Our intervertebral discs are fascinating structures which provide support to our vertebrae, absorb shock and facilitate all the incredible spinal movements that we make. But can they actually slip out of place? And are “slipped discs” a leading cause of lower back pain? Read on to find out more.
The intervertebral disc is a cartilaginous and articulating structure between the vertebral bodies. Intervertebral discs have the dual role of providing the primary support for the vertebral column while possessing enough elasticity to permit the required mobility of the spine. The discs accounts for 25% to 30% of the overall height of the spine.
Fun fact! We are tallest first thing in the morning when the discs are their most plump, and we slowly become shorter during the day as the discs subtly flatten under our body weight (Botsford et al 1994).
These discs are made up of a central, gelatinous nucleus pulposus that is surrounded by a tough but elastic annulus fibrosis. Collagen fibers continue from the annulus into the adjacent tissues, which ties this structure to each vertebral body at its rim, to the anterior and posterior longitudinal ligaments, and to the cartilaginous endplates superiorly and inferiorly. The nucleus pulposus is a self-contained, pliable gelatinous structure that is approximately 88% water in a healthy young disc. It is essentially a hydraulic system that provides support and separates the vertebrae, absorbs shock, permits transient compression, and allows for movement (Roberts et al 2006).
Vertebrae and intervertebral discs
Our robust intervertebral discs are interwoven with the vertebra and are also supported by many of the spinal ligaments that we have described. The discs themselves cannot ‘slip’ out of place. A ‘ruptured’ disc is also not an accepted medical term and suggests trauma when none has occurred. The technical term is ‘displacement of disc material’.
An intervertebral disc herniation occurs when part of a disc pushes outward beyond its normal boundaries. Medical professionals use several terms to describe the extent or phase of a disc herniation seen on an MRI examination: disc protrusion, disc extrusion and disc sequestration. This classification depends on the condition of the annulus fibrosus and the nucleus pulposus.
A paper by Fardon et al (2014) provides a resource that promotes a clear understanding of lumbar disc terminology among clinicians, radiologists, and researchers: in a disc protrusion the disc and associated ligaments remain intact but form an outpouching that can press against nerves; a disc extrusion occurs when the nucleus squeezes through a weakness or tear in the annulus, but the soft material is still connected to the disc; in a disc sequestration the nucleus not only squeezes out but separates from the main part of the disc. This is also known as a ‘free fragment’. Both a disc extrusion and sequestration can trigger an immune response and inflammation.
While the terms ‘bulging’ and ‘herniated’ are often used interchangeably, there are clinical distinctions between the two: a herniation measures less than 25% of the total disc circumference while a bulge measures greater than 25% of the total disc circumference.
The vast majority of bulges or herniations occur in the posterior direction and slightly laterally (Daghighi et al 2014).
Phases of disc herniation
Deyo (2002) and Jarvik et al (2005) stated that disc bulges and herniations are highly prevalent in pain-free populations, are not strongly predictive of future lower back pain (LBP) and correlate poorly with levels of pain and disability. One literature review showed that in a group of 20-year-olds who were not experiencing back pain, 30% had bulging intervertebral discs (Brinjikji et al 2015). A second review reported that in a group of 50-year-olds who were not experiencing back pain, 60% had bulging discs (Beattie 2008).
It is suggested that herniated disks account for only 4% of LBP cases (Kinkade 2007). There is debate in the literature regarding nociceptive nerve supply to the intervertebral disc and what role the disc plays as a generator of back pain. Studies by Korkala et al (1985) and Palmgren et al (1999) lends support to the concept that the normal intervertebral disc is almost without nerve innervation.
A systematic review of the literature by Chui et al (2015) found that 50% of patients had spontaneous resolution of herniated discs after conservative treatment. They also report that patients with disc extrusion and sequestration had a significantly higher possibility of having spontaneous regression than did those with bulging or protruding discs. Disc sequestration had a significantly higher rate of complete regression than did disc extrusion. Therefore, the more severe the herniation the greater the chance of spontaneous resolution
This short video is taken from my 30-Hour Yoga Anatomy Online Course and demonstrates what can happen during a disc herniation.
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References:
Beattie, P. (2008) ‘Current Understanding of Lumbar Intervertebral Disc Degeneration: A Review with Emphasis Upon Etiology, Pathophysiology, and Lumbar Magnetic Resonance Imaging Findings.’ Journal of Orthopaedic & Sports Physical Therapy 38, 6, 329–340.
Botsford, D., Esses, S. and Ogilvie-Harris, D. (1994) ‘In Vivo Diurnal Variation in Intervertebral Disc Volume and Morphology.’ Spine 19, 8, 935–940.
Brinjikji, W., Luetmer, P., Comstock, B., Bresnahan, B. et al. (2015) ‘Systematic Literature Review of Imaging Features of Spinal Degeneration in Asymptomatic Populations.’ American Journal of Neuroradiology 36, 4, 811-816.
Chiu, C., Chuang, T., Chang, K., Wu, C., Lin, P. and Hsu, W. (2015) ‘The Probability of spontaneous regression of lumbar herniated disc: a systematic review.’ Clin Rehabil 29, 2, 184-195.
Daghighi, M., Pouriesa, M., Maleki, M., Fouladi, D. et al. (2014) ‘Migration patterns of herniated disc fragments: a study on 1,020 patients with extruded lumbar disc herniation.’ Spine Journal 14, 1970–1977.
Deyo, R. (2002). “Diagnostic Evalution of LBP. Reaching a Specific Diagnosis Is Often Impossible.” Archives of Internal Medicine 162, 1444-1447.
Fardon, D., Williams, A., Dohring, E., Murtagh, F., Gabriel Rothman, S. and Sze, G. (2014) ‘Lumbar disc nomenclature: version 2.0: Recommendations of the combined task forces of the North American Spine Society, the American Society of Spine Radiology and the American Society of Neuroradiology.’ Spine J 14, 11, 2525-45.
Jarvik, J., Hollingworth, W., Heagerty, P., Haynor, D., Boyko, E. and Deyo, R. (2005) ‘Three-year incidence of low back pain in an initially asymptomatic cohort: clinical and imaging risk factors.’ Spine 30, 1541-1548.
Kinkade, S. (2007) ‘Evaluation and Treatment of Acute Low Back Pain.’ Am Fam Physician 75, 8, 1181-1188.
Korkala, O., Gronblad, M., Liese, P. and Karaharju, E. (1985) ‘Immunohistochemical demonstration of nociceptors in the ligamentous structures of the lumbar spine.’ Spine 10, 156–7.
Palmgren, T., Grönblad, M., Virri, J., Kääpä, E. and Karaharju, E. (1999) ‘An immunohistochemical study of nerve structures in the annulus fibrosus of human normal lumbar intervertebral discs.’ Spine 24, 2075–9.
Roberts, S., Evans, H., Trivedi, J. and Menage, J. (2006) ‘History and pathology of the human intervertebral disc.’ J Bone Joint Surg Am 88, suppl 2, 10–4.