Electrophysiologic mapping and cadaveric dissection of the lateral foot: Implications for tibial motor nerve conduction studies

Objective: To clarify, through electrophysiologic mapping and cadaveric dissection of the lateral foot, the previously published "proximal" and "distal" recording sites for tibial motor nerve conduction studies. Design: Observational. Setting: Electromyography laboratory; anatomy laboratory. Patients or Other Participants: Ten asymptomatic feet; eight cadaveric feet. Main Outcome Measures: (1) Amplitudes and onset latencies of compound muscle action potentials (CMAPs) recorded over a grid on the lateral foot that included the "proximal" and "distal" recording sites; (2) nerve supply and anatomic boundaries of the abductor digiti minimi pedis (ADMP) and nearby muscles, particularly as they relate to the above recording sites. Results: (1) Relatively large CMAPs were recorded at and around the "proximal" and "distal" sites, with significantly shorter "proximal" latencies. (2) In all cadaveric feet, ADMP was innervated by only the inferior calcaneal nerve (ICN) and was located deep to the "proximal" site, with virtually no muscle fibers deep to the "distal" site. The flexor digiti minimi brevis (FDMB) was conspicuously located immediately deep to the "distal" site and was innervated by only the lateral plantar nerve (LPN), Conclusions: This study strongly suggests that the "proximal" site records predominantly from the ICN-innervated ADMP, whereas the "distal" site predominantly records from the LPN-innervated FDMB, (C) 1998 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation.