Radial Nerve Palsy

Definition & Cause

Radial nerve palsy produces the classic ‘wrist drop’. The radial nerve is commonly injured where it winds round the spiral (radial) groove of the humerus — hence its association with a fracture of the shaft of the humerus — and by prolonged pressure (‘Saturday-night palsy’, from the arm hanging over a chair) and crutch pressure.

Clinical Features

The radial nerve supplies the extensors of the wrist and fingers, so its paralysis causes wrist drop — inability to extend the wrist, metacarpophalangeal joints and thumb — with weak grip (because the wrist cannot be stabilised in extension). Sensory loss is over a small area of the dorsal first web space. If the lesion is above the elbow, the triceps may also be affected; the brachioradialis and supinator are involved with high lesions.

Management

A radial palsy accompanying a closed humeral shaft fracture is usually a neurapraxia and recovers spontaneously over weeks to a few months, so it is observed with a cock-up wrist splint (to hold the wrist extended and keep the hand functional) and physiotherapy while awaiting recovery. Failure to recover, or a nerve divided by an open injury, requires exploration and repair; late irrecoverable cases are treated by tendon transfers.

Complications & Recovery

Because the radial-groove palsy that accompanies a humeral shaft fracture is usually a neurapraxia, an advancing Tinel’s sign and return of brachioradialis and wrist-extensor power over subsequent weeks herald recovery, and nerve conduction studies help confirm the trend. During the waiting period the hand is kept functional and the joints supple with a cock-up splint and exercises; the main pitfall is allowing a fixed flexion contracture of the wrist and fingers to develop while the extensors are paralysed.

Brachioradialis involvement localises the lesion above the elbow.

• Radial nerve palsy = wrist drop; injured at the spiral groove (humeral shaft fracture, ‘Saturday-night palsy’).
• Loss of wrist/finger/thumb extension; sensory loss at the dorsal first web space.
• Closed fracture palsy usually neurapraxia → recovers; splint (cock-up) and observe.
• Open division → repair; irrecoverable → tendon transfers.