Radial Nerve

Overview

The radial nerve is a major peripheral nerve supplying the posterior portion of the upper limb.

Origin

It originates from the posterior cord of the brachial plexus (C5-T1), in the axilla region

• The location of the cord refers to its relation to the axillary artery – i.e. the radial nerve is posterior to the axillary artery

Course

• From the origin, the radial nerve courses on the posterior wall of the axilla (subscapularis, latissimus dorsi and teres major)
• It then exits the axilla inferiorly via the triangular interval with the profunda brachii artery in the posterior compartment, between long head of triceps and humerus.
• It then descends down the arm within a shallow depression on the surface of the humerus, known as the radial groove (or spiral groove)
• As it descends, the radial nerve wraps around the humerus laterally 
• It passes through the lateral intermuscular septa and runs between brachialis and brachioradialis, coursing anteriorly to the lateral epicondyle of the humerus
• It then enters the forearm through the cubital fossa where it divides into terminal branches.

Termination

The nerve terminates by dividing into two branches:

• Deep branch (motor) – innervates the muscles in the posterior compartment of the forearm
• Superficial branch (sensory) – contributes to the cutaneous innervation of the dorsal hand and fingers

Branches

Axilla

Supplies branches to:

• posterior cutaneous nerve of the arm
• branch to long head of triceps
• branch to medial head of triceps

Triangular Interval

• Supplies branches to the long and lateral heads of the triceps brachii

Spiral Groove

Supplies branches to:

• inferior lateral cutaneous nerve of the arm
• posterior cutaneous nerve of the forearm
• branch to lateral head of triceps
• branch to medial head of triceps and anconeus

Lateral intermuscular septa

Supplies branches to:

• Lateral brachialis
• Brachioradialis
• ECRL
• ECRB

Terminal branches

At the level of the radiohumeral joint line, it divides into terminal branches:

• Superficial sensory branch
• Deep branch/PIN
• ERCB branch

Anatomical Variants

• Medial head of triceps may instead be supplied by ulnar nerve