Disc Herniation and Other Disc Injuries

By: Robert Shepherd MS, Certified Medical Illustrator, President & CEO, MediVisuals Inc.

The term “degenerated disc” is generally used to describe a disc in the early degenerative process. It is the beginning of a progressive break down of the disc. This condition can be initiated or accelerated by a traumatic event.

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A disc bulge is a more advanced collapse of the disc to the point that the disc expands beyond its normal contour. It may or may not impinge on the neural structures within the spinal canal or neural foramina. Similarly, a disc bulge can be the immediate or delayed result of a traumatic event, or a traumatic event may exacerbate a preexisting, stable disc bulge.

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A subligamentous herniation is one in which nucleus pulposus has extended through the annulus fibrosus, but has not gone through the posterior longitudinal ligament.

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The term “herniation” is generally used when the nucleus has completely extruded through the annulus fibrosus and posterior longitudinal ligament. 

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However, it does not matter what the disc pathology is labeled, if it impinges upon, or irritates the neural components, it is a significant injury that will likely require some type of invasive procedure to correct. 

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The disc can either be injured by an immediate tear of the annulus fibrosus and extrusion of the nucleus pulposus during a traumatic event, or they can be the result of a much more gradual process. In order to understand the gradual breakdown of the disc, one must first understand a little of the physiology of a disc. The inner disc relies on exchange of fluid, nutrients and oxygen through the end plate of the adjacent vertebral bodies.

During a traumatic event, the endplate may become injured resulting in interference with that exchange.

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As a result of the inability of the disc to obtain the fluid, nutrients, and oxygen it needs, the disc gradually begins to break down - becoming a degenerated disc, followed by a bulging disc, and eventually to a herniated disc. The amount of time involved with the process of the disc breakdown is related to the severity of the initial disc injury.

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Therefore, if a disc injury is not evident until weeks or months after a traumatic event, it does not mean the injury was not a direct result of the traumatic event.

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Protrusions Versus Extrusions (Intervertebral Disc Pathology, Part 3 of 3)

 By: Robert Shepherd MS, Certified Medical Illustrator, President & CEO, MediVisuals Inc.

This blog is the third in a series referencing language and labels used by health professionals to describe intervertebral disc pathology as defined by a 1995 joint undertaking by representatives from the North American Spine Society, the American Society of Spine Radiology and the American Society of Neuroradiology.  As a result of their efforts, a more uniform and widely accepted use of nomenclature to define intervertebral disc pathology was developed and published in "Nomenclature and Classification of Lumbar Disc Pathology".

The first blog in the series dealt with "Bulges" v. "Herniations", "Symmetrical" and "Asymmetrical" disc bulges and "Broad-based" v. "Focal" herniations.  The second blog addressed "Anular Tears and Fissures".  This blog addresses the use of "Protrusion" and "Extrusion" to describe intervertebral disc herniations.

"Protrusion" and "Extrusion" are essentially used to further classify types of disc herniations. The term "Protrusion" refers to a disc herniation in which the portion of disc material that is outside the normal confines of the disc space is equal to or less than its aperture where the disc material extrudes from the parent disc.   Examples of disc "Protrusions" and "Extrusions" are shown in the below images. 

The image to the left shows a disc "Protrusion".  Note how the superior and inferior dimensions of the disc material that protrudes from its normal confines (highlighted by the arrow on the left) is not as great as the area where the protruding disc material actually exits its normal confines and boundaries (represented by the arrow on the right in the image).  By comparison, the two illustrations to the right show two different disc "Extrusions".  Note how the dimensions of the protruding disc material are greater than the point where it exits its normal confines. 

It is important to appreciate that disc "Protrusions" and "Extrusions" are terms that may be used to further describe "Broad-based" or "Focal" herniations.  For example, the disc pathology referred to in the above illustration as a "Protrusion" could also be "Broad-Based," if it extends between 25 and 50% of the distance around the circumference of the vertebral body.  Similarly, the disc pathology shown in the illustrations referred to as "Extrusions" could also be referred to as "Focal" if extending less than 25% of the distance around the circumference of the vertebral body (see blog from 08/24/11 for further clarification between "Broad-based" and "Focal" herniations).

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