Posterior Interosseous Nerve Syndrome - Finger Drop

Expansion

The posterior interosseous nerve is the deep motor branch of the radial nerve. A lesion causes:

• Finger drop - loss of finger extension at the metacarpophalangeal joints
• Radial deviation of the wrist on extension, because extensor carpi radialis longus is spared but extensor carpi ulnaris is weak
• No sensory loss, as the nerve is purely motor

Common causes include a fracture or dislocation at the elbow and compression at the arcade of Frohse in supinator.