It has been thought that lumbar intervertebral discs were innervated segmentally. We have previously shown that the L5-L6 intervertebral disc in the rat is innervated bilaterally from the L1 and L2 dorsal root ganglia through the paravertebral sympathetic trunks, but the pathways between the disc and the paravertebral sympathetic trunks were unknown.We have now studied the spines of 17 rats to elucidate the exact pathways. We examined serial sections of the lumbar spine using immunohistochemistry for calcitonin gene-related peptide, a sensory nerve marker. We showed that these nerve fibres from the intervertebral disc ran through the sinuvertebral nerve into the rami communicantes, not into the corresponding segmental spinal nerve.In the rat, sensory information from the lumbar intervertebral discs is conducted through rami communicantes. If this innervation pattern applies to man, simple decompression of the corresponding nerve root will not relieve discogenic pain. Anterior interbody fusion, with the denervation of rami communicantes, may be effective for such low back pain. [Br] 1998;80-B:737-42.
J Bone Joint Surg
Received 4 August 1997; Accepted after revision 8 January 1998Lumbar intervertebral discs and facet joints are possible sources of low back pain, 1-3 but they have been considered to have a segmental sensory innervation. Recent studies in rats, however, have shown that the L5-L6 disc and part of the L5-L6 joint capsules are innervated by sensory neurones of the L1 and L2 dorsal root ganglia through the paravertebral sympathetic trunk, 4-10 although the fibre pathways between the disc and the sympathetic trunk are not known. Many reports have described fibres connecting the sinuvertebral nerve from the disc to rami communicantes tethered to the paravertebral sympathetic trunk, but they were thought to be sympathetic postganglionic nerve fibres. [11][12][13][14][15] Connections through the sinuvertebral nerve between the intervertebral disc and the rami communicantes have not yet been identified. We have investigated the distribution and course of both sensory and sympathetic postganglionic nerve fibres to the lumbar intervertebral disc in rats, using immunohistochemical methods. We paid special attention to the connections with rami communicantes and the segmentally corresponding spinal nerve.
Materials and MethodsWe anaesthetised 17 Sprague-Dawley rats at 0 to 7 days after birth by cooling to 4°C. They were then transcardially perfused with 0.9% saline, followed by 100 ml of 4% paraformaldehyde in 0.1 M phosphate buffer (pH 7.4). The spinal column with its muscles from T13 to S1 was removed, immersed in the same fixative overnight at 4°C, and then decalcified for four days in 10% ethylenediaminetetra-acetic acid (Wako Chemical, Tokyo, Japan). After storage in 0.01 M phosphate-buffered saline (PBS) containing 20% sucrose for 24 hours at 4°C, the samples were serially sectioned at 40 m in a sagittal plane on a cryostat, and the sections placed on slide glasses.Endogenous tissue peroxidase activity was...