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 pain in lumbar intervertebral disc lesions. Patients with a degenerative disc in lower lumbar segments occasionally complain of groin pain, which cannot be explained anatomically as having a radicular origin. In rats pretreated with intravenous application of Evans blue dye, the dye extravasation appeared in the groin skin after application of capsaicin to the ventral portion of the L5-6 intervertebral disc. This response occurred even in rats with a sectioned L-5 spinal nerve and sympathetic trunks, but did not occur in rats with a sectioned genitofemoral nerve. Capsaicin topically applied to the sciatic nerve did not cause dye extravasation in the hindpaw. Therefore, groin dye extravasation was not due to a direct effect of capsaicin but, rather, presumably was caused by an "antidromic axon reflex" of dichotomizing C fibers or 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 spinal nerves in rats. Groin pain coincident with low-back pain may be explained as referred pain, indicating that a lesion is present in the ventral portion of the lumbar intervertebral disc space.