What is Intervertebral Disc Degeneration, and What Causes It?

Michael A. Adams, PhD; Peter J. Roughley, PhD

Disclosures

Spine. 2006;31(18):2151-2161. 

In This Article

Discogenic Pain

The posterior anulus and its adhering longitudinal ligament are supplied by the sinuvertebral nerve, a mixed autonomic and somatic nerve believed capable of nociception, whereas the anterior and lateral regions are supplied by autonomic nerves.[66] Nociceptive nerve fibers normally penetrate only the outermost 1-3 mm of anulus[67,68] but have been reported to progress in toward the nucleus in the anterior regions of painful and severely disrupted discs.[67] The bony vertebral endplate has a similar density of innervation.[69]

Pain provocation studies associate severe back pain with relatively innocuous mechanical stimulation of the outer posterior anulus and endplate.[70] Painful discs are always structurally disrupted[67] and show irregular stress concentrations.[71] They appear to become sensitized to mechanical loading, and animal experiments have confirmed that contact with nucleus pulposus can lower nerve stimulation thresholds in adjacent tissues.[72] Pain sensitization is of most functional significance when it occurs in the outer anulus fibrosus because that is where the highest stress concentrations are found in degenerated discs (Figure 3C).

Features of discs most closely associated with pain include disc prolapse,[49] disc narrowing,[73,74] radial fissures,[73,75] especially when they reach the disc exterior and leak,[76] and internal disc disruption, including inward collapse of the anulus.[77] More variably related to pain are endplate fracture and Schmorl nodes,[78] and disc bulging.[49,73,78,79] Disc signal intensity on magnetic resonance imaging (MRI) has little if any relationship to pain.[73]

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