A patient with suspected intrinsic hand muscle weakness is asked to grip a sheet of paper between the thumb and the radial side of the index finger. As the examiner pulls the paper away, the tip of the thumb bends sharply at its interphalangeal joint. This positive Froment's sign indicates weakness of which muscle?

• A Flexor pollicis longus
• B Abductor pollicis brevis
• C First dorsal interosseous
• D Adductor pollicis ✓

Explanation

Froment's sign tests adductor pollicis, an ulnar nerve muscle that holds the paper by thumb adduction. When it is weak, flexor pollicis longus, a median nerve muscle, substitutes by flexing the thumb at the interphalangeal joint to keep hold of the paper. The visible IP joint flexion is therefore the compensation of the intact median nerve, which is exactly what distinguishes the key from options A and B.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.