Dr. Ebraheim’s educational animated video describes the anatomy associated with the radial nerve.
The radial nerve receives branches from each nerve root from C5T1. The radial nerve continues into the posterior compartment of the upper arm. The radial nerve then gives three branches in the axialla
1Branch to long head of triceps
2Branch to medial head of triceps
3Posterior cutaneous nerve of the arm
Some books show the position of the posterior cutaneous nerve of the arm being higher than the branches of the triceps. The profunda brachii artery arises from the axiallary artery. The radial nerve next travels through the triangular interval with the profunda brachii artery posteriorly.
Boundaries:
•Teres major
•Long head triceps
•Humeral shaft
Contains the profunda brachii artery and the radial nerve.
The radial nerve enters the upper arm between the long head and the medial head of the triceps and then it runs towards the spiral groove of the humerus.
What is the spiral groove? The spiral groove is a thin, bare area of bone that lies in the upper 2/3 of the back of the humerus. Between the lateral and medial head of triceps. There are posterior safe zones of the humerus, 10 cm distal to the lateral acromion and 10 cm proximal to the lateral epicondyle. Four branches arise from the radial nerve within the spiral groove:
1Branch to lateral head of triceps
2Branch to medial head of triceps
3Lower lateral cutaneous nerve of the arm
4Posterior cutaneous nerve of the forearm
In the posterior approach, if the surgeon follows these cutaneous nerves proximally, it will lead to the identification of the radial nerve itself.
The radial nerve passes through the lateral intermuscular septum, running between the brachialis and brachioradialis muscle anterior to the lateral epicondyle (site for surgical exposure).
Anterior view: the radial nerve gives branches to supply the lateral part of the brachialis, brachioradialis, extensor carpi radials longus, and the extensor carpi radialis brevis muscle.
The radial nerve is vulnerable to injury below the spiral groove when there is fracture in the distal third of the humeral shaft. Injury to the nerve will cause the condition of wrist drop. At about the level of the lateral epicondyle, the radial nerve begins to divide into deep branch and the superficial branch of the radial nerve. The posterior interosseous nerve (Deep) enters the extensor compartment of the forearm through the supinator muscle. The area in which the posterior interosseous nerve passes through is called “Arcade of Frohse” and this area is often a site of entrapment of the nerve. The posterior interosseous supplies these muscles on the radial side and dorsal surface of the forearm:
1Extensor carpi ulnaris
2Extensor digiti minimi
3Extensor digitorium
4Extensor pollicis brevis
5Extensor indices
6Extensor pollicis longus
7Abductor pollicis longus
The posterior interosseous nerve does not supply cutaneous sensation and is purely motor.
The superficial radial nerve runs deep to the brachioradialis muscle. The superficial radial nerve continues until about 5 cm above the wrist where it immerges from underneath the brachioradialis muscle, piercing the deep fascia and descending towards the anatomical snuff box. The superficial radial nerve is a sensory nerve supplying the majority of the dorsum of the hand. The sensory areas involving the cutaneous branches of the upper arm and forearm and the superficial sensory radial nerve are shown here.

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audio is provided as a free download