During pinch assessment, which sign indicates ulnar nerve involvement when pinching?

• A. Wartenberg's sign
• B. Froment's sign
• C. Jeanne's sign
• D. Ulnar claw

Answer: (B)

The key idea here is that a precise pinch relies on the thumb being able to adduct, a function powered by the adductor pollicis which is controlled by the ulnar nerve. When the ulnar nerve is injured, adductor pollicis weakness forces the person to compensate by using the flexor pollicis longus (which is median-nerve–innervated) to grip. This compensation pulls the thumb’s distal joint into flexion during a pinch, so the pinch test reveals the sign where the tip of the thumb flexes rather than cleanly meeting the index finger. That is Froment’s sign, the classic indicator of ulnar nerve involvement in pinch assessment.

Other signs can appear with ulnar nerve problems, like the little finger drifting outward (Wartenberg sign) or overall hand deformities such as clawing, but the specific cue during pinching—the flexed thumb tip indicating loss of adductor pollicis—points to Froment’s sign.