Objective: The first quantitative analysis of the innervation of the lumbar intervertebral disc is presented.
Methods: A sheep model was used allowing evaluation of the whole motion segment. Four sheep spines were used. One was processed for PGP 9.5 immunofluorescence and three were processed for PGP 9.5 immunoperoxidase histochemistry. A count was made of the densities of innervation of the endplate and anulus, and these were compared.
Results: There is no significant difference between endplate and anulus innervation densities. The endplate innervation is concentrated centrally adjoining the nucleus. The richest area of innervation is in the perianular connective tissue.
Discussion: The lumbar intervertebral disc has a meager innervation. This is concentrated in the perianular connective tissue and the central endplate. Although receptor threshold is more closely related to nociceptive function than innervation density, these findings have important implications for any treatment of discogenic pain.