Posterior Disc Bulge vs. Herniated Disc

Bulging discs and herniated discs sound like similar problems. While they do have some similarities, they also have important differences, including what causes them.

Contrary to popular belief, a bulging disc is not a lighter version of a herniated disc. The main difference between a bulging and herniated disc is where the damage starts.

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 keeps the nucleus pulposus contained when it's healthy and without tears. The annulus is made of fibrous material organized concentrically in a criss-cross pattern.

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

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 the 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.

The amount of disc migration is associated with the degree of degenerative changes present in the spine. Generally, a disc bulge is not more than 3 millimeters (mm).

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

Bulging Disc Causes

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 accumulates over time.

Other things that may lead to a bulging disc include:

• Dehydrating discs (related to degenerative changes)
• Poor posture
• Routine heavy lifting
• Routine exposure to ergonomic risk factors
• One or more previous spine injuries
• Genetics

A bulging disc may be a sign that you're in the first stage of disc disease.

While bulging discs may cause pain, they don't always. When a bulging disc does cause pain, it may be because the disc is pressing on the spinal cord or a spinal nerve root.

Symptoms may include:

• Pain
• Weakness
• Numbness
• Electrical sensations running down a limb

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 a herniated disc may occur if 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 whether the leaked disc material makes contact with nerve tissue.

When symptoms do occur, they may be similar to those of a bulging disc, i.e., pain, nerve-related sensations, weakness, and/or numbness that go down one arm or leg.

A Word From Verywell

A herniated disc and a bulging disc form differently. A bulging disc starts internally—affecting the inside part of annulus's fibers—it will likely leave the soft material of the nucleus intact.

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.

It is hard to know which one of these you have based on symptoms alone. It's important to get a diagnosis and treatment to alleviate discomfort and prevent the condition from worsening.