The intervertebral discs
The intervertebral discs are small cartilaginous discs that separate vertebrae and provide some cushion-like action in absorbing shock and preventing friction between vertebrae during movement. They are soft enough to allow smooth movement and lubrication and hard enough to prevent slippage. The intervertebral discs -like all cartilage- are affected by the body’s state of hydration. Their degree of elasticity and flexibility is affected by age, and older individuals are at a higher risk of disc injury and herniation. They are only found in mobile parts of the vertebral column and are, therefore, not found in the sacrum or coccyx.
The intervertebral discs are not soft enough to herniate, but their center is. Structurally, they are formed of a soft part called nucleus pulposus and a firmer part called the annulus fibrosis. The latter firm part surrounds the softer one completely, preventing its herniation, but when increased pressure is exerted, the firm part is torn and the softer part bulges. The herniated disc then compresses either the nerves that come out of the spinal cord in most cases or, much less commonly, the spinal cord itself, causing severe disability. The lumbar group of vertebrae (those found in our lower back) is the most prone to such injury.