KNOW YOUR NERVES: THE RADIAL NERVE

Understanding the anatomy of the human body is an incredible journey. One of the most important components of our body is the nervous system, and within it, various nerves play critical roles. In this article, we will delve into the intricacies of the radial nerve, its origin, innervation, functions, and associated clinical conditions.

Origin of the Radial Nerve

The radial nerve is the terminal branch of the posterior cord of the brachial plexus, which is the largest cord. It receives input from the spinal nerve roots C5-T1. The nerve exits the axillary fossa posterior to the axillary artery and the humerus in the radial groove alongside the deep brachial artery. It then perforates between the lateral and medial triceps heads before entering the cubital fossa. From here, it divides into superficial and deep radial branches.

What does the Radial Nerve Innervate?

The radial nerve innervates several muscles in the arm including the anconeus, triceps, brachialis, extensor carpi radialis longus, and supinator. The deep branch of the radial nerve further innervates the posterior interossei, extensor digitorum, extensor digiti minimi, extensor indicis, extensor carpi ulnaris, extensor pollicis longus and brevis, and the abductor pollicis.

Additionally, it innervates the skin on the posterior and inferolateral arm, the posterior forearm, and the dorsum of the hand lateral to the axial line of digit 4.

Muscle Actions of the Radial Nerve

The radial nerve plays a significant role in various muscle actions.

• The triceps, assisted by the anconeus, are responsible for extending the arm.
• The brachioradialis assists forearm flexion most when the arm is in mid-pronation
• the supinator rotates the radius to turn the palm anteriorly/superiorly if the elbow is flexed.
• The extensor carpi radialis longus extends and abducts the wrist joint and is active while the fist is clenching. Furthermore, it stabilizes the humerus in adduction and protects against dislocation.

Radial Nerve Injuries: Clinical Pearls

Radial nerve injuries can present with varying symptoms depending on the location of the injury.

An injury to the radial nerve above the triceps can result in paralysis of the triceps, brachioradialis, and extensor muscles of the wrist and fingers. This would also lead to a loss of sensation on the posterior and inferolateral arm, posterior forearm, and the radial portion of the hand.

If the radial nerve is injured at the radial groove, the triceps would be weakened because only the medial head is affected. This condition is often referred to as a “wrist drop” as there is no wrist or finger extension due to the loss of distal radial innervation.

A deep penetrating injury to the forearm can result in injury to the deep branch of the radial nerve, leading to an inability to extend the thumb and metacarpophalangeal joint (MCP) of the other digits.

Equipped with Knowledge

Understanding the anatomy and functions of the radial nerve can provide valuable insights for healthcare professionals, students, and anyone interested in the human body. Knowledge about the radial nerve, its innervations, and potential injuries can contribute to better management and treatment of nerve-related conditions.

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Source: Clinically Oriented Anatomy; Keith L Moore et al; 8th edition