Ultrasound-guided superficial radial nerve block at the wrist 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 wrist or below. Ultrasound-guided superficial radial nerve block at the wrist with local anesthetic may be used to palliate acute pain emergencies, including postoperative pain, pain secondary to traumatic injuries of the distal radius, and portions of the wrist and carpal bones innervated by the distal radial nerve, as well as cancer pain, while waiting for pharmacologic, surgical, and antiblastic methods to become effective.

Ultrasound-guided superficial radial nerve block can also be used as a diagnostic tool when performing differential neural blockade on an anatomic basis in the evaluation of distal 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 wrist. This technique may also be useful in those patients suffering symptoms from compromise of the radial nerve due to cheiralgia paresthetica. Ultrasound-guided superficial radial nerve block at the wrist may also be used to palliate the pain and dysesthesias associated with stretch injuries to the distal radial nerve.

The superficial sensory branch of the radial nerve at the wrist is susceptible to trauma during surgery for de Quervain tenosynovitis or may be damaged by the wearing of too tight wrist watches or handcuffs or the placement of forearm casts that are too tight, which can compress the nerve against the radius. Entrapment neuropathy of the superficial radial nerve at the wrist is known as cheiralgia paresthetica, Wartenberg syndrome, or prisoner’s palsy and presents as pain and dysesthesias with associated numbness of the radial aspect of the dorsum of the hand to the base of the thumb (Fig. 65.1).

Physical findings associated with entrapment or trauma of the superficial radial nerve at the wrist include a positive Tinel sign over the radial nerve at the site of injury (Fig. 65.2). Decreased sensation in the distribution of the sensory branch of the radial nerve often is present although the overlap of the distribution of the lateral antebrachial cutaneous nerve in some patients may result in a confusing clinical presentation. Flexion and pronation of the wrist, as well as ulnar deviation, may elicit in the distribution of the superficial sensory branch of the radial nerve in patients suffering from cheiralgia paresthetica. A positive wristwatch test is highly suggestive of the diagnosis of cheiralgia paresthetica. The wristwatch test is performed by having the patient fully deviate his or her wrist to the ulnar side. The examiner then exerts firm pressure on the skin overlying the ulnar nerve (Fig. 65.3). The patient is then instructed to fully flex the wrist. The test is considered positive if this maneuver elicits dysesthesia, pain, or numbness.

The key landmark when performing ultrasound-guided superficial radial nerve block at the wrist is the location of the radial artery and the bony radial styloid. 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. The nerve passes into the substance of the brachioradialis muscle, and at a point just 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. 65.4).