Degeneration of the intervertebral discs can result from a variety of conditions, including aging, trauma, and several types of arthritic conditions. As we age, our tissues tend to lose water. That's why skin wrinkles with age, and various body parts begin to sag. When this occurs in the intervertebral disc, the disc tends to shrink, becoming thinner and less cushiony. The condition is fairly common in adults past middle age, and may be asymptomatic - causing no symptoms - other than occasional lower back pain, or stiffness. At other times, however, the associated collapse of the disc space, especially in the lumbar spine (lower back), can be the source of severe mechanical back pain, or radicular leg pain. Under these circumstances, surgical intervention may be appropriate.
The inner portion of the disc, the nucleus pulposis, is composed of proteoglycans - chemical combinations of sugar and protein. When the disc degenerates, small cracks or tears form in the outer annulus, allowing these chemical substances to leak out into the epidural space. Proteoglycans have been shown to cause irritation or inflammation of the nerves surrounding and adjacent to the damaged disc. Minimally invasive, endoscopic procedures, designed to remove the diseased or damaged portion of the disc, may be helpful in alleviating such pain.
Under other circumstances, collapse of the disc space can lead to a condition more recently termed "vertical instability". In this case, shrinkage of the disc allows abnormal movement across a motion segment (2 vertebrae and the intervening disc), and may result in mechanical back pain - pain which arises from changes in position, or attempts at strenuous activities. In such cases, fusion of the interspace may be the procedure of choice. (Perhaps, at some point in the future, replacement of the disc by an artificial substitute may become an option, when such devices are eventually developed and approved for use, by the FDA).