Ape hand deformity and Benediction sign both indicate injury to the same nerve. Which nerve is it?

• A. Ulnar nerve
• B. Radial nerve
• C. Median nerve
• D. Axillary nerve

Answer: (C)

Both ape hand deformity and Benediction sign come from loss of median nerve function, which disrupts thumb opposition and the flexion of the index and middle fingers. When the median nerve is injured, the thenar muscles that allow the thumb to oppose (opponens pollicis and flexor pollicis brevis) are paralyzed, so the thumb cannot rotate toward the palm and the hand adopts an “ape” appearance with the thumb held in an adducted position.

At the same time, flexing the index and middle fingers relies on the lateral portion of the flexor digitorum profundus and the flexor digitorum superficialis, both of which are supplied by the median nerve. If the nerve is injured proximally, these muscles can’t flex those digits, so when a fist is attempted, the index and middle fingers stay extended while the ring and little fingers (innervated by the ulnar nerve) can still flex. This combination—loss of thumb opposition and inability to flex the index and middle fingers—points to injury of the median nerve rather than the radial, ulnar, or axillary nerves.