A loose ligature-induced mononeuropathy produces hyperalgesias mediated by both the injured sciatic nerve and the adjacent saphenous nerve

An experimental mononeuropathy was produced in rats by unilateral loose ligation of the sciatic nerve, with a contralateral sham surgery. Repeated bilateral sensory testing was performed over time to investigate any threshold differences between the loose ligature side and the contralateral control side. A prolonged reduction in the mean withdrawal threshold to heat was observed on the loose ligature side over the medial dorsum of the hindpaw (MDH), and over the plantar surface of the hindpaw (PSH). Following loose ligature there was also a significant reduction in the von Frey fiber withdrawal thresholds over the lateral dorsum of the hindpaw (LDH) and the medial dorsum of the hindpaw (MDH). In a second experiment the saphenous nerves were transected bilaterally in rats who had an earlier unilateral loose sciatic ligation. The heat hyperalgesia that had been previously observed over the MDH was abolished, and no withdrawal response could be elicited with the largest von Frey fiber over the MDH, indicating that the MDH hyperalgesia induced by sciatic loose ligature was mediated by the saphenous nerve. This adjacent neuropathic hyperalgesia (ANH) resembles the saphenous mediated ANH observed over the MDH following sciatic transection, follows the same temporal course of onset, and may share a similar pathogenesis. The heat threshold over the PSH and the pressure threshold over the LDH were unaffected by the bilateral saphenous transection, demonstrating that following loose sciatic ligation both of these thresholds are mediated by the sciatic nerve.