Introduction: the radial nerve is the direct continuation of the posterior cord of the brachial plexus. It is the largest branch of the brachial plexus.
Arm: the radial nerve enters the arm posterior to the branchial artery, medial to the humerus and anterior to the long head of the triceps muscle. It passes inferiolaterally with the profunda brachii Artery in the radial groove. It then Pierces the lateral intermuscular septum and continues inferiorly between the brachialis and brachioradialis muscles.
Above the wrist it emerges from beneath the brachioradialis to end by dividing into cutaneous nerves to the posterior aspect of the radial 3½ digits.
Muscular: – posterior interosseous nerve to the extensor muscles.
                   – deep branch of the radial nerve
Cutaneous: – posticutaneous nerve of arm
                    – lower lateral cutaneous nerve of arm
                    – posterior cutaneous nerve of forearm.
Clinical correlates:
1. Injury of the radial nerve in the axilla by a crutch causes crutch palsy or may be compressed when a drunkard falls into an intoxicated sleep with the arm hanging over the back of the chair
2. Damage to the main trunk of the radial nerve results in wrist drop due to paralysis of all the wrist extensors.