Musculoskeletal anatomy · USMLE Step 1

A patient with carpal tunnel syndrome experiences weakness in thumb flexion. Which muscle is likely affected?

  1. Flexor pollicis longus (flexes thumb IP joint)
  2. Flexor pollicis brevis (superficial head)
  3. Adductor pollicis (thumb adduction)
  4. Abductor pollicis longus (thumb abduction)
Show answer and explanation

Correct answer: Flexor pollicis brevis (superficial head)

The superficial head of flexor pollicis brevis is innervated by the median nerve, which is compressed in carpal tunnel syndrome. This results in weakened thumb flexion.

Difficulty: Medium Question 20 of 20

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