NEURAL CONNECTION BETWEEN THE VENTRAL PORTION OF THE LUMBAR INTERVERTEBRAL DISC AND THE GROIN SKIN

This study was designed to investigate neural mechanisms of referred p ain in lumbar intervertebral disc lesions. Patients with a degenerativ e disc in lower lumbar segments occasionally complain of groin pain, w hich cannot be explained anatomically as having a radicular origin. In rats pretreated with intravenous application of Evans blue dye, the d ye extravasation appeared in the groin skin after application of capsa icin to the ventral portion of the L5-6 intervertebral disc. This resp onse occurred even in rats with a sectioned L-5 spinal nerve and sympa thetic trunks, but did not occur in rats with a sectioned genitofemora l nerve. Capsaicin topically applied to the sciatic nerve did not caus e dye extravasation in the hindpaw. Therefore, groin dye extravasation was not due to a direct effect of capsaicin but, rather, presumably w as caused by an ''antidromic axon reflex'' of dichotomizing C fibers o r to a segmental sympathetic reflex causing vascular permeability. The present results indicate that the ventral portion of the lumbar discs is neurally connected to the groin skin via the upper (L-2) lumbar sp inal nerves in rats. Groin pain coincident with low-back pain may be e xplained as referred pain, indicating that a lesion is present in the ventral portion of the lumbar intervertebral disc space.