AIN Motor Branch Median Nerve — FRCA Primary MCQ
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Correct answer: B — Median nerve
The anterior interosseous nerve (AIN) branches from the median nerve in the proximal forearm. It is a purely motor nerve (no cutaneous sensory component) supplying: flexor pollicis longus / flexor digitorum profundus (index and middle fingers) / and pronator quadratus. AIN palsy causes inability to make an 'OK' sign (pinch between thumb and index finger).
Reference: RCoA 2021 Primary FRCA Curriculum