The intervertebral disc (discus intervertebralis) lies between two adjacent vertebral bodies of the spine. It consists of an outer fibrous ring (anulus fibrosus) and an inner gel-like core (nucleus pulposus).
Functionally it acts as a shock absorber between the vertebrae while allowing small movements in several axes. With increasing age, the water content of the nucleus pulposus decreases, which can change the height and load capacity of the disc. If the fibrous ring is more severely damaged, bulges (protrusion) or herniations (prolapse) can occur.