New method to perform medial plantar proper digital nerve conduction studies

Abstract

We describe a technique that records the sensory nerve action potential (SNAP) of the medial plantar proper digital nerve (MPPDN), which is the final sensory branch of the medial plantar nerve. We obtained antidromic MPPDN responses from 118 healthy volunteers, with surface recording electrodes placed on the medial side of the first metatarsal head of the great toe, with electrical stimulation applied at the 40% distance of the heel to great toe reference line. Antidromic SNAP parameters were recorded and normative reference values were obtained. The stimulation site that corresponded to 40% of the reference line was located at a mean distance of 8.7+/-1.2 cm from the recording electrodes. MPPDN responses were easily obtained in all but 9 limbs. The mean SNAP amplitudes obtained by our technique were 16.1+/-6.7 microV, and the lower and upper range values were 6.4 microV and 34.4 microV, respectively. Antidromic stimulation of the MPPDN at a distance of 8-10 cm from the medial side of the first metatarsal head of the great toe yields in reliable SNAP responses. This technique should be useful in the evaluation of the MPPDN involvement in Joplin's neuroma.