Flexor pollicis longus

Dr Bahman Rasuli and Dr Henry Knipe et al.

Flexor pollicis longus (FPL) 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. It is a deep muscle under 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 FPL 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

Variant anatomy

Anatomy: Upper limb

Anatomy: Upper limb

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Article information

rID: 23266
Section: Anatomy
Synonyms or Alternate Spellings:
  • FPL
  • Flexor pollicis longus muscle

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Cases and figures

  • Figure 1: carpal tunnel diagram
    Drag here to reorder.
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