Radial

Question 1

The radial nerve is a

Answer 1

major peripheral nerve of the upper limb.

Question 2

Nerve roots:

Answer 2

C5-T1.

Question 3

Motor

Answer 3

Innervates the triceps brachii, responsible for extension at the elbow. Innervates the majority of the extensor muscles in the forearm, responsible for extension of wrist and fingers and supination of the forearm

Question 4

Sensory:

Answer 4

Innervates most of the skin of the posterior side of forearm, and the dorsal surface of the lateral side of the palm, and lateral three and a half digits.

Question 5

Anatomical Course

Answer 5

The radial nerve is a continuation of the posterior cord of the brachial plexus, containing nerve fibres from all 5 roots (C5 – T1).
The nerve arises in the axilla, exiting posteriorly to the brachial artery. Here it supplies branches to the long and medial heads of the triceps brachii. The radial nerve then descends down the arm, travelling in a shallow depression on the surface of the humerus. This depression is known as the radial groove.

As it moves inferiorly, the radial nerve wraps around the humerus in a lateral direction, and gives a branch to the lateral head of the triceps brachii. During its course in the arm, the nerve is accompanied by the deep branch of the brachial artery.

To enter the forearm, the radial nerve moves anteriorly over the lateral epicondyle of the humerus, through the cubital fossa. Within the forearm, the nerve terminates by dividing into two branches:

Deep branch – A motor branch. It innervates the muscles in the posterior compartment of the forearm.
Superficial branch – A sensory branch. It contributes to the cutaneous innervation of the hand and fingers.

Question 6

Sensory Functions

Answer 6

There are four branches of the radial nerve that provide cutaneous innervation to the skin of the upper limb:

Lower lateral cutaneous nerve of arm – Innervates the lateral aspect of the upper arm, below the deltoid muscle.
Posterior cutaneous nerve of arm – Innervates the posterior surface of the upper arm.
Posterior cutaneous nerve of forearm – Innervates a strip of skin down the middle of the posterior forearm.
Superficial branch of the radial nerve – Innervates the dorsal surface of the lateral three and half digits, and their associated palm area.

Question 7

Motor Functions

Answer 7

The radial nerve innervates muscles located in the arm and forearm.

In the arm, it directly innervates the three heads of the triceps brachii. This muscle performs extension at the elbow. In the forearm, the deep branch of the radial nerve innervates the muscles in the posterior compartment of the forearm. These muscles generally extend at the wrist and finger joints.

Question 8

Clinical significance

Answer 8

At the axilla

Common mechanisms of injury: Saturday night palsy, crutch palsy
Motor deficit:
Loss of extension of forearm, weakness of supination, and loss of extension of hand and fingers.
Presence of wrist drop, due to inability to extend the hand and fingers.
Sensory deficit: Loss of sensation in lateral arm, posterior forearm, the radial half of dorsum of hand, and dorsal aspect of radial 3 1⁄2 digits, excluding their nail beds.
At mid-arm

Common mechanism of injury: Mid-shaft humeral fracture
Motor deficit:
Weakness of supination, and loss of extension of hand and fingers.
Presence of wrist drop, due to inability to extend the hand and fingers.
Sensory deficit: Loss of sensation in posterior forearm, the radial half of dorsum of hand, and dorsal aspect of radial 3 1⁄2 digits, excluding their nail beds.
Just below the elbow

Common mechanism of injury: Neck of radius fracture, elbow dislocation or fracture, tight cast, rheumatoid nodules, injections due to tennis elbow, injuring the deep branch of the radial nerve that pierces the radial head, causing posterior interosseous nerve syndrome
Motor deficit:
Weakness in extension of hand and loss of extension of fingers.
Presence of finger drop, and partial wrist drop, since the extensor carpi radialis longus and brachioradialis muscles are working.
Sensory deficit: None, as sensation is supplied by the superficial radial nerve
Within the distal forearm:

Common mechanism of injury: Wartenberg’s syndrome, (not to be confused with Wartenberg’s sign), due to nerve entrapment beneath the tendinous insertion of brachioradialis, tight jewellery, and watch bands.
Motor deficit: None
Sensory deficit: Numbness and tingling in radial half of dorsum of hand, and dorsal aspect of radial 3 1⁄2 digits, excluding their nail beds.
In Wartenberg’s syndrome, there is significant radial wrist pain, and close resemblance to symptoms in de Quervain’s tenosynovitis. Finkelstein’s test may be positive.