Nerve Ingrowth into Intervertebral Disc in Internal Disc Disruption

Abstract

Study Design: The ingrowth of the nociceptive nerve ending into intervertebral disc was examined using immunohistochemistry and quantified using western blotting. Objectives: To determine if the nociceptive nerve innervates into the intervertebral discs of internal disc disruption (IDD). Summary and Literature Review: Nociceptive nerve ending and vessel ingrowth into intervertebral disc is associated with IDD and HNP. Substance P is a neurotransmitter that is found in the nociceptive nerve endings. Immunohistochemistry has confirmed the presence, and western blot has isolated the target. The localization of novel nociceptive innervation, and a quantitative comparison was made according to the original pathology is of interest. Materials and Methods: 10 specimens of intervertebral disc were collected from IDD during total disc replacement surgery , and another 10 specimens of intervertebral disc from HNP were collected during discectomy. The control samples of intervertebral disc were obtained from 3 adolescent patients with idiopathic scoliosis, and 2 patients with a lumbar bursting fracture. Standard immunohistochemical techniques were used to test for the nociceptive neurotransmitter (substance P), which is a protein expressed during axonogenesis (growth-associated protein 43, GAP43), and a general nerve marker (protein gene produce 9.5, PGP9.5). The expression of substance P protein was quantified using western blot for its polyclonal antibody. Results: In IDD (n=10), substance P was expressed in 6 cases of outer annulus fibrosus (AF), 5 cases of inner AF, and 3 cases of nucleus pulposus (NP). In HNP (n=10), substance P was expressed in 4 cases of outer AF, 3 cases of inner AF, and 2 cases of NP. In the control group, only 2 cases expressed substance P in outer AF. GAP43 was only positive in outer AF as follows: IDD 3 cases, HNP 1 case, and control 1 case. None of the specimens showed localized PGP 9.5. Substance P was localized significantly in larger quantities in IDD than in the control group (p=0.002). In HNP, the expression level was larger than the control and lower than the IDD group but this was not statistically significant (p=0.158, p=0.108). Conclusions: Innervation of nociceptive nerve endings was identified at the degenerative intervertebral disc of IDD, which may contribute to back pain.