Abstract
Introduction: Although it is well recognized that the outer annulus is innervated, the relative densities of innervation of different regions of the disc have not been quantitated. We present here the first comparative analysis of the innervation of the innervation of different regions of the lumbar intervertebral disc.
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 immunoflourescence and three were processed for PGP 9.5 immunoperoxidase histochemistry. Serial sagittal sections were obtained and a count was made of the densities of innervation of different regions of the endplate and annulus. These were compared to identify which areas of the disc and endplate are most innervated.
Results: The endplate innervation is concentrated centrally adjoining the nucleus. The mean density of innervation of the central endplate was 0.44 (SEM 0.07) nerves/ mm2 while the mean density of the peripheral endplate was 0.10 (SEM 0.03) nerves/ mm2 (p= 0.0001). There was no significant difference between the overall endplate and annulus innervation densities 0.52 (SEM 0.1) v 0.37 (SEM 0.07) p=0.2. But the peri-annular connective tissue, external to the outer annulus contained the densest innervation of any region in the motion segment 1.05 (SEM 0.16).
Discussion: The lumbar intervertebral disc has a meagre innervation. This is concentrated in the peri-annular connective tissue and the central endplate. While receptor threshold is more closely related to nociceptive function than innervation density, these findings have important implications for any treatment of discogenic pain.
The abstracts were prepared by Dr Robert Moore. Correspondence should be addressed to him at Spine Society of Australia, c/o the Adelaide Centre for Spinal Research, Institute of Medical and Veterinary Science, PO Box 14, Rundle Mall, Adelaide SA 500, Australia.
