Radial nerve

The radial nerve is a major peripheral nerve of the upper limb in humans. It is a component of the brachial plexus, arising from the posterior cord and receiving contributions primarily from the ventral rami of spinal nerves C5, C6, C7, C8, and T1. The nerve is responsible for innervating the extensor musculature of the arm and forearm and for providing sensory innervation to the posterior aspect of the upper limb.

Anatomical Course

1. Origin: The radial nerve originates from the posterior cord of the brachial plexus within the axilla.
2. Axillary Region: It descends posterior to the axillary artery and pierces the lateral intermuscular septum to enter the posterior compartment of the arm.
3. Arm: It travels within the radial (spiral) groove of the humerus, situated between the lateral and medial supracondylar ridges. In this region it supplies the triceps brachii and anconeus muscles.
4. Elbow: At the lateral epicondyle of the humerus the nerve passes anterior to the lateral collateral ligament, then divides into a superficial (sensory) branch and a deep (motor) branch (the posterior interosseous nerve).
5. Forearm: The deep branch pierces the supinator muscle to become the posterior interosseous nerve, which innervates the majority of the extensor muscles of the wrist and fingers. The superficial branch descends subcutaneously along the lateral aspect of the forearm, providing cutaneous sensation to the dorsal hand.

Motor Functions

• Arm: Triceps brachii (all heads) and anconeus.
• Forearm: Brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, extensor pollicis longus and brevis, abductor pollicis longus, supinator (via deep branch), and other smaller extensors.

Sensory Distribution

• Cutaneous: The radial nerve supplies skin over the posterior arm, posterior forearm, and the dorsal surface of the lateral (radial) three and one‑half digits, excluding the nail beds.
• Joint Proprioception: Provides proprioceptive input from the elbow, wrist, and hand joints.

Clinical Significance

• Radial Nerve Palsy: Injury to the radial nerve can result in weakness or loss of wrist, finger, and thumb extension, producing the characteristic “wrist drop.” Common causes include humeral shaft fractures, compression from prolonged immobilization (“Saturday night palsy”), and iatrogenic injury during surgical procedures.
• Posterior Interosseous Syndrome: Isolated motor deficit of the deep branch without sensory loss, typically due to compression within the supinator tunnel.
• Neurological Examination: Function is assessed by testing extension of the elbow (triceps), wrist (radial deviation), metacarpophalangeal joints, and thumb, as well as sensation over the dorsum of the hand.

Variations and Anatomical Notes

• Although the radial nerve generally receives fibers from C5–T1, variations in the exact spinal levels contributing to the nerve have been reported, with occasional contributions from C4 or absence of C5 fibers.
• The superficial branch may exhibit variable branching patterns on the dorsal hand, influencing the distribution of cutaneous innervation.

References (selected)

• Standring, S. (Ed.). Gray's Anatomy: The Anatomical Basis of Clinical Practice (42nd ed.). Elsevier, 2020.
• Moore, K. L., Dalley, A. F., & Agur, A. M. R. Clinically Oriented Anatomy (8th ed.). Wolters Kluwer, 2019.
• Calfee, R. P., & Saha, J. “Radial Nerve Injuries: A Review of Current Concepts.” Journal of Hand Surgery, vol. 45, no. 4, 2021, pp. 283‑291.