Radial Nerve Course — OrthopaedicPrinciples.com

Courtesy: Prof Nabil Ebraheim, University of Toledo, Ohio, USA

GENERAL OVERVIEW

The radial nerve is the primary motor nerve of the posterior compartment of the arm and forearm.
It provides motor innervation to:
- The triceps brachii muscle
- The wrist and finger extensors
It also provides sensory innervation to a large portion of the dorsum of the hand.

The radial nerve descends in the arm and enters the posterior compartment.
It passes through the spiral groove (radial groove) on the posterior aspect of the humerus.
In the spiral groove, it lies:
- Between the medial head and lateral head of the triceps muscle
In this region, the nerve is particularly vulnerable in mid-shaft fractures of the humerus.

After traversing the spiral groove, the radial nerve pierces the lateral intermuscular septum.
It enters the anterior compartment of the arm, just above the elbow.
In the distal arm, it supplies motor branches to:
- Brachioradialis
- Extensor carpi radialis longus
- Extensor carpi radialis brevis

At the level of the elbow, the radial nerve divides into two terminal branches:
1. Posterior interosseous nerve (motor)
2. Superficial branch of the radial nerve (sensory)

The posterior interosseous nerve enters the forearm by passing through the supinator muscle.
It passes beneath a fibrous arch of the supinator known as the Arcade of Frohse, a common site of nerve compression.
After emerging from the supinator:
- It enters the posterior compartment of the forearm.
- Supplies the superficial extensor muscles, followed by the deep extensor muscles of the forearm.
It provides pure motor innervation and has no cutaneous sensory supply.

The superficial branch continues along the lateral aspect of the forearm.
It runs deep to the brachioradialis muscle.
Distally, it becomes subcutaneous and enters the hand.
It provides sensory innervation to:
- The dorsum of the hand
- The dorsal aspects of the radial digits (excluding nail beds)

Injury at the spiral groove may cause:
- Wrist drop
- Loss of finger extension
- Preserved elbow extension if triceps branches are spared
Compression at the Arcade of Frohse may result in:
- Posterior interosseous nerve palsy
- Motor weakness without sensory loss
Injury to the superficial branch leads to:
- Sensory loss over the dorsum of the hand without motor deficit

The spiral groove is the most vulnerable segment of the radial nerve.
Posterior interosseous nerve is purely motor.
Superficial radial nerve is purely sensory.
Understanding the course is essential in trauma, fracture fixation, and surgical approaches around the arm and elbow.

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