Raoul S,et al.
Surg Radiol Anat. 2003 Feb;24(6):366-71. Epub 2003 Feb 5.

Abstract
Low back pain is frequent and results in major disability for patients. This anatomical study was done to understand mechanisms involved in that pain. Two kinds of innervation are present in the lumbar spine: one depends on the somatic nervous system and the other on the sympathetic nervous system. The sympathetic nerves are the sinu-vertebral nerves and the rami communicantes which innervate the intervertebral disc, the ventral surface of the dura mater, the longitudinal dorsal ligament and the longitudinal ventral ligament. The sinu-vertebral nerve was described first by Luschka in 1850. This nerve is implicated in diffuse low back pain because of its pathway and its sympathetic component. This nerve cannot directly reach a somatic element at each level of the lumbar spine, so must first reach the L2 spinal ganglion. Thus, there is a “hole” in the somatic innervation between L3 and L5 because the dorsal nerves do not reach the skin at these levels. The pain therefore takes another route through the sympathetic system. Discogenic pain is mediated by the sinu-vertebral nerves, and through the rami communicantes reaches the L2 spinal ganglion. Anatomical and clinical features reinforce this hypothesis.

PubMed Reference:  http://www.ncbi.nlm.nih.gov/m/pubmed/12647025/