Radial Nerve Lesion

Question 1

The Path

Answer 1

Continuation of the posterior cord of the brachial plexus (C5-T1)

Goes below the clavicle to the posterior axillary wall

Between the long and medial heads of triceps

It then continues to the spiral groove of the humerus, deep to the lateral head of triceps
It winds around the humerus to the lateral side where it travels to the anterior arm (superficial)

Travels between the brachialis and brachioradialis, passing the extensor carpi radialis longus and extensor carpi radialis brevis

The nerve crosses the elbow joint to the supinator

The radial nerve then divides into:

• The posterior motor branch which enters the supinator muscle, then travels down the lateral aspect of the radius, innervating extensor digitorum, extensor carpi ulnaris, extensor pollicis longus and brevis, abductor pollicis longus, extensor indicis and extensor digiti minimi and terminates at the wrist
• The superficial branch continues down the arm under the brachioradialis, crossing supinator, and travels with the radial artery. It continues on the dorsal surface of the arm, becoming superficial to abductor pollicis longus and extensor pollicis brevis. It divides into more branches after crossing the extensor retinaculum and innervates the dorsal surface of the hand, lateral to a line midway through the fourth digit

Question 2

Muscles Innervated by the Radial Nerve

Answer 2

Triceps
Anconeus
Brachioradialis
Extensor carpi radialis longus
Extensor carpi radialis brevis
Supinator
Extensor digitorum
Extensor carpi ulnaris
Extensor digiti minimi
Extensor pollicis longus
Extensor pollicis brevis
Abductor pollicis longus
Extensor indicis

Question 3

Causes of Lesions of the Radial Nerve

Answer 3

• Fractures:

Primarily at the spiral radial groove and at the supracondylar and upper ⅓ of the radius

• Dislocations;

Of the head of the radius, humeroradial and radioulnar joints

• Post-surgical complications:

Due to unrelieved pressure on the lateral arm from poor positioning during surgery

• Compression:

Primarily at the axilla from crutch use. A condition known as “Saturday night palsy” occurs when the arm is draped over the back of a chair or table edge or when the arm is fully abducted and supporting the head against a hard surface

• Supinator syndrome:

Compressions can occur in the forearm. Fibrosis, usually due to overuse, at the site where the nerve penetrates the supinator muscle leads to the syndrome

Question 4

Symptom Picture

Answer 4

Presentation of a complete radial nerve lesion is known as a wrist drop

The hand hangs in flexion because the wrist flexors are unopposed due to the flaccid wrist extensors

When the injury is proximal to the elbow, before the radial nerve branches, both sensory and motor function are affected. When the injury is distal to the elbow, often only one branch is affected, either motor or sensory

Muscle wasting is possible depending on the lesion site

There may be swelling on the dorsum of the hand

Question 5

Sensory Dysfunction as a Result of a Lesion

Answer 5

Altered sensation is experienced at the posterior arm, forearm and hand, specifically in the thumb, index, middle and ½ of the ring finger, excluding the fingertips

Anesthesia (area of isolated supply) occurs at the web between the thumb and second digit