Flexor Pollicis Longus Muscle Anatomy

Overview
Origin Anterior surface radius
Adjacent interosseous membrane of forearm
Insertion Palmar aspect of base of distal phalanx of thumb
Action Flexes 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 of the forearm and is one of three deep flexor muscles in the forearm’s volar compartment (the other two are the flexor digitorum profundus and pronator quadratus). It is deep to the radial head of the flexor digitorum superficialis muscle and distal to the supinator muscle. The flexor pollicis longus is the primary flexor of the thumb [1]Moore KL, Agur AMR, Dalley AF. Clinically Oriented Anatomy. 8th ed. Philadelphia: Lippincot Williams & Wilkins; 2017 [2]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; … Continue reading [3]Standring S. (2015). Gray’s Anatomy: The Anatomical Basis of Clinical Practice, 41st Edn. Amsterdam: Elsevier..

Origin & Insertion

The flexor pollicis longus originates on the anterior surface of the radius (volar aspect) and the adjacent interosseous membrane. This origin point is just distal to the radial tuberosity. It also passes deep to the flexor retinaculum (transverse carpal ligament) [4]Moore KL, Agur AMR, Dalley AF. Clinically Oriented Anatomy. 8th ed. Philadelphia: Lippincot Williams & Wilkins; 2017 [5]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; … Continue reading [6]Standring S. (2015). Gray’s Anatomy: The Anatomical Basis of Clinical Practice, 41st Edn. Amsterdam: Elsevier..

Actions

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 provide very weak wrist flexion and radial wrist deviation [7]Moore KL, Agur AMR, Dalley AF. Clinically Oriented Anatomy. 8th ed. Philadelphia: Lippincot Williams & Wilkins; 2017 [8]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; … Continue reading.

Innervation

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 [9]Moore KL, Agur AMR, Dalley AF. Clinically Oriented Anatomy. 8th ed. Philadelphia: Lippincot Williams & Wilkins; 2017 [10]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; … Continue reading.

Blood Supply

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 [11]Moore KL, Agur AMR, Dalley AF. Clinically Oriented Anatomy. 8th ed. Philadelphia: Lippincot Williams & Wilkins; 2017 [12]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; … Continue reading.

Images

Here we can see the flexor pollicis longus muscle. We can see a superficial view with the flexor pollicis longus highlighted in green and an isolated view of the muscle by itself.

Here we can see the first origin point of the flexor pollicis longus highlighted in red. The origin is on the anterior surface of the radius.

Here we can see the second origin point of the flexor pollicis longus on the interosseous membrane of forearm.

Here we can see the insertion of the flexor pollicis longus highlighted in blue. The insertion is on the palmar aspect of the base of the distal phalanx of the thumb.

Here we can see the different bones and joints in the thumb colour coded to their respective location.

Want some flashcards to help you remember this information? Then click the link below:
Flexor Pollicis Longus Flashcards

References

References
1, 4, 7, 9, 11 Moore KL, Agur AMR, Dalley AF. Clinically Oriented Anatomy. 8th ed. Philadelphia: Lippincot Williams & Wilkins; 2017
2, 5, 8, 10, 12 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, 6 Standring S. (2015). Gray’s Anatomy: The Anatomical Basis of Clinical Practice, 41st Edn. Amsterdam: Elsevier.