What is the posterior interosseous nerve and what does it do?

The posterior interosseous nerve is the deep terminal branch of the radial nerve. It is a purely motor nerve that serves as the main nerve supplying most muscles of the posterior forearm compartment.

Where does the posterior interosseous nerve originate and what is its course?

It arises in the cubital fossa at the lateral epicondyle of the humerus. Its course includes passing around the neck of the radius and entering the supinator muscle, emerging from the supinator to run between superficial and deep extensors, and continuing deep to extensor pollicis longus before ending near the wrist.

Which muscles does the posterior interosseous nerve supply?

It supplies all muscles of the posterior forearm except brachioradialis, extensor carpi radialis longus (ECRL), and anconeus. These three muscles are supplied by the radial nerve directly.

What happens if the posterior interosseous nerve is injured?

Injury causes weakness or paralysis of extensors in the posterior forearm. A key clinical feature is that wrist drop is absent because extensor carpi radialis longus remains functional, leading to selective motor deficits rather than complete wrist extension loss.

How is a posterior interosseous nerve injury different from a radial nerve injury?

Posterior interosseous nerve injury spares extensor carpi radialis longus, so wrist drop does not occur. In contrast, a radial nerve injury typically affects this muscle, resulting in the classic wrist drop presentation.

What are the branches of the posterior interosseous nerve?

It has two main types of branches: muscular branches to posterior forearm muscles (timed before, within, and after the supinator) and articular branches supplying the wrist joint, distal radioulnar joint, and carpal joints.

Why is the posterior interosseous nerve important in forearm anatomy?

It is crucial as the primary motor nerve for the posterior forearm compartment. Understanding its course helps explain clinical presentations of nerve injuries and surgical risks during procedures involving the proximal radius.

Posterior Interosseous Nerve – Anatomy & Injury

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