Froment’s sign is a classic clinical physical examination maneuver used to evaluate a specific motor deficit in the hand. A positive Froment’s sign (compensatory, extreme interphalangeal joint flexion of the thumb during a forceful key pinch) indicates profound weakness of which muscle and its corresponding nerve?

Explanation:
The correct option is b. The adductor pollicis, innervated solely by the deep branch of the ulnar nerve, is responsible for bringing the thumb firmly against the index finger during a key pinch. When ulnar nerve palsy paralyzes this muscle, the patient cannot maintain a flat, strong pinch. To compensate and hold onto the object (usually a piece of paper), the patient subconsciously recruits the flexor pollicis longus (innervated by the intact anterior interosseous branch of the median nerve), causing the IP joint of the thumb to hyperflex. Reference: Green's Operative Hand Surgery. High-yield orthopaedic mcq.