What is a disk?

The spine is a column that comprises bones, disks and ligaments. The vertebrae provide the anterior support and structure of the spine. The disks are between the bones, and they are shock absorbers between the vertebrae. The disks also contribute to the flexibility and mobility of the spinal column. The disks comprise two parts:

• The inner portion of the disk is a jellylike material called the nucleus pulposus.
• The outer part of the disk, called the annulus fibrosis, is stronger and more fibrous. The annulus fibrosis surrounds and supports the inner jelly material. The annulus is rich in nerve fibers, especially the back portion, and may contribute to discogenic back pain.

Disk material is mostly composed of water and other proteins. The water content gradually reduces as a normal part of aging. This can cause the disk to flatten and develop tears or cracks throughout the annulus fibrosis. This condition often is called a "degenerative disk," and it may cause pain.

With a degenerative disk, the inner jelly material can bulge out and press against the annulus fibrosis. This can cause pain. The cracks or tears that develop in the annulus fibrosis also can become a source of pain. Finally, the inner nucleus also can come out through the cracks in the annulus and compress nerves or the spinal cord. This condition may cause weakness, pain, a "pins and needles" sensation or numbness. It may require surgery.

Artificial disk replacement video