Causes / typical injury mechanism: In general, posterior interosseus nerve (PIN) compression syndrome is caused by either trauma, inflammation, or space-occupying lesions. Traumatic causes include –

• Microtrauma from repetitive pronosupination
• Fractures and dislocations: radial head, Monteggia

Space-filling lesions include mainly lipomas and ganglions.

Inflammatory causes primarily involve rheumatoid synovitis of the radiocapitellar joint.

Iatrogenic causes following surgical intervention are also described.

Classic history and presentation: Classically, a young male laborer or bodybuilder doing repetitive pronosupination activities presenting with forearm and wrist pain, weakness of thumb and wrist extensors, and no sensory deficits.

Prevalence: 2-4 per 100 000 people per year in the United States.

• Age – most common in the second to fourth decade of life
• Sex / gender – more common in males

Risk factors:

• Repetitive pronosupination activities
• Compressive lesions
• Elbow trauma (ie, Monteggia fracture or radial head fracture)
• Rheumatoid arthritis

Pathophysiology: PIN compression syndrome is caused by compression of the posterior interosseous nerve at either the leash of Henry, extensor carpi radialis brevis (ECRB) edge, arcade of Frohse, supinator muscle edge, or fibrous tissue between the brachialis and brachioradialis. Compression causes muscle weakness of the wrist and finger extensors without sensory changes.