Quick Facts
Origin: Anterior surface of radius and adjacent interosseous membrane of forearm.
Insertion: Palmar aspect of base of distal phalanx of thumb.
Action: Flexes thumb.
Innervation: Anterior antebrachial interosseous nerve (C7-T1).
Arterial Supply: Anterior interosseous and radial arteries.
Related parts of the anatomy
Origin
The flexor pollicis longus muscle originates from the:
- anterior surface of the radius, which is located inferior to the insertion site of the supinator muscle and superior to the insertion site of the pronator quadratus muscle;
- adjacent interosseous membrane of forearm.
It may also originate from the coronoid process of ulna or the medial epicondyle of the humerus.
Insertion
The fibers of the flexor pollicis longus muscle travel inferiorly to the hand and insert, via a flat tendon, onto the palmar aspect of the base of the distal phalanx of thumb.
Key Features & Anatomical Relations
The flexor pollicis longus muscle is one of the muscles of the deep part of the anterior compartment of the forearm. It is a unipennate type of skeletal muscle. At the wrist, its tendon travels deep to the flexor retinaculum of hand, where it passes through the tendinous sheath of flexor pollicis longus. Within the palm of the hand, the tendon travels between the opponens pollicis muscle and the oblique head of adductor pollicis muscle. The tendon travels between the sesamoid bones of hand, passes through the fibrous sheath that is found along the palmar aspect of thumb to its insertion site.
The flexor pollicis longus muscle is located:
- anterior (superficial) to the radius, the interosseous membrane of forearm, and the pronator quadratus muscle;
- posterior (deep) to the flexor digitorum superficialis and brachioradialis muscles;
- medial to the extensor carpi radialis longus muscle and the radial artery;
- lateral to the flexor digitorum profundus muscle and the anterior antebrachial interosseous nerve.
Actions & Testing
The flexor pollicis longus muscle is involved in multiple actions:
- flexes the distal phalanx at the interphalangeal joint of the thumb;
- assists in flexion of the proximal phalanx at the metacarpophalangeal joint of the thumb;
- assists in flexion of the first metacarpal bone (of thumb) at the first carpometacarpal joint;
- assists in flexion of the hand at the radiocarpal (wrist) joint.
The flexor pollicis longus muscle can be tested by flexing the distal phalanx of thumb at its interphalangeal joint against resistance, while its proximal phalanx is held in position (Sinnatamby, 2011).
References
Sinnatamby, C. S. (2011) Last's Anatomy: Regional and Applied. ClinicalKey 2012: Churchill Livingstone/Elsevier.
