Time, pressure take their toll on spinal disks


June 07, 1994|By Simeon Margolis, M.D. | Simeon Margolis, M.D.,Special to The Sun

Q: I have had lower back pain on and off many years. Last month, the pain spread into my left leg, and my doctor told me I have a slipped disk. The pain is almost gone after bed rest, but I would like to know what is meant by a slipped disk and whether surgery will be necessary.

A: Between the bones of your spine are disks that act as shock absorbers. They are flat pads, about 1 3/4 -inch thick, with a ring of tough connective tissue (cartilage) covering a soft jellylike center called the nucleus pulposus. Disks in the lower back (lumbar spine) wear out early because they are subjected to large amounts of pressure called loads.

After years of bearing such loads, disk centers slowly lose water and dry out. As a result, even minor injury or strain can cause the nucleus pulposus to squeeze out or herniate through the outer connective tissue of a weakened disk. "Slipped disk" is a misnomer; the disk does not slip so much as protrude.

A herniated disk may cause only low back pain and muscle spasms. However, it often irritates nerve roots as they leave the spinal cord and cause sciatica pain, radiating into the buttocks and down the legs, at times to below the knees and into the calves and feet. Loss of muscle strength in the legs may also result. Pressure on the nerves may lead to the sudden onset of impaired bowel function and an inability to urinate.

About 80 percent of patients with herniated lumbar disk will repond to treatment with bed rest and pain medication. One possible advantage of surgery is that it may bring improvement more rapidly than conservative treatment.

Some of the indications for surgery include impaired bowel or bladder function, persisting or increasing sciatica despite bed rest, progressive weakness and recurring episodes of incapacitating sciatic pain.

Dr. Margolis is professor of medicine and biological chemistry at Johns Hopkins School of Medicine.

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