What is the Annulus Fibrosus?

Intervertebral Disc
Intervertebral Disc. BSIP/UIG/Collection:Universal Images Group/Getty Images

What is the Annulus Fibrosus?

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 scaffolding design increases the strength of the annulus fibrosus as a whole, allowing it to fulfill its purpose as a container for the nucleus pulposus.

Annular Tears

One common injury to the annulus is a tear.  Tears can be painful or asymptomatic.  Quite often a tear can be successfully treated by conservative means only, in other word, with physical therapy.  Sometimes tears lead to bulging or herniated discs, but not always.

Related:  Annular Tear

Most of the time, medical treatments for the intervertebral disc are focused on containing (or clearing away pieces of) the nucleus pulposus. 

But more recently, scientists and clinicians have been working on ways to strengthen and/or repair the annulus.  According to Bron, et. al. in their article, "Repair, regenerative and supportive therapies of the annulus fibrosus: achievements and challenges," which was published in the March 2009 issue of the European Spine Journal, this new direction may be required to prevent re-herniation.

  The authors that say strengthening and repairing the annulus may actually increase the potential of nucleus pulposus repair, because without it, the normal amount of disc pressure (which is necessary for the disc’s main task of shock absorption) cannot be restored.

This new direction is in its infancy, which means while there’s been testing on animals, treatments that work on people are still a ways out.

  Meanwhile, here is Bron, et. al.’s list of potential approaches to annulus fibrous strengthening and repair:

The Surgical Approach to Annulus Repair

Suturing, according to Bron, et. al. is designed to contain the nucleus pulposus in a disc replacement surgery.  But it doesn't restore lost fibers, nor does it reverse any damage.  The researchers say a number of products are already in use during surgery that address some of these issues, but they task future researchers to come up with and perfect even more effective methods.

Annulus Fibrosus Regeneration

Regenerating the fibers of the annulus, by means of tissue engineering, is in some ways, according to Bron, et. al., a better solution than suturing. The problem is, it’s much more difficult for scientists to pull off.   The 3 types of techniques that are in the works are:  Generating annulus cells, using gene and bio-active factors to influence extra cellular matrix productions, and scaffolding.

The researchers say ideally an annulus regeneration strategy will combine techniques that close the tear and regenerate the tissue at the same time, and that gene and bio-active strategies cannot be used as standalone treatments, but rather in combination with scaffolding.

Related: Should you get a Chiropractic Adjustment for Post Back Surgery Pain?


Bron, J. L., et. al. Repair, regenerative and supportive therapies of the annulus fibrosus: achievements and challenges. Eur Spine J. 2009 Mar; 18

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