[Neuroanatomic basis for discogenic pain]

The aim of this study is to give a short overview about the innervation of the intervertebral disc and the nerve connections between the somatosensible and autonomous nervous systems in the paravertebral region.

A short review of the clinical and experimental literature including gross-anatomical, histochemical and immunohistochemical studies as well as functional studies after application of tracer substances has been made. We also present our own experimental immunohistochemical and molecular biological investigations on paravertebral muscle biopsies of a patient with post-discotomy syndrome.

The annulus fibrosus of the intervertebral disc is innervated by myelinated nerve fibres. Neuronal markers for pain-leading fibres were found to be positive in the dorsal region of the annulus, and especially in the posterior longitudinal ligament. Nerve ingrowth into the diseased intervertebral disc was found in chronic back pain. The main innervation of the intervertebral disc is formed by the sinuvertebral nerves. The sinuvertebral nerves are recurrent branches of the ventral rami that re-enter the intervertebral foramina to be distributed within the vertebral canal. They are mixed polysegmental nerves and nerve plexuses, each being formed by a somatic root from a ventral ramus and an autonomic root from a grey ramus communicans. The number of nerve bundles was reduced by resection of sympathetic trunks. The expression of neuronal markers in the sarcolemma of the paravertebral muscles is reduced after discotomy.

The neuroanatomical basis of discogenic pain can be summarised as follows: 1. The intervertebral disc receives an extensive innervation, especially the annulus fibrosus. 2. Nerve extension was found into the nucleus pulposus of the degenerated disc. 3. The sinuvertebral nerve plexuses facilitate a polysegmental signal and pain spreading. 4. The innervation of the intervertebral disc is very high connected with the paravertebral muscles. 5. A local denervation of the paravertebral muscles was found in post-discotomy syndrome.