Muscular branches of radial nerve

At a glance

English

Muscular branches of radial nerve

Latin (TA2)

Rami musculares nervi radialis

System

Nerve

Region

Upper limb

Side

Paired, left and right

About the muscular branches of radial nerve

Before it divides into its superficial and deep branches near the elbow, the radial nerve gives a set of muscular branches to the back of the arm and the lateral side of the elbow. They are usually grouped by where they leave the nerve: medial branches in the axilla and upper arm, posterior branches in the radial groove, and lateral branches above the lateral epicondyle. Together they carry fibres mainly from C6 to C8.

The medial muscular branches arise on the inner side of the arm, high up. One goes to the long head of triceps, although in some people that head is supplied by the axillary nerve instead. A long, thin branch to the medial head of triceps runs down close beside the ulnar nerve into the lower arm, which is why it has been called the ulnar collateral nerve. The posterior muscular branch is a stout stem that leaves the radial nerve as it lies in the groove between triceps and the humerus. It splits into filaments for the lateral and medial heads of triceps, and a slender twig that descends within the medial head to reach anconeus behind the elbow.

The lateral muscular branches arise after the radial nerve has pierced the lateral intermuscular septum to enter the front of the arm, where it lies in the groove between brachialis and brachioradialis. They supply brachioradialis, a small lateral part of brachialis, and extensor carpi radialis longus, which is otherwise a musculocutaneous muscle. The branch to extensor carpi radialis brevis usually comes from the deep branch instead.

Since these branches leave the nerve at different levels, the site of a radial nerve injury can be judged by which muscles still work. A lesion in the axilla, such as crutch palsy, weakens triceps as well as the wrist and finger extensors. With a fracture of the humeral shaft, the branches to triceps have often already left the nerve, so elbow extension is kept while the wrist drops. Injury just below the elbow leaves extensor carpi radialis longus and brachioradialis working, so the wrist can still be lifted, though it drifts towards the radial side.

Course and supply

Arises from

Arise from the radial nerve in the axilla, in the radial groove of the humerus, and above the lateral epicondyle before the nerve divides.

Ends in

End in triceps brachii and anconeus behind, and in brachioradialis, the lateral part of brachialis and extensor carpi radialis longus in front.

Supplies

Motor to triceps and anconeus for elbow extension, to brachioradialis for elbow flexion in mid-pronation, and to extensor carpi radialis longus for wrist extension and radial deviation.