Video: Flexor pollicis longus muscle

Hey there! It’s Matt from Kenhub, and in this tutorial, we will be discussing the flexor pollicis longus muscle. This muscle is one of the three deep flexors of the forearm lying at the ventral forearm as you see here on this image. The three deep flexors being flexor digitorum profundus, flexor pollicis longus, pronator quadratus. These three deep flexors of the forearm run under the flexor digitorum superficialis, very closely to the radius and ulna and, for that reason, they are difficult to palpate.

The flexor pollicis longus muscle has its origin at the anterior surface of the radius and the interosseus membrane, sometimes also at the medial epicondyle of the humerus. The tendon of flexor pollicis longus runs through the carpal tunnel and inserts at the palmar side of the distal phalanx of the thumb. As almost all flexors of the forearm, this muscle is supplied by the median nerve. The innervating branch is the anterior interosseus nerve.

The deep flexors are mainly responsible for flexion of the hand and finger joints. The flexor pollicis longus is responsible for the flexion of the thumb at the metacarpophalangeal (MCP) and the distal interphalangeal joints (DIP) and opposition at the saddle joint. Furthermore, it bends and radially abducts the hand joint when the thumb is fixed.

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