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 is often called "degenerative disk," and it may cause pain.

Herniated disks

Degenerative changes or strong, jerky movements can cause tears in the intervertebral disk. The escape of the soft interior nucleus of the intervertebral disk through these tears causes the disk to protrude or bulge. When the nucleus breaks through completely, it is called a prolapse or herniated disk. Sequestration of the intervertebral disk occurs when the soft nucleus not only prolapses but also separates completely from the intervertebral disk. As a result, the intervertebral disk and the sheared tissue are no longer firmly connected. The bulging intervertebral disk or the prolapsed soft nucleus now can impinge the nerve paths. Depending on the location of the prolapse, this can cause pain or paralysis symptoms in the back of the neck, arms and shoulders. In extreme cases, the prolapse causes paraplegia.

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