Gender, BMI and side-to-side differences in spinal accessory nerve conduction from the upper and middle components of the trapezius muscle.

Introduction: There is a variety of testing methods described in the literature for the spinal accessory nerve (SAN). This study aims to evaluate side-to-side, gender, and BMI differences with surface recording from the upper and middle trapezius using a standard distance to the upper trapezius.

Methods: Subjects underwent bilateral SAN conduction testing with the active recording electrodes over the superior border of the upper trapezius, midway between the acromion and the C7 spinous process, and over the middle trapezius 3 cm medial to the vertebral border of the scapula.