Origin of the radial nerve branch innervating the brachialis muscle.

The brachialis muscle is dually innervated by the musculocutaneous nerve running via the anterior division of the brachial plexus and the radial nerve running via the posterior division of the plexus. There have been inconsistent descriptions of the pathway of the radial nerve branch at the brachial plexus. This study investigated the route of the radial nerve branch innervating the brachialis muscle at the brachial plexus. In 20 samples, the radial nerve branch innervating the brachialis muscle was separated and traced up to the cervical nerve under a surgical microscope. All the radial nerve branches innervating the muscle ran via the posterior cord, the posterior division, and the superior or middle trunk at the brachial plexus. The radial nerve branches arose from C5 in 5 cases, C6 in 11 cases, C5 and C6 in 3 cases, and C6 and C7 in 1 case.