During upper-extremity wound assessment, which nerve is evaluated when the patient abducts the thumb?

• A. Median
• B. Radial
• C. Ulnar
• D. Anterior interosseous

Answer: (A)

Thumb abduction in this context is testing the muscle that moves the thumb away from the palm at the metacarpophalangeal and carpometacarpal joints, the abductor pollicis brevis. That muscle is innervated by the median nerve (via its recurrent branch). So asking the patient to abduct the thumb against resistance is a direct way to assess median nerve motor function in the hand. If this action is weak, it points to a median nerve injury somewhere along its course to the hand. It’s helpful to remember that another muscle, abductor pollicis longus, can also abduct the thumb but is innervated by the radial nerve and is more involved in movements tested by other maneuvers (and extension) rather than a straightforward median-nerve thumb abduction screen. The ulnar nerve governs other thumb and finger movements, such as adduction via the adductor pollicis, which is a different function altogether.