Gross Anatomy of the Radial Nerve

Jul 20, 2024

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.