Surgical Anatomy• Deep to the lateral head of the triceps, piercing the intermuscular septum; lie between the brachialis and brachioradialis.• Motor branches to the brachioradialis, extensor carpi radialis longus, and to the lateral part of the brachialis muscle.
At the level of the lateral epicondyle the radial nerve dividesinto superficial and deep branches.Motor branch to supinator.
Summary• PIN arises from radial nerve. Radial nerve pulak arises from posterior cord of the brachial plexus• It passes posterior to the axillary artery between long and media heads of triceps muscle, to lie in the spiral groove between medial & lateral heads of triceps muscle.• Here it is accompanied by the profunda brachii artery before it pierces it lateral intermuscular septum of the lower third humerus to run between brachialis & brachioradialis• At the lateral of epicondyle humerus, it gives rises to PIN & superficial radial nerve
• Radial nerve supply all the extensor muscle of forearm & arm. However it also supply brachioradialis, which is flexor of elbow when forearm pronated• Damage to the nerve in the spiral groove causes wrist drop but no loss of elbow extension, as fibres of triceps remain intact proximal to this site• Only damage in the axilla will causes loss of elbow extension & wrist drop• Damage to posterior interosseus nerve (PIN) does not cause wrist drop because extensor carpi radialis longus receives its innervation from the main radial nerve• Pin only cause unable to extend metacarpophalangeal joint finger drop.