain and stiffness of the spine. The common degenerative Osteoarthriitis also affects the spine; most people over the age of 50 have some stiffness of the back from minor arthritic changes. No specific treatment is needed for this form of arthritis unless symptoms develop.

Among the many other causes of backache are infections (tuberculosis was especially common in the last century and is still a major problem in developing countries), tumors of the bones and of the spinal cord and nerves, and the metastasis (spread) of cancer cells to the spine. For that reason, full investigation---including X-ray studies of the spine and blood tests---is needed before treatment is given in any case in which the cause of the pain is not obvious.

Most episodes of backache are preventable: With correct posture, care in lifting weights, and regular exercise to maintain muscle tone, the joints in the back should remain as trouble-free as those elsewhere in the body.

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