Describe the radial nerve under the following headings : (i) Origin and course (ii) Branches and muscles supplied (iii) Applied aspects

(i) Origin and Course

The radial nerve originates from the posterior cord of the brachial plexus (C5-T1). Specifically, it’s formed by the contributions from the posterior divisions of the C5, C6, C7, T1, and sometimes C8 spinal nerves.

Its course can be divided into several parts:

• In the Axilla: It initially travels with the profunda brachii artery, passing through the quadrangular space (bordered by teres minor, teres major, long head of triceps, and humerus).
• In the Arm: It runs laterally, deep to the triceps brachii muscle, in the radial groove on the posterior surface of the humerus.
• In the Forearm: At the elbow, it spirals around the lateral epicondyle of the humerus, becoming superficial. Here, it divides into superficial and deep branches.
• Superficial Branch: Runs along the posterior aspect of the forearm.
• Deep Branch: Passes deep to the brachioradialis muscle, continuing into the posterior compartment of the forearm.

The radial nerve’s course makes it vulnerable to injury at several points, particularly around the humerus and elbow.

(ii) Branches and Muscles Supplied

The radial nerve gives off several branches, supplying both motor and sensory innervation.

Motor Branches

• Posterior Cutaneous Nerve of Arm: Supplies skin on the posterior aspect of the arm.
• Posterior Cutaneous Nerve of Forearm: Supplies skin on the posterior aspect of the forearm.
• Branches to Triceps Brachii: Innervates the long and lateral heads of the triceps brachii, responsible for elbow extension.
• Branches to Anconeus: Innervates the anconeus muscle, assisting in elbow extension.
• Deep Branch – Posterior Compartment of Forearm: Supplies the muscles of the posterior compartment of the forearm, including:
  • Supinator: Pronates and supinates the forearm.
  • Abductor Pollicis Longus: Abducts the thumb.
  • Extensor Pollicis Brevis: Extends the thumb.
  • Extensor Pollicis Longus: Extends the thumb.
  • Extensor Indicis: Extends the index finger.
  • Extensor Digitorum: Extends the fingers.
  • Extensor Digiti Minimi: Extends the little finger.
  • Abductor Pollicis Brevis: Abducts the thumb.

Sensory Branches

• Superficial Radial Nerve: Provides cutaneous sensation to the dorsal aspect of the hand, including the thumb, index, middle, and radial half of the ring finger.
• Deep Radial Nerve: Provides proprioceptive sensation to the wrist and fingers.

(iii) Applied Aspects

The radial nerve is susceptible to injury at several locations, leading to distinct clinical presentations:

• Saturday Night Palsy: Compression of the radial nerve against the humerus in the spiral groove, often caused by prolonged pressure (e.g., leaning on elbows). Presents with wrist drop (inability to extend the wrist and fingers) and sensory loss on the dorsal hand.
• Radial Tunnel Syndrome: Compression of the deep branch of the radial nerve as it passes through the radial tunnel (formed by the brachioradialis and extensor carpi radialis longus muscles). Causes pain in the forearm, often mistaken for tennis elbow.
• Fracture of the Humerus: Fractures of the humerus, particularly mid-shaft fractures, can directly injure the radial nerve.
• Humerus Plasty: Surgical procedures involving the humerus can also damage the nerve.

Diagnosis typically involves clinical examination, nerve conduction studies, and electromyography (EMG). Treatment depends on the severity of the injury and may include splinting, physical therapy, or surgical nerve repair.