|Origin||Anterior surface radius|
Adjacent interosseous membrane of forearm
|Insertion||Palmar aspect of base of distal phalanx of thumb|
Very weakly assists in flexing the wrist
|Nerve||Anterior interosseous nerve (C7, C8)|
|Artery||Anterior interosseous artery|
Location & Overview
The flexor pollicis longus muscle is located in the anterior part of the forearm and is one of the three deep flexor muscles found in the volar compartment of the forearm. The other two muscles in this compartment are the flexor digitorum profundus and pronator quadratus muscles. This muscle lies deep to the radial head of the flexor digitorum superficialis muscle and is distal to the supinator muscle. Its primary function is to flex the thumb, making it a key muscle for grip strength. Despite being located in the forearm, the flexor pollicis longus is classified as one of the extrinsic muscles of the hand   .
In Latin, ‘pollicis’ means ‘of the thumb’, ‘flexor’ means ‘a muscle that flexes a joint’, and ‘longus’ means ‘long’. So translated into English, flexor pollicis longus is ‘long flexor muscle of the thumb’. Studies have shown that the flexor pollicis longus is only present in approximately 48% of the population .
Origin & Insertion
The flexor pollicis longus originates on the anterior surface of the radius (also know as the volar aspect), just distal to the radial tuberosity. It also originates from the adjacent interosseous membrane. The interosseous membrane is a strong fibrous sheet that connects the radius and ulna bones, which run parallel to each other in the forearm. The flexor pollicis longus also passes deep to the flexor retinaculum, also known as the transverse carpal ligament. The muscle then proceeds towards its insertion on the palmar aspect of the base of the distal phalanx of the thumb   .
The flexor pollicis longus muscle is the primary flexor of the thumb. It provides flexion at both the metacarpophalangeal and interphalangeal joints. In addition to thumb flexion, it can support other muscles by contributing weak flexion of the wrist joint  .
The flexor pollicis longus is innervated by the anterior interosseous nerve. The anterior interosseous nerve is a branch of the median nerve and passes in between the two heads of the pronator teres muscle  .
Blood is supplied to the flexor pollicis longus from the anterior interosseous artery. The anterior interosseous artery is a branch of the ulnar artery. Branches of the median nerve artery also provide blood to the flexor pollicis longus’ pre-digital portion. The digital portion of the tendon gets its blood supply from vincula: V1 and V2. V1 originates from either the princeps pollicis artery or both digital arteries. V2 originates from both digital arteries  .
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Flexor Pollicis Longus Flashcards
|↑1, ↑5, ↑8, ↑10, ↑12||Moore KL, Agur AMR, Dalley AF. Clinically Oriented Anatomy. 8th ed. Philadelphia: Lippincot Williams & Wilkins; 2017|
|↑2, ↑6, ↑9, ↑11, ↑13||Benson DC, Miao KH, Varacallo M. Anatomy, Shoulder and Upper Limb, Hand Flexor Pollicis Longus Muscle. [Updated 2021 Jul 26]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK538490/|
|↑3, ↑7||Standring S. (2015). Gray’s Anatomy: The Anatomical Basis of Clinical Practice, 41st Edn. Amsterdam: Elsevier.|
|↑4||Asghar, A., Jha, R. K., Patra, A., Chaudhary, B., & Singh, B. (2022). The prevalence and distribution of the variants of Gantzer’s muscle: a meta-analysis of cadaveric studies. Anat Cell Biol, 55(1), 3-13. https://doi.org/10.5115/acb.21.141|