Which nerve is most likely affected in thenar atrophy?

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

Answer: (B)

The muscles of the thenar eminence (the thumb’s thenar group) are innervated mainly by the recurrent branch of the median nerve. When this motor input is lost, the thenar muscles—responsible for thumb opposition, abduction, and flexion—waste away, leading to thenar atrophy. The other nerves don’t primarily supply these muscles: the ulnar nerve mainly innervates the adductor pollicis (and most intrinsic hand muscles like interossei and the hypothenar group), so its injury produces a different pattern of hand weakness; the radial nerve affects mainly the extensor compartments, causing issues like wrist drop; and the axillary nerve innervates the deltoid and teres minor, not the hand muscles. Thus, median nerve involvement best explains thenar atrophy.