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Describe the course of the radial nerve and the effects of its injury at different levels.

Anatomy · 1st Professional — Pre-Clinical

The radial nerve (C5–T1) is the largest branch of the brachial plexus, arising from the posterior cord.

In the arm — triceps (all three heads), anconeus, brachioradialis, extensor carpi radialis longus, and part of brachialis
In the forearm (via posterior interosseous) — supinator, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, abductor pollicis longus, extensors pollicis longus and brevis, extensor indicis
It supplies NO muscle in the hand
Mnemonic — "best" muscles: Brachioradialis, Extensors, Supinator, Triceps

Site	Cause	Effects
Axilla	Crutch palsy; dislocation of the shoulder; "Saturday night palsy" with the arm over a chair	Loss of elbow extension (triceps) plus wrist drop and sensory loss
Spiral groove	Mid-shaft fracture of the humerus; the commonest site	Wrist drop; triceps spared (its branches arise higher); sensory loss confined to the dorsal web space
Elbow / forearm	Fracture of the neck of the radius; supinator (arcade of Frohse) compression	Posterior interosseous palsy — finger drop with NO sensory loss; wrist extension partly preserved
Wrist	Tight handcuffs or watch strap — "cheiralgia paraesthetica"	Sensory loss only

Inability to extend the wrist and the metacarpophalangeal joints, so the hand hangs limply
Grip is markedly weakened, because the long flexors cannot act efficiently without the wrist being stabilised in extension — the synergistic action of the extensors
Interphalangeal extension is retained, by the lumbricals and interossei (median and ulnar supplied)
Supination is weak but not lost, since biceps still acts

Confined to a small area over the first dorsal interosseous space (the anatomical snuffbox region)
The sensory loss is far less than the extensive motor loss, because of overlap from the median and ulnar territories
The dorsum of the lateral three and a half digits is supplied, excluding the nail beds, which are median territory

The radial nerve must be tested in every mid-shaft humeral fracture — before and after reduction; most such palsies are neurapraxia and recover
Saturday night palsy — the nerve compressed against the humerus by the arm hanging over a chair during deep sleep, classically after alcohol
Crutch palsy — a crutch pressing in the axilla; prevented by ensuring weight is taken on the hands
A cock-up splint holds the wrist extended and restores useful grip while the nerve recovers
Posterior interosseous palsy spares sensation entirely, which distinguishes it clinically from a higher radial lesion

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