The 'Froment's sign' is positive in ulnar nerve palsy. It tests for weakness of which specific muscle and which action?

• A Opponens pollicis — opposition of the thumb
• B Adductor pollicis — adduction of the thumb against resistance ✓
• C Flexor pollicis brevis — flexion of the proximal phalanx of thumb
• D Abductor pollicis brevis — abduction of the thumb

Explanation

Froment's sign tests the adductor pollicis (innervated by the deep branch of ulnar nerve). When a patient is asked to hold a piece of paper between the thumb and index finger, ulnar nerve palsy causes inability to adduct the thumb using adductor pollicis. To compensate, the patient flexes the interphalangeal joint of the thumb using flexor pollicis longus (median nerve) — this compensatory flexion constitutes a positive Froment's sign. Jeanne's sign (hyperextension of thumb MCP during pinch) may accompany it. The test specifically identifies adductor pollicis weakness.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.