Gross Anatomy of the Radial Nerve

Overview

• Chief nerve of the upper limb along with ulnar and median nerves.
• Innervates almost all muscles of the posterior compartment of the arm and forearm.
• Called the nerve of the posterior compartment of the arm and forearm.

Location in the Axilla

• Located in relation to the third part of the axillary artery.
• Associated with the axillary nerve, originating from the posterior cord of the brachial plexus.

Course and Branches

Origin

• From the posterior cord of the brachial plexus.
• Located behind the third part of the axillary artery.

Descent

• Passes from anterior to posterior via the triangular interval bounded by teres major, long head of the triceps, and later head of the triceps.
• Spirals around the mid-shaft of the humerus in the spiral groove.

Structure Relationship

• Radial nerve and profunda brachii artery run together in the spiral groove.
• Supplies lateral, medial, and long head of the triceps.

Branches Before Elbow

• Branch to brachioradialis muscle.
• Branch to anconeus muscle.
• Branch to extensor carpi radialis longus.

At Elbow (Cubital Fossa)

• Divides into deep and superficial branches.

Deep Branch

Path

• Passes into the supinator muscle via the radial tunnel (Arcade of Frohse).
• Becomes the posterior interosseous nerve after passing through the radial tunnel.

Innervation

• Supinator muscle (by deep branch, not posterior interosseous nerve).
• Supplies all wrist extensors (extensor carpi radialis brevis, extensor carpi ulnaris, extensor digitorum, extensor indicis, extensor digiti minimi).
• Long-term muscles: extensor pollicis longus, extensor pollicis brevis, abductor pollicis longus.

End

• Ends as a pseudo ganglion providing sensory innervation to the dorsal wrist capsule.

Superficial Branch

Sensory Innervation

• Arm: Inferior lateral cutaneous nerve, posterior cutaneous nerve.
• Forearm: Posterior cutaneous nerve of the forearm.
• Hand: Thenar eminence, dorsal aspect of the radial three digits.

Applied Anatomy

General Vulnerability

• Prone to injury along its entire course from origin to termination.

Injuries at Axilla

• Saturday Night Palsy/Crutch Palsy/Honeymoon Palsy: Compressive neuropathy in the axilla leading to wrist drop.
• Symptoms: Inability to extend the wrist (wrist drop), decreased grip strength.

Injuries at Arm

• Common in mid-shaft humeral fractures due to proximity to the spiral groove.
• Symptoms: Wrist drop, inability to extend elbow, diminished sensation in posterior arm and forearm.

Injuries at Elbow

• Radial Tunnel Syndrome: Chronic compression within the radial tunnel causing lateral elbow pain without weakness or sensory deficits.
• Posterior Interosseous Nerve Syndrome: Weakness of extensor muscles due to fractures or chronic soft tissue compression.

Injuries at Wrist

• Wartenberg Syndrome: Compression of the superficial branch, leading to sensory loss on the dorsal aspect of the radial three digits, no motor deficits.

Key Points

• Proximal lesions involve more extensor muscles, leading to greater degree of wrist drop.

Conclusion

• Detailed understanding of the origin, course, branches, and clinical anatomy of the radial nerve.
• Important for recognizing and diagnosing different types of radial nerve injuries.