Electrophysiological Differentiation Between Muscle and Sensory Nerve Funiculi for Peripheral Nerve Repair

Summary

The purpose of this investigation was to differentiate the muscle funiculi from the sensory funiculi in the proximal stump of the peripheral nerve. Five cats anesthetized with sodium pentobarbital were used. An epidural electrode was inserted under the C7 lamina and needle electrodes were inserted at disc spaces C2–3, C3–4, C4–5 and C5–6. The amplitude of cortical somatosensory evoked potential (SEP) induced by stimulation of the superficial radial nerve, which has a sensory function, was usually larger than that of the deep radial nerve, which has a motor function. When a stimulus of less than 1.9 mA was applied through the needle electrode at the C5-6 disc space, a spike component suggesting orthodromic passage along the motor fibers was observed only from the muscle nerve. More intense stimulation (5.7 mA) under C7 lamina elicited two components from the sensory branch. The second component was almost completely abolished after intravenous injection of 0.5 mg/kg picrotoxin, hence it was considered to be the dorsal root reflex. Especially at C4–5 and C5–6 disc spaces, the amplitude of the positive component subsequent to the first negative component upon stimulation of the sensory nerve was higher than that following stimulation of the muscle nerve. These experiments may be clinically applicable to surgery of the funicular suture.