Does the Location of the Motor Point Identified with Electrical Stimulation Correspond to that Identified with the Gross Anatomical Method?

Abstract

[Purpose] The purpose of this study was to determine whether the location of the motor point (MP) identified with the gross anatomical method corresponds with that identified with electrical stimulation in the tibialis anterior muscle (TA) in order to test the validity of adopting the nerve entry point as the target for electrical stimulation. [Subjects] We used 16 lower limbs from 12 cadavers and 26 lower limbs from 13 healthy adults. [Methods] We identified the location where the thickest motor nerve entered the muscle belly of TA in cadavers as the anatomical MP and where the surface electrical stimulation threshold of TA was lowest in healthy adults as the electrical MP. We defined the line connecting the fibular head and the lateral malleolus as the reference line and drew a line perpendicular to this that intersected the MP. We measured each MP as the length from the fibular head to the perpendicular line, and expressed this as a proportion of the reference line length. The distribution of each MP was compared. [Results] There was significant unequal variance between the two types of MP. The electrical MP was significantly more distal than the anatomical MP. [Conclusion] The anatomical MP does not appear to correspond to the electrical MP, hence adopting the nerve entry point as the target of electrical stimulation is inappropriate.