Ultrasound-guided radial nerve block at the humerus is useful in the management of the pain subserved by the radial nerve. This technique serves as an excellent adjunct to brachial plexus block and for general anesthesia when performing surgery at the elbow or below. Ultrasound-guided radial nerve block at the humerus with local anesthetic may be used to palliate acute pain emergencies, including postoperative pain, pain secondary to traumatic injuries of the radius, and cancer pain, while waiting for pharmacologic, surgical, and antiblastic methods to become effective (Figs. 43.1 and 43.2).

Ultrasound-guided radial nerve block can also be used as a diagnostic tool when performing differential neural blockade on an anatomic basis in the evaluation of upper extremity pain as well as in a prognostic manner to determine the degree of neurologic impairment the patient will suffer when destruction of the radial nerve is being considered or when there is a possibility that the nerve may be sacrificed during surgeries in the anatomic region of the radial nerve at the level of the humerus. This technique may also be useful in those patients suffering symptoms from compromise of the radial nerve due to radial tunnel syndrome. Ultrasound-guided radial nerve block at the humerus may also be used to palliate the pain and dysesthesias associated with stretch injuries to the radial nerve.

The key landmark when performing ultrasound-guided radial nerve block at the humerus is the point at which the radial nerve travels sandwiched between the intermuscular septum separating the bellies of the brachialis and brachioradialis muscles (Fig. 43.3). Arising from fibers from the
C5-T1 nerve roots of the posterior cord of the brachial plexus, the radial nerve passes through the axilla lying posterior and inferior to the axillary artery. As the radial nerve exits the axilla, it passes between the medial and long heads of the triceps muscle and then curves across the posterior aspect of the humerus, giving off a motor branch to the triceps muscle. Continuing its downward path, the radial nerve gives off a number of sensory branches to the upper arm as it travels in the intermuscular septum separating the bellies of the brachialis and brachioradialis muscles (see Fig. 43.3). At a point above the lateral epicondyle, the radial nerve divides into deep and superficial branches; the superficial branch continues down the arm along with the radial artery to provide sensory innervation to the dorsum of the wrist and the dorsal aspects of a portion of the thumb and index and middle fingers and the deep branch provides the majority of the motor innervation to the extensors of the forearm (Fig. 43.4).