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What is the Annulus Fibrosus?


Updated June 12, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

The annulus fibrosus is the tough outer covering of the intervertebral disc.

The annulus fibrosus is the tough covering on the outside of the intervertebral disc.

(c) Anne Asher 2010 Licensed to About.com

The annulus fibrosus is the strong wrapping that makes up the outside portion of the intervertebral disc. Its job is to contain and protect the soft material located in the center of the disc. This soft center is called the nucleus pulposus. The nucleus pulposus (and the entire intervertebral disc) provides shock absorption for the spine.

The annulus, as it is called for short, consists of several concentric rings of fibrous cartilage. The fibers run on a diagonal angle. Fibers of each separate layer run at a right angle to the fibers in the ring next to it. This design increases the strength of the annulus.

Pronunciation: an-u-luhs fi-broh-sus
Also Known As: Annulus
Alternate Spellings: Annulus fibrosis
A tear in the annulus fibrosus, known as an annular tear, may be the source of a herniated disc.
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