History
Symptoms are dependent on the site of the lesion. The onset of symptoms may be acute or insidious. Patients may present acutely with upper limb sensory and/or motor deficits depending on the site of injury and progress to more long-term complications including mild-to-severe hand deformities. The most common reported symptom is wrist drop.
Axilla lesions:
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Weakness of all radial-innervated muscles (wrist drop and loss of triceps and brachioradialis reflexes)
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Sensation loss in the dorsum of the arm
Arm lesions:
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Weakness of radial-innervated muscles with sparing of arm extension if the lesion is at or distal to the spiral groove as the motor branch to the triceps branches off before the humerus midshaft
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If the lesion is high above the elbow, then numbness of the forearm and hand may be an additional symptom
Forearm lesions
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Sensation typically is spared despite the wrist drop
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Pain in the forearm resembling tennis elbow may be prominent
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This presentation is initially acute for several days to weeks
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If the lesion is at the wrist, patients report isolated sensory changes and paresthesias over the back of the hand without motor weakness
Wrist lesions
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If the lesion is at the wrist, patients report isolated sensory changes and paresthesias over the back of the hand without motor weakness
Physical
Radial neuropathy typically presents with weakness of wrist dorsiflexion (ie, wrist drop) and finger extension.
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If the lesion is in the axilla, all radial-innervated muscles are involved.
The triceps and brachioradialis reflexes are decreased
Sensation is decreased occur over the triceps, the posterior part of the forearm, and dorsum of the hand
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Acute compression of the radial nerve commonly occurs at the spiral groove. If the lesion is at this level, all radial-innervated muscles distal to the triceps are weak.
Triceps reflex is preserved, but brachioradialis is decreased
Sensory loss occurs over the radial dorsal part of the hand and the posterior part of the forearm
Numbness over the triceps area is variable
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In isolated posterior interosseous lesions, sensation is spared and motor involvement occurs in radial muscles distal to the supinator.
Brachioradialis reflex is intact
The extensor carpi radialis sometimes is also spared, resulting in radial deviation with wrist extension
Pain may occur with palpation at the proximal forearm and with forceful supination
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In distal radial sensory lesions at the wrist, no motor weakness occurs. Numbness of the dorsal hand is noted, sparing the fifth digit.
Causes
See the list below:
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Penetrating trauma can cause injury anywhere along the nerve.
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Compressive lesions high in the axilla can occur from improper use of crutches.
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Compression injuries at the humeral spiral groove occur in patients with sustained compression of this area over a period of several hours. [15]
Reported in patients who fall asleep in a drunken or drug-induced stupor with an arm over a chair and in honeymooners.
Results from fracture of the humerus that leads to compression or secondary laceration of the nerve as it wraps around the humerus near the spiral groove. [16]
Reported in wheelchair users, when the spiral groove of the humerus is compressed on a hard wheelchair surface. [17]
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Subluxation of the radius can produce radial nerve injury in the proximal forearm.
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The posterior interosseous syndrome typically occurs from compression of this division of the radial nerve as it penetrates the supinator muscle within the proximal forearm. [18]
Associated with repetitive supination of the forearm and hypertrophy of the supinator muscle.
Can occur secondary to elbow synovitis, ganglion cysts [19] , enlarged bursa from the elbow, or tumors (especially lipomas at the entry of the radial nerve into the supinator muscle).
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Isolated distal sensory radial neuropathy is associated with compression from handcuffs and tight bracelets.
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Bilateral radial palsies suggest lead intoxication. Lead exposure may be occupational. [20]
Complications
Complications may include:
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Partial or complete loss of sensation in hand
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Partial or complete loss of motor function in hand
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Upper limb muscle atrophy
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Upper limb joint contractures and deformities
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The Radial Nerve from Gray's Anatomy (published 1918, public domain, copyright expired).
