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The pathogenesis of both acute and chronic low back pain remains poorly understood. Innervation of the intervertebral discs may hold some insight about sources and mechanisms of pain. In healthy, nonsufferers of low back pain, nerve fibers extend only about one-third the depth of the annulus fibrosis. On the other hand, some studies have reported finding nerves throughout the entire depth of the annulus fibrosis, and even penetrating as far as the annulus fibrosis.
To study this phenomenon, 57 biopsy samples of intervertebral discs were obtained at the time of surgery for chronic back pain. In comparison, 82 samples of intervertebral discs were obtained from age- and sex-matched cadavers within eight hours of death in the hospital in patients with no known history of back pain.
Biopsy specimens from low back pain sufferers at the level of their disc involvement showed neovascularization of the annulus fibrosis and nucleus pulposus. Additionally, neural structures not present in control specimens were found through the full depth of the annulus and into the nucleus pulposus.
It is hypothesized that this new nerve growth in low back pain sufferers represents an attempted healing process. Since these nerves mediate pain at least in part through Substance P, treatments that alter this aberrant nerve growth or modulate Substance P may become of value in the treatment of low back pain.
Freemont AJ. Lancet 1997;350: 178-181.