Classification of the Pathoanatomy and Symptomatology of Lumbar Intervertebral Disc Disease Part 1: Disc Herniation
Lisi, Anthony J
Lumbar intervertebral disc herniation is a common condition, yet its diagnosis and management are controversial.1-3 Particular controversy exists regarding the safety and effectiveness of chiropractic manipulative technique in the management of this condition. Some report that chiropractic manipulation can be appropriate for lumbar disc herniation,4,5 while others state that such treatment is inappropriate,6-8 and mismanagement of disc problems is the most common malpractice claim to be made against doctors of chiropractic.9
It is, therefore, clearly essential that practicing DCs possess a comprehensive knowledge of the pathology of lumbar disc herniation. This article aims to supply one primary piece of information toward that end: the current nomenclature and classification of the pathology. This may seem a trivial matter to some. Reconciling the many presentations of lumbar disc herniation, the numerous terms that have been used in its description, and the inconsistencies in the meaning of these terms, however, has created great difficulty for spine clinicians. Efforts have been made to overcome this difficulty by standardizing terminology,10 and the prudent doctor of chiropractic will be well served by this knowledge.
The preferred general term for describing the pathology in question is herniated disc. Clinicians may be accustomed to using the term herniated nucleus pulposus; however, this is now considered inaccurate since tissues other than the nucleus (such as cartilage, fragmented annulus, and/or apophyseal bone) are known to be components of displaced disc material.
A herniated disc can be classified with regard to pathoanatomy and/or symptomatology. The most comprehensive attempt to standardize pathoanatomic classification of lumbar disc pathology is the Recommendations of the Combined Task Forces of the North American Spine Society, American Society of Spine Radiology, and American Society of Neuroradiology.10 The task force’s recommendations for description of disc herniation are shown in Table I. A discussion of all seven descriptors is beyond the scope of this article; however, the following text relates features of morphology, containment, and continuity.
Morphology is perhaps the most complicated characteristic to describe. Any displacement of disc material (nucleus, annulus, cartilage, and/or apophyseal bone) beyond the limits of the intervertebral disc space is considered abnormal. A displacement occupying 50 to 100 percent of the disc circumference is called a generalized displacement or bulge, which is not considered a form of herniation. If the distorted material takes up less than 50 percent of the disc circumference, it is termed a localized displacement, which by definition is a herniation. Localized displacements or herniations are further classified as focal if they take up less than 25 percent of the disc circumference, or broad-based if they take up 25 to 50 percent. (Fig. 1A)
A herniated disc is further classified as a protrusion or extrusion, according to its overall shape in relation to its base, the cross-sectional area of disc material at the outer margin of the disc space of origin. A protrusion exists when the base of the herniation (shown in Fig. 1B as the interface between the red and blue portions) is larger in all planes than the part of the herniation that extends beyond the disc space (shown in Fig. 1B as the red portion). By contrast, when the portion of the herniation extending beyond the disc space is larger in any plane than its base, the proper term is extrusion (shown in Fig. 1B in pink). An extrusion in which some of the displaced material has become detached from its disc of origin is said to have lost continuity and is called a sequestration.
The relationship between lumbar disc herniation and low-back pain is controversial.1-3 Several studies have shown that 20 to 76 percent of asymptomatic adults exhibit structural abnormalities of the lumber discs on MRI.11-15 Recently, the term symptomatic lumbar disc disease has been used to differentiate between incidental structural abnormalities and those that are thought to be responsible for a patient’s pain.16-18
When lumbar disc herniation is symptomatic, its presentation can be considered in two broad categories: radicular or discogenic. The former involves the classic situation where herniated disc material contacts and displaces a spinal nerve root. (Fig. 2A) This would lead to the characteristic nerve tension signs and associated neurological findings.
There is evidence, however, that in the absence of nerve root compression, disruption of the lumbar intervertebral disc itself (with or without distortion of the posterior annular margin) can cause low-back pain and/or referred lower-extremity pain, often extending below the knee.19-23 This represents discogenic pain, (Fig. 2B) and the clinical distinction between it and radicular pain is often nebulous. Further clouding the issue is the phenomenon of chemical mdiculitis, which is essentially radiculopathy without displacement of the nerve root. (Fig. 2C) When the outermost layers of the annulus are intact, containment is said to exist. In some cases, however, there is a breach in the outermost layers of the annulus, allowing communication between the nucleus and the vertebral canal. This breach constitutes non-contained pathology, and can result in the so-called leaking disc, where radiculitis occurs via inflammatory and/or immunologic processes.
Further discussion of the pathogenesis, diagnosis, and management of lumbar disc herniation is beyond the scope of this article. For more information, the reader is referred to the above-mentioned Recommendations of the Combined Task Forces of the North American Spine Society, American Society of Spine Radiology, and American Society of Neuroradiology, available online at http://www.asnr.org/spine_nomenclature/Discterms-dec_14.asp.
Nomenclature, although perhaps unglamorous, is essential. It is imperative that practicing chiropractors have a grasp of proper terminology while continuing their study of lumbar disc herniation and when discussing such cases with patients, other providers, and third-party payers. Other phases of lumbar intervertebral disc pathology – annular tears, internal disc disruption, and degenerative disc disease – will be discussed in a future article.
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By Anthony J. Lisi, DC
Dr. Lisi is assistant professor, University of Bridgeport College of Chiropractic. He can be reached at firstname.lastname@example.org.
Dr. Robert Cooperstein is professor, director of technique, Palmer West College of Chiropractic, San Jose, CA. Dr. Cooperstein coordinates this column and accepts manuscript submissions at Cooperstemjemail@example.com, or by fox at 408/944-6118.
Copyright American Chiropractic Association Mar 2004
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