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Portrait of Radial nerve

Anatomy · Brain & nerves

Radial nerve

The nerve of the extensors

Peripheral nerves · upper limb

The largest branch of the brachial plexus, the continuation of its posterior cord (roots C5–T1). It spirals round the back of the humerus in the radial groove, supplies the triceps and every extensor muscle of the elbow, wrist and fingers, and gives sensation to the back of the hand and thumb. Injury to it, classically from a broken humerus or from prolonged pressure on the arm, produces wrist drop.

How to spot them

  • ▸Winds round the back of the shaft of the humerus in a shallow oblique groove, accompanied by the profunda brachii artery
  • ▸Pierces the lateral intermuscular septum to lie in front of the elbow, between brachialis and brachioradialis
  • ▸Divides near the elbow into a deep motor branch and a superficial sensory branch
  • ▸Supplies muscles on the back of the arm and forearm, not the palm

What to know

The largest branch of the brachial plexus, continuing the posterior cord

Radial nerve — roots C5–T1.

Spirals round the back of the humerus in a groove, alongside the deep artery of the arm

Radial nerve — the radial (spiral) groove and profunda brachii.

A fractured shaft of the humerus can trap or cut it, leaving the wrist unable to extend

Radial nerve — wrist drop.

Sleeping with an arm over the back of a chair after a night's drinking can compress it, causing weakness of the wrist and fingers

Radial nerve — 'Saturday night palsy'.

Supplies the triceps and all the extensors of the forearm, wrist and fingers, as well as brachioradialis and supinator

Radial nerve — the extensor compartment of the limb.

Gives sensation to the web of skin between thumb and index finger on the back of the hand

Radial nerve — its autonomous zone.

Its deep terminal branch, the posterior interosseous nerve, pierces the supinator and supplies the finger extensors

Radial nerve — which is why a lesion there spares wrist extension but not the fingers.

Crutches pressing into the armpit can compress it, causing 'crutch palsy'

Radial nerve — an axillary compression injury.

Key ideas

  • The level of injury dictates the deficit: an axillary lesion paralyses the triceps as well; a mid-humeral lesion spares it because the branches leave above the groove.
  • It is a purely extensor nerve for the limb, the counterpart of the median and ulnar nerves in the flexor compartment.

Quick-fire facts

  • •Continues from the posterior cord of the brachial plexus, roots C5 to T1
  • •Passes through the triangular interval, accompanied by the profunda brachii artery, into the radial groove
  • •Supplies triceps, anconeus, brachioradialis, extensor carpi radialis longus, and via its deep branch the remaining forearm extensors and supinator
  • •Divides in the cubital fossa into the superficial radial nerve (sensory) and the deep branch, which continues as the posterior interosseous nerve
  • •Wrist drop is the classic sign of a radial nerve palsy
  • •'Saturday night palsy' is compression at the spiral groove, classically from falling asleep with the arm over a chair
  • •Supplies no intrinsic muscles of the hand
  • •The cutaneous supply of the dorsum of the lateral hand and thumb comes from the superficial radial branch

Drill it — 7 cards

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Sources