Causes

Causes of Degenerative Disc Disease

A healthy intervertebral disc has a great deal of water in the nucleus pulposus (the center portion of the disc). The water content gives the nucleus a spongy quality and allows it to absorb spinal stress. Excessive pressure or injuries to the disc can cause the injury to the annulus (the outer ring of tough ligament material) that holds the vertebrae together. The annulus is generally the first portion of the disc to be injured. Small tears show up in the ligament material of the annulus. These tears heal by scar tissue, which is not as strong as normal ligament tissue. The annulus becomes weaker over time as more scar tissue forms. This can lead to damage of the nucleus pulposus. It begins to lose its water content and dry up. View animation of degeneration.

Loss of water content causes the discs to lose some of their ability to act as cushions. This can lead to even more stress on the annulus and still more tears as the cycle repeats itself. As the nucleus loses its water content, it collapses, allowing the two vertebrae above and below to move closer to one another. This results in a narrowing of the disc space between the two vertebrae. As this shift occurs, the facet joints (located at the back of the spine) are forced to shift. Shifting changes the way the facet joints work together and can cause problems as well.

Bone spurs, sometimes called osteophytes, may begin to form around the disc space. These can also form around the facet joints. This is thought to be due to the body's response to try to stop the excess motion at the spinal segment. The bone spurs can become a problem if they start to grow into the spinal canal and press into the spinal cord and spinal nerves. This condition is called spinal stenosis.