Which sign is positive in ulnar nerve impairment at the hand?

• A. Froment's sign
• B. Tinel's sign
• C. Phalen's sign
• D. Finkelstein's sign

Answer: (A)

In ulnar nerve impairment at the hand, the intrinsic hand muscles that control thumb adduction, especially the adductor pollicis, lose function. When you try to pinch a piece of paper between the thumb and index finger, that weakened adductor pollicis can’t hold the thumb in place. The person then relies on the flexor pollicis longus (driven by the median nerve) to flex the thumb’s interphalangeal joint to maintain the grip. That compensatory flexion of the thumb’s IP joint during pinching is Froment’s sign, and its presence points to ulnar nerve dysfunction at the hand.

The other signs are not specific to this situation: Tinel’s sign is about nerve irritation along a path and can be positive in various entrapments; Phalen’s sign tests median nerve compression at the carpal tunnel; Finkelstein’s sign checks for De Quervain’s tenosynovitis.