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A 50-year-old woman who works as a secretary comes to the physician because of numbness and tingling in her hands. On examination, the patient is found to have decreased sensation in all of her fingers except her fifth digit. Which of the following muscles is most commonly weakened in patients with this condition?

(A) Adductor pollicis
(B) Dorsal interossei
(C) Lumbricals (3 and 4)
(D) Opponens digiti minimi
(E) Opponens pollicis
in Anatomy by

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The correct answer is E. This woman has car- pal tunnel syndrome, which occurs in individuals whose work involves repetitive hand motions. The median nerve is compressed in the carpal tunnel, leading to decreased sensation on the first three and one-half digits and loss of strength of the thumb due to weakness of the abductor pollicis brevis and opponens pollicis. The opponens pollicis is supplied by the me- dian nerve and functions to aid in opposition.

Answer A is incorrect. The adductor pollicis is innervated by a branch of the ulnar nerve and thus would not be affected by carpal tunnel syndrome. It functions to adduct the thumb to- ward the middle digits.

Answer B is incorrect. Dorsal interossei muscles are innervated by a branch of the ulnar nerve, which functions to abduct the digits.

Answer C is incorrect. The third and fourth lumbricals are innervated by a branch of the ulnar nerve.

Answer D is incorrect. The opponens digiti minimi muscle is innervated by a branch of the ulnar nerve and brings the fifth digit in opposition with the thumb.