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/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 and preliminary normative data was established. The incidence of deep branch LPN/tibial nerve 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, since the standard recording site is the abductor digiti minimi (ADM). It is possible that selective deep branch involvement may occur, and if so, recording from the FDI may prove valuable.
