The intervertebral discs are the largest avascular tissues in the body. They link the vertebral bodies and are the major joints of the spine, providing flexibility to an otherwise rigid structure. These large tissues are maintained by only a small population of cells; the cell density is one of the lowest of any tissue in the body with one cell responsible for synthesizing and maintaining as much as 200 times its volume of matrix. The discs show signs of degenerative change very early in life, possibly because of the hostile environment that they encounter; their nutrient supply is precarious and they experience high mechanical loads. Although recent work indicates that much degeneration is genetically determined, interactions between genes and the physical environment appear to increase the risk of disc degeneration, which itself is associated with one of the most costly medical conditions in the Western world, back pain.

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