The intervertebral disc is the cartilage pad that sits between the vertebrae, the bones of the spine.
The normal disc is made of two parts:
- the 80% water-filled, jelly-like nucleus pulposus and
- the rubberband-like, sensitive outer fibers (anular fibers) call the anulus fibrosus.
These two parts work together like "shock absorbers" for the spine by holding the vertebrae apart. They also ensure space between the facet joints so they don't irritate each other under normal motions. The disc is the most pain sensitive structure in the spine.
The normal disc may degenerate or herniate. The herniated discs are given all sorts of names -- slipped disc, protruded disc, extruded disc, bulging disc -- but they essentially come down to two types:
- contained discs - Those discs that the center of the disc (nucleus) stays within the outer anular fibers, usually causing low back pain and possibly leg pain.
- non-contained discs - Those discs that the center of the disc (nucleus) escapes through the outer anular fibers, usually resulting in leg pain.