Flexor Pollicis Longus

Joe Muscolino

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Flexor pollicis longus is seen. The pronator quadratus and brachialis have been ghosted in.

The Flexor Pollicis Longus is in the Deep Layer of the Anterior Forearm Compartment.

The Flexor Pollicis Longus has two heads: Radial Head and Humeroulnar Head.



  • Anterior radius to the thumb
    • The humeroulnar head attaches onto the medial epicondyle of the humerus and the coronoid process of the ulna.
    • The distal tendon attaches onto the anterior surface of the distal phalanx.



  • Flexes the thumb at the carpometacarpal, metacarpophalangeal, and proximal and distal interphalangeal joints.
  • Flexes the hand at the wrist joint.
  • Flexes the forearm at the elbow joint.
  • Pronates the forearm at the radioulnar joints.



  1. The distal tendon of the flexor pollicis longus runs through the carpal tunnel and can be involved with carpal tunnel syndrome.
  2. The humeroulnar head is often extremely small or missing entirely.