The posterior interosseous nerve is the deep, predominantly motor branch of the radial nerve after it divides at the lateral elbow. It supplies all the forearm extensors except the extensor carpi radialis longus (which receives a direct radial nerve branch above the division). Its passage through the supinator muscle between the superficial and deep heads creates the radial tunnel where compression produces posterior interosseous nerve syndrome.
| Origin | Deep branch of the radial nerve, arising at the level of the lateral epicondyle |
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Posterior interosseous nerve syndrome produces weakness of finger and wrist extension without sensory loss, because the nerve has no cutaneous territory. This distinguishes it from a more proximal radial nerve palsy that includes sensory loss. Compression can be from a mass lesion such as a lipoma, radial head fracture, rheumatoid synovitis at the radial head, or repetitive forearm rotation. The radial tunnel syndrome is a related pain syndrome without motor deficit, thought to reflect irritation rather than compression.
Motor compression producing finger and wrist extensor weakness without sensory loss, caused by radial tunnel masses, radial head fractures, or supinator hypertrophy, managed with decompression if a structural cause is identified.
