The soft, intervertebral disc is the most commonly injured part of the spine. This condition, called a ruptured or herniated disc, typically results in part of the disc bulging out, causing compression on the adjacent nerve root. This can cause back and/or leg pain symptoms.
The intervertebral disc is composed of two layers. The outer portion consists of thicker layers of collagen, and is called the annulus fibrosis. The softer, inner portion of the disc is called the nucleus pulposus. When there is an injury to the annulus fibrosis, the nucleus pulposus material can extrude out. This can cause inflammation and/or compression on the adjacent spinal nerve.
Another common spinal condition is spondylosis (arthritis of the spine), which is the result of wear-and-tear changes to the spinal column. These changes include degeneration of the intervertebral disc, which causes the disc to lose water content and its soft, cushion characteristics. The disc becomes flat and hard, which can lead to pain and stiffness. This may produce narrowing of the foramen and cause nerve impingement. The arthritic process also includes the formation of bone spurs and facet joint hypertrophy (overgrowth), which can cause spinal stenosis (narrowing of the spinal canal and pinching of the spinal nerves).
Spondylolisthesis is defined as one spine bone slipping forward on another one, causing instability and/or pain. Spondylolisthesis can occur because of a fracture or arthritis, or other spinal problems.