The radial nerve originates from the C5 to T1 roots. These nerve fibers travel along the upper, middle, and lower trunks. They continue as the posterior cord and terminate as the radial nerve.

The radial nerve is prone to entrapment in the axilla (crutch palsy), the upper arm (spiral groove), the forearm (posterior interosseous nerve), and the wrist (cheiralgia paresthetica). Radial neuropathies can result from direct nerve trauma, compressive neuropathies, neuritis, or complex humerus fractures [1].

In the proximal arm, the radial nerve gives off three sensory branches (posterior cutaneous nerve of the arm, lower lateral cutaneous nerve of the arm, and posterior cutaneous nerve of the forearm). The radial nerve supplies a motor branch to the triceps and anconeus before wrapping around the humerus in the spiral groove, a common site of radial nerve injury. The nerve then supplies motor branches to the brachioradialis, the long head of the extensor carpi radialis, and the supinator. Just distal to the lateral epicondyle, the radial nerve divides into the posterior interosseous nerve (a motor nerve) and the superficial sensory nerve (a sensory nerve). The posterior interosseous nerve supplies the supinator muscle and then travels under the arcade of Frohse (another potential site of compression) before coursing distally to supply the extensor digitorum communis, extensor digiti minimi, extensor carpi ulnaris, abductor pollicis longus, extensor pollicis longus, extensor pollicis brevis, and extensor indicis proprius. The superficial sensory nerve supplies sensations to the dorsum of the hand, excluding the fifth and ulnar half of the fourth digit, which is supplied by the ulnar nerve (Fig. 26.1). Radial neuropathy is relatively uncommon compared with other compressive neuropathies of the upper limb. A study in 2000 showed that the annual age-standardized rates per 100,000 of new presentations in primary care were 2.97 in men and 1.42 in women for radial neuropathy, 87.8 in men and 192.8 in women for carpal tunnel syndrome, and 25.2 in men and 18.9 in women for ulnar neuropathy [2].

f26-01-9781455775774 — FIGURE 26.1 Neural branching of the radial nerve. Its origin in the axilla to the termination of its motor and sensory branches is shown. The inset demonstrates the cutaneous distribution of the various sensory branches of the radial nerve. (From Haymaker W, Woodhall B. Peripheral Nerve Injuries. Philadelphia, WB Saunders, 1953.)

Symptoms

Symptoms of radial neuropathy depend on the site of nerve entrapment [3] (Table 26.1). In the axilla, the entire radial nerve can be affected. This may be seen in crutch palsy if the patient is improperly using crutches in the axilla, causing compression. With this type of injury, the median, axillary, or suprascapular nerves may also be affected. All radially innervated muscles (including the triceps) as well as sensation in the posterior arm, forearm, and dorsum of the hand may be affected.

Table 26.1

Extensor Tendon Compartments—Wrist

Muscles	Insertion	Evaluation
Abductor pollicis longus	Dorsal base of thumb metacarpal	Bring thumb out to side
Extensor pollicis brevis	Proximal phalanx of the thumb
Extensor carpi radialis longus Extensor carpi radialis brevis	Dorsal base of index and middle metacarpals	Dorsiflex the wrist with the hand in a fist and apply resistance radially
Extensor pollicis longus	Distal phalanx of the thumb	Hand flat on table Lift only thumb
Extensor digitorum communis	Extensor hood and base of proximal phalanges of the ulnar four digits	Extend fingers with wrist in neutral
Extensor indicis proprius		Extend index finger
Extensor digiti minimi	Proximal phalanx of the little finger	Straighten little finger with other fingers in fist
Extensor carpi ulnaris	Dorsal base of the fifth metacarpal	Wrist extension with ulnar deviation

From American Society for Surgery of the Hand. The Hand: Examination and Diagnosis. New York, Churchill Livingstone, 1983.

The radial nerve is especially prone to injury in the spiral groove (also known as Saturday night palsy or honeymooner’s palsy). Symptoms include weakness of all radially innervated muscles except the triceps and sensory changes in the posterior arm and hand. In the forearm, the radial nerve is susceptible to injury as it passes through the supinator muscle and the arcade of Frohse. Because the superficial radial sensory nerve branches before this area of impingement, sensation will be spared. The patient will complain of weakness in the wrist and finger extensors. On occasion, the superficial radial sensory nerve is entrapped at the wrist, usually as a result of lacerations at the wrist or a wristwatch that is too tight. In this situation, the symptoms will be sensory, involving the dorsum of the hand.

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