Intervertebral Discs

Along with the twenty-four vertebrae, your spinal column is also composed of a series of intervertebral discs that lie between adjacent vertebrae. Each disc and the vertebrae on either side of it form a joint. Just as the meniscus absorbs forces at the knee, the intervertebral discs act as pillows to absorb or distribute forces applied to the spine. They also contribute to the stability of the spine, help maintain proper alignment of the spine, and permit movement. You can think of intervertebral discs as tiny round gel packs. The outside of each disc is composed of a substance called fibrocartilage, which is a combination of cartilage and fibrous connective tissue. This fibrocartilage is known as the annulus fibrosus, and it is tough, flexible, and elastic. Inside of each of the discs (the nucleus pulposus) is a gel that is composed primarily of proteoglycans and water. This gel resists compression and therefore makes a good shock-absorbing center for the discs. This almost avascular (that is, lacking blood vessels) structure bears some of the greatest loads in the human body. There are twenty-three discs in the spine, and they are named according to which vertebrae they separate (for instance, C5-6 is the disc between the fifth and sixth cervical vertebrae).