Disc Herniation Types - Bulging, Protruded, Extruded and Sequestered

How a Disc Nucleus Migrates

Herniated disc diagram.
Herniated disc diagram. BSIP/UIG/Universal Images Group/Getty Images

A healthy interaction between your discs and the nearby spinal nerve root is key for keeping back pain away. But when a part (or parts) of a damaged disc herniates, it may press on a nerve. Symptoms of a herniated disc, called radiculopathy, are generally nerve related, and include pain, tingling, numbness, weakness and/or electrical feelings that go down one leg.

We all know that pain is pain. Just the same, 4 types of disc herniation exist and cause symptoms. 

Disc anatomy is such that a soft, jelly-like substance located in the center (called the nucleus pulposus) is contained by tough fibers located on the outside. This outer covering is called the annulus fibrosus. Over time, the annulus can wear down and/or tear, leaving the nucleus and the spinal nerve root vulnerable to an injury. When this occurs, an unhealthy interaction between the herniated disc material and the spinal nerve root may take place, which can lead to pain and/or nerve symptoms.

With each type of disc disruption listed below, the central nucleus is in a different stage of migration towards the outside of annulus, with herniation representing the most extreme version.

Disc Protrusion

A disc protrusion occurs when the disc nucleus bulges but does not rupture. The nucleus remains contained within the disc structure.

Disc Prolapse

When a disc prolapse occurs, the nucleus is still contained within the annulus but only because the outermost fibers are holding it in. (The annulus is made up of several layers of fibers oriented on the diagonal. Each layer lies at an approximately 90-degree angle to the layer above - or below; this design provides scaffolding and support to the whole structure.)

Disc Extrusion

With disc extrusion, the soft material comprising the nucleus escapes from the disc structure to the nearby epidural space but is still connected to the disc. This is possible due to tears in the annular fibers that leave an opening from which the soft material can flow.

Sequestered Disc

In the case of a sequestered disc, fragments from both the annulus and the nucleus make it outside the disc proper. The most common problem resulting from a sequestered disc is an irritated spinal nerve root, occurring because the fragments come into the sensitive nerve material that makes up the spinal nerve root. Generally, the term "herniated disc" is used to refer to a sequestered disc.

Other problems that arise from sequestered discs include myelopathy (pressure or irritation of the spinal cord) and/or cauda equina syndrome (a rare condition in which the exposed nerves at the very end of the spinal cord become pressured. Symptoms of cauda equina — leg pain or weakness that gets progressively worse, "saddle amnesia" and/or problems with bowel or bladder — are generally regarded as a medical emergency.)

When it comes to symptom intensity associated with sequestered discs, it's usually the degree of pressure placed on nerve structures by the freed fragments that is the determining factor.

By the way, it is not always the disc injury alone that creates the pressure on nerve structures; it can be a combination of the injury with the resultant inflammation, as well.

Body Positioning and Your Disc Health

Your body position may determine how much pressure is put on your discs. This is called intradiscal pressure. Generally speaking, the L5-S1 (last lumbar vertebra and top of the sacrum bone interconnection) gets the most pressure. This is because most of the weight of your body is transferred there, plus this spinal segment is a changeover place; in other words, it's where the lumbar spine transitions into the sacral area.

A Swedish study done by Nachemson and Elfstrom measured intradiscal pressure in in the lumbar spine (low back) from various positions. The study started with the premise that when a disc is healthy, pressure tends to be distributed evenly across the entire surface. The researchers took it upon themselves to measure and compare pressure differences between standing (which then served as the comparison value) and a variety of movements, maneuvers, and positions.

They found that walking resulted in less stress than side bending and/or twisting, and side bending and twisting resulted in less stress than jumping, coughing and laughing.

You might think that sitting got the worst marks in this study, but actually the biggest culprit was bending forward, which resulted in very high degrees of intradiscal pressure. The researchers commented that this finding supports what they called "ergonomic advice," i.e. the oft-repeated "bend with your knees and not with your back when you lift something heavy or bulky."

A 2008 study confirmed this, finding that for healthy discs, sitting does no significant damage. In fact, the authors of that study say, sitting and standing are comparable in terms of how much intradiscal pressure they impose.

The only type of maneuver that the researchers found resulting in less pressure than standing was lying down. Apparently, assuming the supine position (lying on your back) likely imposes 50% less intradiscal pressure than the researcher's reference value of standing.

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Article Sources

  • Claus, A., et. al. Sitting versus standing: does the intradiscal pressure cause disc degeneration or low back Pain? J Electromyogr Kinesiol. Aug. 2008. https://www.ncbi.nlm.nih.gov/pubmed/17346987
  • Fishman, L. and Ardman, C., Back Pain: How to Relieve Back Pain and Sciatica. W. W. Norton and Company, New York, London. 1997
  • Magee, David, J. Orthopedic Physical Assessment. 4th Edition. Saunders Elsevier. St. Louis, MO. 2006.
  • Nachemson, A. and Elfstrom, G. Intravital Dynamic Pressure Measurements in Discs. Almqvist & Wiksell. 1970. Stockholm. http://www.energycenter.com/grav_f/studies_nachemson.pdf