Question

A median nerve lesion at the wrist causes all of the following, except:

• A. Thenar atrophy
• B. Weakness of adductor pollicis
• C. Weakness of 1st and 2nd lumbricals
• D. Weakness of flexor pollicis brevis

Hint:

Adductor pollicis is ulnar, not median; remember the LOAF muscles for the median nerve.

Answer 1

The Correct Option is B

Step 1: List what the median nerve supplies in the hand. At and below the wrist, the median nerve (through its recurrent branch and digital branches) supplies the thenar muscles, abductor pollicis brevis, opponens pollicis and flexor pollicis brevis, plus the first and second lumbricals. A memory aid is LOAF: Lumbricals 1 and 2, Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis.

Step 2: Map the true effects. A lesion at the wrist denervates the thenar muscles, so the thenar eminence wastes (thenar atrophy, option A is true). It weakens flexor pollicis brevis (option D is true) and weakens the first and second lumbricals (option C is true).

Step 3: Identify the muscle that is NOT median supplied. Adductor pollicis is supplied by the deep branch of the ulnar nerve, not the median nerve.

Step 4: Conclude. A median nerve lesion at the wrist would not weaken adductor pollicis, because that muscle keeps its ulnar nerve supply. This is also why Froment sign (testing adductor pollicis) is positive in ulnar palsy, not median palsy.

Step 5: The exception in this question is Weakness of adductor pollicis (option B).