Radial Nerve

Origin

The radial nerve is the thickest branch of the brachial plexus and originates from the posterior cord of the plexus. It carries fibers from the anterior rami of the fifth, sixth, seventh, and eighth cervical and the first thoracic nerves (C5-T1).

Course

The radial nerve comes off from the posterior cord in the lower part of the axilla. Here it runs behind the third part of axillary artery while lying against the muscles of the posterior wall of the axilla, i.e., subscapularis, teres major, and latissimus dorsi muscles.

In the upper part of the arm, it descends posterolaterally (with the profunda brachii vessels) through the lower triangular space, between the shaft of the humerus, long head of triceps brachii, and teres major muscles. The nerve then enters the radial groove along with the profunda brachii vessels. It descends downwards and laterally between the lateral and medial heads of the triceps muscle, while in contact with the humerus.

In the lower part of the arm, it pierces the lateral intermuscular septum and passes into the anterior compartment of the arm to reach the cubital fossa where it lies between the brachialis muscle medially and brachioradialis and extensor carpi radialis longus muscles laterally. It terminates by dividing into superficial and deep branches.

Branches

In the axilla, the radial nerve provides two muscular branches to the long and medial heads of triceps brachii muscle, and one posterior brachial cutaneous nerve.

In the radial groove, the radial nerve provides three muscular branches (to the lateral and medial heads of triceps brachii and the anconeus muscles) and two cutaneous branches (inferior lateral brachial cutaneous nerve and posterior antebrachial cutaneous nerve). In addition, a vascular branch innervates the brachial artery.

In the cubital fossa, there are two terminal branches, namely the superficial and the deep branches. The posterior antebrachial interosseous nerve is generally considered to be a branch or continuation of the terminal deep branch of radial nerve; however, some authors use these names of these nerves interchangeably. The deep branch of radial nerve supplies the brachioradialis and extensor carpi radialis longus muscles, and then descends between the two heads of supinator muscle. Once the deep branch exits underneath the supinator muscle, it is referred to as the posterior antebrachial interosseous nerve.

The superficial branch is given off inside the cubital fossa and runs on the lateral side of the forearm accompanied by the radial artery. It then curves posteriorly to descend until it reaches the anatomical snuff box where it ends by innervating the skin on the dorsum of hand.

Supplied Structures

The radial nerve is a mixed nerve that carries both motor and sensory innervation. The motor branches of the radial nerve innervate the long and medial heads of triceps brachii muscle, anconeus muscles, brachialis (lateral half), brachioradialis, and extensor carpi radialis longus muscles. The posterior interosseous nerve provides muscular branches to extensor carpi radialis brevis, supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, extensor digitorum, extensor indicis, extensor digiti minimi, and extensor carpi ulnaris muscles.

Sensory innervation from the radial nerve serves the skin of the posterior arm (via the posterior brachial cutaneous nerve), skin of the posterior forearm (via the posterior lateral brachial cutaneous nerve and posterior antebrachial cutaneous nerve), and skin of the dorsal hand. Articular branches are given off to the elbow and wrist joints.

List of Clinical Correlates

—Radial nerve injuries (Moore, Dalley and Agur, 2013)

—Wrist drop (Preston and Shapiro, 2012)

References

Moore, K. L., Dalley, A. F. and Agur, A. M. R. (2013) Clinically Oriented Anatomy. Clinically Oriented Anatomy 7th edn.: Wolters Kluwer Health/Lippincott Williams & Wilkins.Preston, D. C. and Shapiro, B. E. (2012) Electromyography and Neuromuscular Disorders E-Book: Clinical-Electrophysiologic Correlations (Expert Consult - Online). Elsevier Health Sciences.