Flexor pollicis longus muscle

Last revised by Dr Henry Knipe on 07 Sep 2022

The flexor pollicis longus (FPL) muscle is one of the two muscles that make up the third layer of the anterior compartment of the forearm along with the flexor digitorum profundus muscle. It is a deep muscle under the abductor pollicis brevis muscle. It passes through the carpal tunnel. It is one of the extrinsic muscles of the hand.

  • origin: mid-anterior surface of the radial shaft and adjacent interosseous membrane
    • frequently the flexor pollicis longus muscle arises from the lower part and slip of coronoid process of ulna by a rounded bundle of muscular fibers and even medial epicondyle of humerus
  • insertion: volar surface of the distal 1st phalanx (thumb)
  • innervation: anterior interosseous nerve
  • action: flexion of 1st interphalangeal joint

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Cases and figures

  • Figure 1: carpal tunnel diagram
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  • Figure 2: carpal tunnel diagram
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