Which nerve mediates thumb abduction and thumb opposition?

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

Answer: (A)

Opposition and many thumb movements hinge on the thenar muscles, especially the muscles that position the thumb across the palm. The nerve that supplies these thenar muscles via its recurrent branch is the median nerve. The opponens pollicis and the flexor pollicis brevis (both key for opposition) and the abductor pollicis brevis (contributes to abduction at the thumb’s base) are innervated by the median nerve, enabling these actions. While the abductor pollicis longus (which also abducts the thumb) is by the radial nerve, the specific combination of opposition and the common thenar abduction comes from the median-innervated muscles. The ulnar nerve mainly handles adductor pollicis and other intrinsic hand muscles, the radial nerve supplies many extensor and some abductor functions not central to opposition, and the musculocutaneous nerve doesn’t innervate hand intrinsic muscles. Clinically, median nerve compromise weakens thumb opposition and weakens thenar-driven abduction, underscoring its role.