Radial nerve

The radial nerve is a mixed motor and sensory nerve of the arm that arises from the Brachial plexus and is involved in the innervation of the muscles of the upper and forearm.

Anatomical course

The radial nerve arises from the posterior cord of the brachial plexus. It contains nerve fibers from segments C5 to C8 and Th1. Along its course, the radial nerve runs together with the profunda brachii artery through the triangular interval and then continues in the radial canal, or radial groove, around the dorsal aspect of the humerus. It pierces the lateral intermuscular septum of the arm approximately 10 cm proximal to the lateral epicondyle of the humerus. Together with the radial collateral artery, it runs in the lateral bicipital groove and passes through the radial tunnel into the cubital fossa. There, it gives off muscular branches to the brachioradialis muscles and divides into a motor deep branch and a sensory superficial branch.

Deep branch

The motor deep branch travels along the dorsal aspect of the forearm through the supinator muscle and enters the extensor compartment of the forearm, continuing from there to the hand. Its deep terminal branch is called the posterior interosseous nerve.

Superficial branch

The sensory superficial branch follows the brachioradialis muscle and runs in the radial groove of the forearm alongside the radial artery. In the distal third of the forearm, it passes beneath the tendon of the brachioradialis muscle and thus reaches the extensor aspect. There, it anastomoses with branches of the dorsal branch of the ulnar nerve. At its terminal course, the superficial branch divides into 5 dorsal digital nerves, which supply the skin on the dorsal aspect of the radial 2 1\/2 digits.

Function

The radial nerve innervates the muscles primarily on the dorsal aspects of the upper arm and forearm, including the extensors, as well as the long muscles of the hand. In addition, the nerve is responsible for sensory innervation of the skin on the dorsal and lateral aspects of the arm.

Clinical relevance

• A lesion of the radial nerve is referred to as radial nerve palsy. The following types are distinguished according to the location of the lesion:

• High radial nerve palsy

• Intermediate radial nerve palsy

• Low radial nerve palsy

• High radial nerve palsy results in paralysis of the entire extensor musculature of the arm and hand. This is particularly manifested by flaccid wrist drop (Wrist drop).

• Low radial nerve palsy results from compression of the radial nerve in the supinator compartment and is also referred to as supinator tunnel syndrome.

• An injury to the sensory superficial branch causes Wartenberg syndrome.