Motor-Evoked Potentials of the Abductor Hallucis Muscle and Their Relationship with Foot Arch Functional Anatomy

Background: The present study aimed to investigate the correlation between abductor hallucis (AH) muscle motor evoked potential (MEP) amplitude and foot arch anatomy. Methods: Twelve healthy individuals underwent foot arch measurement using a digital photographic technique and measurements of cortical excitability using transcranial magnetic stimulation applied on the cortical representation area of the right AH muscle. Truncated foot length and dorsal height were then measured and used to create the arch height index (AHI). Resting motor threshold, MEP amplitude (using a stimulation intensity of 110% resting motor threshold), and cortical silent period duration were also measured. Results: Mean ± SE values were as follows: truncated foot length, 16.72 ± 0.3 cm; dorsal height, 5.62 ± 0.13 cm; AHI, 0.34 ± 0.01; resting motor threshold, 81.6% ± 2.12%; MEP amplitude, 0.71 ± 0.1 mV; and cortical silent period duration, 108.05 ± 0.45 msec. A significant correlation was found between MEP amplitude and AHI (Spearman's rho: P < .01). Conclusions: These results indicate that AH muscle functional neuroanatomy measurements are reliable and might be used by clinicians and therapists to investigate foot arch physiology and monitor the efficacy of treatments and rehabilitative protocols.