A vertebral disc is the shock-absorbing structure between each vertebra. The disc has a thick outer layer (annulus) that surrounds the soft gel-like center (nucleus). Intervertebral discs act as cushions in between vertebrae. The spinal canal, containing the spinal nerves, lies directly behind the disc and the vertebral bodies.
With degenerative disc disease, the intervertebral disc shrinks in height, and bulges out into the surrounding spinal canal. The alignment of the spine may decompensate, and the patient may tilt forward due to the collapsed disc. Nerve roots can also become pinched by the disc protruding and compressing the nerve roots, or due to the loss of disc height.