On asking a patient to grip a piece of paper firmly between the thumb and the radial side of the index finger, you observe flexion of the thumb's interphalangeal joint as compensation. Which muscle is weak, and which nerve supplies it?

• A Flexor pollicis brevis, median nerve
• B Adductor pollicis, ulnar nerve ✓
• C First dorsal interosseous, radial nerve
• D Opponens pollicis, recurrent branch of median nerve

Explanation

Froment sign indicates weakness of adductor pollicis, supplied by the deep branch of the ulnar nerve. When thumb adduction fails, the patient substitutes flexor pollicis longus, a median nerve muscle, causing flexion at the interphalangeal joint during key pinch. The test therefore localises an ulnar nerve lesion and is positive in ulnar tunnel syndromes and low ulnar palsies.

Reference: Snell's Clinical Anatomy by Regions, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.