Electrophysiologic response recorded in the first dorsal interosseous muscle with stimulation of the tibial and deep fibular nerves.

Foot intrinsic muscle innervation may demonstrate some variability. The first dorsal interosseous muscle (FDI) is innervated by the deep branch of the lateral plantar nerve (LPN) from the main trunk of the tibial nerve. Contribution from the deep fibular nerve (DFN) may also play a role in the supply of the FDI. Thirty healthy adult volunteers were studied to determine the presence and type of response in the FDI with stimulation of the tibial nerve/deep branch of the LPN and DFN. Both nerves were stimulated at the ankle and knee with a surface and needle recording from the FDI. Latency, amplitude, and conduction values were recorded for each nerve. The incidence of DFN supply to the FDI was 16.6% with a mean ankle amplitude of 152 microV. The incidence of tibial nerve/deep branch of the LPN supply to the FDI was 100%, with a mean ankle amplitude of 5.11 mV. The superficial branch of the LPN is most often studied when evaluating for tarsal tunnel syndrome because the standard recording site is the abductor digiti minimi (ADM). Recording from the ADM, however, frequently produces a less than desirable waveform, and the technical challenges encountered with this site make tarsal tunnel syndrome assessment difficult. It is also possible that selective involvement of the deep branch of the LPN may occur, and if so, recording from the FDI may prove valuable.