Herniated Disk Health Article

Definition

Disk herniation is a rupture of fibrocartilagenous material (annulus fibrosis) that surrounds the intervertebral disk. This rupture involves the release of the disk's center portion containing a gelatinous substance called the nucleus pulposus. Pressure from the vertebrae above and below may cause the nucleus pulposus to be forced outward, placing pressure on a spinal nerve and causing considerable pain and damage to the nerve. This condition most frequently occurs in the lumbar region and is also commonly called herniated nucleus pulposus, prolapsed disk, ruptured intervertebral disk, or slipped disk.

Description

The spinal column is made up of 26 vertebrae that are joined together and permit forward and backward bending, side bending, and rotation of the spine. Five distinct regions comprise the spinal column, including the cervical (neck) region, thoracic (chest) region, lumbar (low back) region, sacral and coccygeal (tailbone) region. The cervical region consists of seven vertebrae, the thoracic region includes 12 vertebrae, and the lumbar region contains five vertebrae. The sacrum is composed of five fused vertebrae, which are connected to four fused vertebrae forming the coccyx. Intervertebral disks lie between each adjacent vertebra.

Each disk is composed of a gelatinous material in the center, called the nucleus pulposus, surrounded by rings of a fibrous tissue (annulus fibrosus). In disk herniation, an intervertebral disk's central portion herniates through the surrounding annulus fibrosus into the spinal canal, putting pressure on a nerve root. (There is often a progression of small fissures in the annulus fibrosis before the disk herniates.) Disk herniation most commonly affects the lumbar region between the fifth lumbar vertebra and the first sacral vertebra. However, disk herniation can also occur in the cervical spine. The incidence of cervical disk herniation is most common between the fifth and sixth cervical vertebrae. The second most common area for cervical disk herniation occurs between the sixth and seventh cervical vertebrae. Disk herniation is less common in the thoracic region.

Predisposing factors associated with disk herniation include age, gender, and work environment. The peak age for occurrence of disk herniation is between 20–45 years of age. Studies have shown that males are more commonly affected than females in lumbar disk herniation by a 3:2 ratio. Genetic factors are suspected of playing a role in disk herniation. Prolonged exposure to a bent-forward work posture is correlated with an increased incidence of disk herniation. Pain from a herniated disk is usually greatest when sitting and is lessened when standing.

There are four classifications of disk pathology:

• A protrusion may occur where a disk bulges without rupturing the annulus fibrosis.
• The disk may prolapse where the nucleus pulposus migrates to the outermost fibers of the annulus fibrosis.
• There may be a disk extrusion, which is the case if the annulus fibrosis perforates and material of the nucleus moves into the epidural space.
• The sequestrated disk may occur as fragments from the annulus fibrosis and nucleus pulposus are outside the disk proper.