Posterior Disc Bulge vs Herniated Disc

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Area of a bulging disc
Area of a bulging disc. decade3rd

With so many descriptive terms and glossary items for disc related problems, it's easy to get overwhelmed when researching your diagnosis. In this article, we'll distinguish between two common intervertebral disc conditions: the bulging disc and the herniated disc.

What is a Bulging Disc

A bulging disc occurs when the nucleus pulposus — the soft, jelly-like center of the disc that gives the disc shock-absorbing capacities — extends beyond its normal position inside the disc structure, but remains contained within the annulus fibrosus. The annulus fibrosus is the tough outer covering of the disc, that, when healthy and without tears, keeps the nucleus pulposus contained. The annulus is made of fibrous material organized concentrically in a criss-cross patterning.

In an undamaged intervertebral disc, the outer edge, i.e., the annulus fibrosus, tends to line up with the edge of the vertebra to which it is attached. But as the name suggests, bulging discs do extend past this boundary.

How far?

Generally, not more than 3 millimeters.

Authors of a 2011 study published in the December issue of Global Spine Journal, say that a number of things — from the height of your disc to the degree of mobility between the spinal bones above and below — factor into the migration of a bulging disc. 

Migration is a movement of the disc inside the annulus fibrosus. The study looked at how bulges got bigger or smaller depending on the position of the spine.

Regardless of the variables, one thing the authors are sure of is that the amount of disc migration is associated with the degree of degenerative changes present in the spine. 

In general, such changes may or may not cause discogenic pain.

What Causes a Bulging Disc?

Bulging discs may be caused by a number of things. Perhaps the most common is age related degenerative changes that occur in the spine. The term degenerative changes refers to the effects of wear and tear on the disc that accumulate over time.

Dehydrating discs, which are also related to degenerative changes, poor posture, a job that involves routine heavy lifting or exposure to ergonomic risk factors, a history of one or more spine injuries and genetics are other things that may lead to a bulging disc.

Believe it or not, a small bulge in your disc that shows up on an MRI may actually be a normal finding. In other words, a bulging disc may simply be a slight variation in standardly described anatomy.

And while bulging discs may cause pain, they don't always do so. That said, a bulging disc may be a sign that you're in the first stage of disc disease. 

When a bulging disc does cause pain, it may be because the disc is pressing on the spinal cord or a spinal nerve root. Resultant symptoms may include pain, weakness, numbness and/or electrical sensations that go down one leg or one arm.

Herniated Disc

Unlike a disc that is bulging, a herniated disc occurs when tears in or ruptures of the outside of the annulus allow ​some of the soft material nucleus pulposus to exit the disc. Pain and other symptoms related to herniated disc may occur should the escaped nucleus pulposus comes into contact with a spinal nerve root. 

Herniated discs are usually caused either by degenerative changes in the spine and disc or by an injury.

Similar to bulging discs, herniated discs are not always symptomatic. Whether they are or not generally depends on if the leaked disc material makes contact with nerve tissue. When symptoms do occur, they may be similar to those of a herniated disc, i.e., pain, nerve related sensations, weakness and/or numbness that go down one arm or leg.

But contrary to popular belief, a bulging disc is not a lighter version of a herniated disc, according to a 2014 report published in the Spine Journal.

That said, herniated discs progress in stages, from prolapsed to protruding, extruding and finally to sequestration, where the disc material is completely severed from the main disc structure.

A Word from Verywell

One way to remember the difference between a bulging and a herniated disc is related to where the damage starts. If the damage starts internally, i.e., affecting the inside part of annulus's fibers, it will likely leave the soft material of the nucleus intact. This describes a bulging disc.

On the other hand, a herniated disc occurs when the outside of the annulus fibrosus is torn or somehow compromised, allowing the inner nucleus to leak outside the disc structure.

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