The intervertebral disks act as “shock absorbers” between the vertebral bodies and are responsible for flexibility of the spine. Each consists of a pulpy nucleus contained in an outer fibro cartilaginous ring. The disk cannot “slip” but the soft nucleus may herniate through the outer ring, producing a bulge forward or sideways into the spinal canal. Usually this is due to trauma (80 percent of cases) associated with changes in the fibrous consistency of the disk’s outer wall. Typically, the disk “slips” while the person is lifting a heavy weight with the body bent. (The risk of a disk injury can be reduced by keeping the back straight while lifting.) This condition, known technically as herniated disk, ruptured disk or prolapsed disk, occurs most often in persons in their 30s and 40s.

Protrusions of the lumbar disks (in the lower part of the back) are approximately fifteen times more common than cervical protrusions (in the neck); thoracic disks (in the chest region) rarely are affected. Protrusion backward may impinge on the spinal cord or the nerves leading from it, causing pain (sciatica), weakness, and numbness, especially in a leg.

X-ray examination of the spinal area usually will show loss of disk space between particular vertebral bodies; it will not show the disk itself. Injection of a radiopaque dye (a myelogram) is required to define the precise extent of a disk’s backward protrusion. Treatment depends largely on the severity of the symptoms and the nature of the injury.

The first treatment for slipped disk is for the person to rest in bed, lying on a firm mattress supported on a wooden base. Complete rest often leads to relief of symptoms within a few days and to healing within a few weeks. If the rest alone is ineffective, then the bones of the spine may be stretched apart by traction, under medical supervision.

Persons who have experienced a slipped disk are at higher risk for developing more, either in the same spot or elsewhere. Treatment is aimed at controlling pain and enabling the person to continue to work, but it is not a cure. If these measures fail, or if the symptoms recur on several occasions, then surgical treatment may be necessary to remove the protruded section of disk.