The accessory nerve controls the sternocleidomastoid and trapezius muscles which have some of the following functions: rotation of head away from side of the contracting sternocleidomastoid muscle, titling the head, flexion of the neck, elevation of the shoulder by the trapezius, and drawing the head back so the face is upward. Injury to the accessory nerve will result in impaired function of the shoulder.
Accessory nerve damage medical expert witness specialties include neurosurgery, orthopaedic spine surgery, neurology, and head and neck surgery.