The radial nerve (C5, C6, C7, C8, and T1) arises from the posterior cord at the level of the coracoid process , posterior to the axillary artery and lateral cord . It exits the axilla towards the posterior arm through the lower triangular space (triangular interval ) bound by the teres major cranially, the long head of triceps medially, and the humerus laterally. The triceps branches come off the radial nerve high in the axilla. The nerve then courses in the posterior arm, in the spiral groove along with the profunda brachii vessels. It then enters the anterior compartment of the arm between the biceps brachii and triceps and then between the biceps brachii and brachioradialis . It gives off the brachioradialis, extensor carpi radialis longus and brevis (ECRL and ECRB) branches, and the posterior interosseous nerve (PIN ) and then continues as the superficial radial nerve (pure cutaneous). The PIN courses through the supinator muscle (arcade of Fröhse ) and supplies the remaining muscles of the posterior forearm. The superficial radial nerve emerges from under the brachioradialis tendon and supplies the skin of the dorsum of the hand laterally as well as the dorsum of the lateral three and a half fingers up to the middle phalanx.
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