Learning Objectives

By the end of this topic, the learner will be able to:

1. Identify the spinal root values of the radial nerve.
2. Trace its anatomical course from the axilla to the hand.
3. Describe its motor and sensory functions.
4. Recognize the clinical features of radial nerve injury at different levels.

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Overview

The radial nerve is the major nerve of the posterior compartments of the arm and forearm.

• Roots: C5–T1
• Motor: Triceps brachii and all extensor muscles of the forearm
• Sensory: Posterior arm, posterior forearm, lateral dorsum of the hand, and dorsal surface of the lateral 3½ digits

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Anatomical Course

The radial nerve is the terminal continuation of the posterior cord of the brachial plexus (C5–T1).

• It arises in the axilla, posterior to the axillary artery.
• It exits the axilla through the triangular interval and supplies the long and lateral heads of the triceps brachii.
• It then runs in the radial (spiral) groove on the posterior surface of the humerus, where it supplies the medial head of triceps.
• The nerve wraps laterally around the humerus, accompanied by the deep brachial artery.
• It passes anterior to the lateral epicondyle and enters the cubital fossa.
• At the level of the elbow, it divides into:

Terminal Branches

• Deep branch (motor): Innervates the extensor muscles of the posterior forearm.
  • After piercing the supinator, it is renamed the posterior interosseous nerve.
• Superficial branch (sensory): Supplies the dorsal surface of the lateral hand and fingers.

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Motor Functions

Arm

• Triceps brachii (all three heads) – elbow extension
• Brachioradialis – elbow flexion in mid-pronation
• Extensor carpi radialis longus – wrist extension and abduction

Forearm

The deep branch (posterior interosseous nerve) innervates all remaining extensors and supinators, producing:

• Wrist extension
• Finger and thumb extension
• Forearm supination

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Sensory Functions

Four cutaneous branches provide sensation:

• Lower lateral cutaneous nerve of the arm – lateral arm
• Posterior cutaneous nerve of the arm – posterior arm
• Posterior cutaneous nerve of the forearm – posterior forearm
• Superficial branch – dorsum of the lateral 3½ digits and hand

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Clinical Relevance – Radial Nerve Injury

In the Axilla

Cause: Shoulder dislocation, proximal humerus fracture, crutch palsy

• Motor: Loss of elbow, wrist, and finger extension → wrist drop

• Sensory: Loss over the posterior arm, posterior forearm, and dorsum of the lateral 3½ digits

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In the Radial Groove

Cause: Mid-shaft humeral fracture

• Motor: Triceps largely spared, but wrist and finger extension lost → wrist drop
• Sensory: Loss over the dorsum of the lateral hand and digits

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In the Forearm