Academy of Chiropractic’s

Lawyers PI Program


 From the Desk of:


"Disc Definitions: Reference Guide


Succeeding in practice means that you have to be the best-of-the-best at what you do and have formal credentials to back it up. I urge you to take courses that will give you the knowledge and credentials so that when you are challenged with either a diagnostic dilemma or on the witness stand, both you and chiropractic win because you are the "real deal." That is the only way we individually, and as a profession can prevail for generations to come.

Published in The American Chiropractor, December, 2009, 31(12), p. 44-46

Disc Definitions


In order to understand disc pathology, you must first understand accepted definitions. The following are from the Recommendations of the Combined Task Forces of the North American Spine Society, American Society of Spine Radiology, and American Society of Neuroradiologypublished on the Web site of the American Society or Neuroradiology. In working with different disciplines, it is critical to be using the same language to communicate clearly in creating an accurate diagnosis:

Since its publication, the following nomenclature has been endorsed by the following professional organizations and scientific societies:

American Academy of Orthopaedic Surgeons (AAOS)
American Academy of Physical Medicine and Rehabilitation (AAPM&R)
American College of Radiology (ACR)
American Society of Neuroradiology (ASNR)
American Society of Spine Radiology (ASSR)
Joint Section on Disorders of the Spine and Peripheral Nerves of the American Association of Neurological Surgeons (AANS)
Congress of Neurological Surgeons (CNS)
European Society of Neuroradiology (ESNR)
North American Spine Society (NASS)
Physiatric Association of Spine, Sports and Occupational Rehabilitation (PASSOR)
American Academy of Medical Legal Professionals (AAMLP)

Normal: Categorization of a disc as "Normal" means the disc is fully and normally developed and free of any changes of disease, trauma, or aging. Only the morphology, and not the clinical context, is considered.

Annular Tears/Fissures: Loss of integrity of the anulus, such as radial, transverse, and concentric separations. In the case where a single, traumatic event is clearly the source of loss of integrity of a formerly normal anulus, such as with documentation and findings of violent distraction injury, the term "rupture" of the anulus is appropriate, but use of the term "rupture" as synonymous with commonly observed tears or fissures is contraindicated. In conclusion, therefore, "anular tear" and "annular fissure" are both acceptable terms, can be used properly as synonyms, and do not imply that a significant traumatic event has occurred or that the etiology is known.

Ruptured Anulus: Disruption of the fibers of the anulus by sudden violent injury. Note: Separation of fibers of the anulus from degeneration, repeated minor trauma, other non-violent etiology, or when injury is simply a defining event in a degenerative process should be termed fissure or tear of the anulus. Rupture is appropriate when there is other evidence of sudden violent injury to a previously normal anulus. Ruptured anulus is not synonymous with ruptured disc, which is a colloquial equivalent of disc herniation.

Disc Degeneration: 1. Changes in a disc characterized by desiccation, fibrosis and cleft formation in the nucleus, fissuring and mucinous degeneration of the anulus, defects and sclerosis of end-plates, and/or osteophytes at the vertebral apophyses. 2. Imaging manifestations commonly associated with such changes. 3. (Non-Standard) [Changes in a disc related to aging.] Because there is confusion in differentiation of changes of pathologic degenerative processes in the disc from those of normal aging the classification category "Degenerative/Traumatic" includes all such changes, thus does not compel the observer to differentiate the pathologic from the normal consequences of aging. With normal aging, fibrous tissue replaces nuclear mucoid matrix, but the disc height is preserved and the disc margins remain regular. Radial tears of the anulus are found only in a minority of post-mortem examinations of individuals over 40 years old, and therefore cannot be considered a usual consequence of aging

Desiccated Disc: 1. Disc with reduced water content, usually primarily of nuclear tissues. 2. Imaging manifestations of reduced water content of the disc; or apparent reduced water content, as from alterations in the concentration of hydrophilic glycosaminoglycans.

Herniated Disc: 1. Localized displacement of disc material beyond the normal margins of the intervertebral disc space. 2. (Non-Standard) [Any displacement of disc tissue beyond the disc space]. Note: Localized means, by way of convention, less than 50% (180 degrees) of the circumference of the disc. Disc material may include nucleus, cartilage, fragmented apophyseal bone, or fragmented annular tissue. The normal margins of the intervertebral disc space are defined, craniad and caudad, by the vertebral body end-plates and peripherally by the edges of the vertebral body ring apophyses, exclusive of osteophytic formations. Herniated disc generally refers to displacement of disc tissues through a disruption in the anulus, the exception being intravertebral herniations (Schmorl's nodes) in which the displacement is through vertebral end-plate. Herniated discs in the horizontal (axial) plane may be further subcategorized as protruded or extruded. Herniated disc is sometimes referred to as "herniated nucleus pulposus," but the term herniated disc is preferred because displaced disc tissues often include cartilage, bone fragments, or annular tissues.

To be considered "herniated," disc material must be displaced from its normal location and not simply represent an acquired growth beyond the edges of the apophyses, as is the case when connective tissues develop in gaps between osteophytic formations. Displacement, therefore, can only occur in association with disruption of the normal anulus or, as in the case of intravertebral herniation (Schmorl's node), a break in the vertebral body end-plate. Since details of the integrity of the anulus are often unknown, the distinction of herniation is usually made by observation of displacement of disc material beyond the edges of the ring apophyses that is "localized," meaning less than 50% (180 degrees) of the circumference of the disc. Generalized, meaning greater than 50%, displacement of disc material beyond the ring apophyses, or adaptive changes of the apophyses and/or outer anulus to adjacent abnormality, such as may occur with scoliosis or spondylolisthesis, are not herniations. The 50% cut-off line is established by way of convention to lend precision to terminology and does not demarcate etiology, relation to symptoms, or treatment indications.

Broad-Based ProtrusionHerniation of disc material extending beyond the outer edges of the vertebral body apophyses over an area greater than 25% (90 degrees) and less than 50% (180 degrees) of the circumference of the disc. See protrusion. Note: Broad based protrusion refers only to discs in which disc material has displaced in association with localized disruption of the anulus and not to generalized (over 50% or 180 degrees) apparent extension of disc tissues beyond the edges of the apophyses

Bulging Disc: The term "bulge" refers to an apparent generalized extension of disc tissues beyond the edges of the apophyses. Such bulging occurs in greater than 50% of the circumference of the disc and extends a relatively short distance, usually less than 3 mm, beyond the edges of the apophyses. "Bulge" describes a morphologic characteristic of various possible causes. Bulge is a term for an image that requires a differential diagnosis. Bulging is sometimes a normal variant (usually at L5-S1); can result from advanced disc degeneration or from vertebral body remodeling (as consequent to osteoporosis, trauma, or adjacent structural deformity); can occur with ligamentous laxity in response to loading or angular motion; can be an illusion caused by posterior central sub-ligamentous disc protrusion; or can be an illusion from volume averaging (particularly with CT axial images).

Bulging, by definition, is not a herniation. Herniation is present if there is localized displacement of disc material, and not simply outward overlapping, as is the case with some types of bulging.

Protruded Discs: A disc is "protruded," if the greatest distance, in any plane, between the edges of the disc material beyond the disc space is less than the distance between the edges of the base in the same plane. The term "protrusion" is only appropriate in describing herniated disc material, as discussed above.

Protrusions may be "focal" or "broad-based." The distinction between focal and broad-based is arbitrarily set at 25% of the circumference of the disc. Protrusions with a base less than 25% (90 degrees) of the circumference of the disc are "focal." If disc material is herniated so that the protrusion encompasses 25% to 50% of the circumference of the disc, it is considered "broad-based protrusion."

Extruded Discs: extruded disc, extrusion (n), extrude (v): A herniated disc in which, in at least one plane, any one distance between the edges of the disc material beyond the disc space is greater than the distance between the edges of the base in the same plane, or when no continuity exists between the disc material beyond the disc space and that within the disc space. Note: The preferred definition is consistent with the common language image of extrusion as an expulsion of material from a container through and beyond an aperture. Displacement beyond the outer anulus of disc material with any distance between its edges greater than the distance between the edges of the base distinguishes extrusion from protrusion. Distinguishing extrusion from protrusion by imaging is best done by measuring the edges of the displaced material and remaining continuity with the disc of origin, whereas relationship of the displaced disc material to the aperture through which it has passed is more readily observed surgically. Characteristics of protrusion and extrusion may co-exist, in which case the disc should be subcategorized as extruded. Extruded discs in which all continuity with the disc of origin is lost may be further characterized as sequestrated. Disc material displaced away from the site of extrusion may be characterized as migrated. See: herniated disc, migrated disc, protruded disc.

Sequestered Discs: free fragment: Extruded disc material that has no continuity with the disc of origin may be further characterized as "sequestrated". A sequestrated disc is a subtype of "extruded disc" but, by definition, can never be a "protruded disc." Disc material that is displaced away from the site of extrusion, regardless of continuity, may be called "migrated," a term which is useful for the interpretation of imaging studies because it is often impossible from images to know if continuity exists. Note: Sequestrated disc and free fragment are virtually synonymous. When referring to the condition of the disc, categorization as extruded with sub-categorization as sequestrated is preferred, whereas free fragment or sequestrum is appropriate when referring specifically to the fragment.

Protrusion/Extrusion: The use of the distinction between "protrusion" and "extrusion" is optional and some observers may prefer to use, in all cases, the more general term "herniation". Further distinctions can often be made regarding containment, continuity, volume, composition, and location of the displaced disc material.