Disc degeneration can be difficult to understand, so to make it easier, compare a spinal segment to two vanilla wafers (the "vertebrae") and a marshmallow (the "disc"). Imagine two wafers with a fresh marshmallow between them. When you press the wafers close together, the marshmallow gives or "squishes out". Suppose you leave the marshmallow out for a week and it starts to dry out. When you press it between the wafers, it is not quite as spongy. If you press hard enough, the outside of the marshmallow may even tear or split. Suppose you left the marshmallow out for a month. It would probably be so dried out it would be hard and very thin and would not have any "shock absorbing" ability.

The older that we get, the more our disc loses water content, and  as a result, some of its shock absorbing ability. Like the marshmallow, the first changes that occur in the disc are tears in the outer ring of the disc, called the annulus. Because tears in the annulus may occur without symptoms, you may not notice when they occur or what caused them. These tears heal by forming scar tissue. Scar tissue is weaker than normal tissue. Repeated injuries and tears cause more wear and tear to the disc. As the disc wears, it loses more of its water content. It becomes less and less "spongy", eventually no longer able to act as a shock absorber.

As the disc continues to wear, it begins to collapse. The space between each vertebra becomes smaller. The collapse also affects the way that the facet joints in the back of the spine "line up". Like any other joint in the body, the change in the way the bones fit together causes abnormal pressure on the articular cartilage. Articular cartilage is the smooth shiny material that covers the end of the bones in any joint. Over time, this abnormal pressure causes wear and tear arthritis (osteoarthritis) of the facet joints.

Bone spurs may form around the disc and facet joints. It is thought that too much motion in a spinal segment causes the bone spurs to form. Eventually, bone spurs can form around the nerves of the spine, causing a condition called spinal stenosis.

To read more about the causes of back pain, click here.