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The flexor pollicis longus (FPL) is a long muscle in the forearm and hand that flexes the thumb. It is one of the three deep flexors of the volar compartment of the forearm, and the only muscle that flexes the interphalangeal joint of the thumb, making it essential for gripping. The FPL muscle is innervated by the median nerve and receives dual blood supply from the anterior interosseous artery (a branch of the ulnar artery) and the radial artery.
| Characteristics | Values |
|---|---|
| Full Form | Flexor Pollicis Longus |
| Muscle Type | Long muscle located in the forearm and hand |
| Function | Flexes the thumb at the interphalangeal joint, flexion of the wrist |
| Blood Supply | Anterior interosseous artery, a branch of the ulnar artery |
| Innervation | Median nerve (anterior interosseous branch) |
| Occurrence in Humans | Present in around 48% of the population |
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What You'll Learn
FPL is a long muscle in the forearm and hand
The flexor pollicis longus (FPL) is a long muscle in the forearm and hand. It is one of the three deep flexors of the volar compartment of the forearm. The FPL is located in the deep layer of the anterior compartment of the forearm, alongside the flexor digitorum profundus and pronator quadratus muscles.
The FPL arises from the volar or anterior surface of the radius, extending between the radial tuberosity and the attachment of the pronator quadratus. It then courses along the radial aspect of the volar forearm, forming a long, flat tendon near the wrist. This tendon traverses the carpal tunnel, passing deep to the transverse carpal ligament and inserting into the distal phalanx of the thumb.
The primary function of the FPL is to flex the thumb at the interphalangeal (IP) joint, which is essential for gripping. It is the only muscle that performs this action. Additionally, the FPL flexes the thumb at the metacarpophalangeal (MCP) joint and contributes to radial wrist deviation and wrist flexion.
The FPL is unique to humans, being either rudimentary or absent in other primates. An accessory flexor pollicis longus is present in around 48% of the population. This accessory head, known as Gantzer's muscle, can cause compression of the anterior interosseous nerve. The FPL receives dual blood supply, with its medial part supplied by the anterior interosseous artery (a branch of the ulnar artery) and its lateral part supplied by the radial artery.
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It flexes the thumb at the interphalangeal joint
The flexor pollicis longus (FPL) is a long muscle located in the anterior compartment of the forearm. It is one of the three deep flexors of the volar compartment of the forearm. The FPL is also classified as an extrinsic muscle of the hand because, although it is situated in the forearm, its function is observed in thumb movement.
The FPL originates from the mid-half of the anterior surface of the radius and adjacent half of the interosseous membrane. It also sometimes takes its origin from the medial epicondyle of the humerus, the coronoid process of the ulna, and the flexor digitorium superficialis. The FPL muscle forms a flattened large tendon that courses through the carpal tunnel, crossing three joints of the hand to attach at the base of the distal phalanx. It is innervated by the median nerve via the anterior interosseous nerve (7th and 8th cervical nerve root).
The FPL is the only muscle that flexes the interphalangeal (IP) joint of the distal phalanx of the thumb. This function is essential for activities that require hand gripping. The FPL also serves as an accessory flexor of the metacarpophalangeal (MCP) joint of the proximal phalanx and the carpometacarpal (CMC) joints of the first metacarpal. It may also assist in wrist joint flexion.
The FPL tendon passes through the carpal tunnel, inserting at the volar base of the distal thumb phalanx. The thumb's flexor pulley system consists of three annular ligaments (A1, Av, A2) and one oblique ligament. The FPL tendon passes deep to the A1 pulley overlying the thumb MCP joint, the annular variable ligament, and the oblique ligament of the thumb's proximal phalanx, and the A2 pulley overlying the IP joint.
The FPL is the only tendon that can flex the interphalangeal joint of the thumb. However, proximal muscles must stabilize the CMC and MCP joints so that the FPL glide is directed distally to move the IP joint. This mechanism is essential for achieving full thumb flexion following FPL repair.
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FPL is one of the three deep flexors of the volar compartment of the forearm
The flexor pollicis longus (FPL) is a long muscle located in the forearm and hand that flexes the thumb. It is one of the three deep flexors of the volar compartment of the forearm. The FPL is unique to humans, being either rudimentary or absent in other primates.
The FPL muscle is the primary flexor of the thumb, providing flexion at its metacarpophalangeal (MCP) joint and interphalangeal (IP) joint. It also assists in wrist joint flexion. The FPL muscle originates on the volar surface of the proximal aspect of the radius, and courses along the radial aspect of the volar forearm before transitioning into a long tendinous slip that traverses deep to the transverse carpal ligament as a constituent of the carpal tunnel. The FPL tendon travels through the carpal tunnel, passing deep to the transverse carpal ligament (flexor retinaculum) and inserting distally on the base of the distal phalanx of the thumb.
The FPL muscle is innervated by the median nerve via the anterior interosseous nerve (7th and 8th cervical nerve root). The blood supply to the FPL is from a branch (anterior interosseous artery) of the ulnar artery. The FPL is located lateral to the flexor digitorum profundus, and these two muscles form a groove through which the anterior interosseous nerve, artery, and vein run over the anterior surface of the interosseous membrane.
The FPL is one of the two muscles that make up the third layer of the anterior compartment of the forearm, along with the flexor digitorum profundus. It lies in the same plane as the flexor digitorum profundus and pronator quadratus, and is classified as an extrinsic muscle of the hand as it originates in the forearm but inserts in the hand.
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It receives dual blood supply
The flexor pollicis longus (FPL) muscle is a long muscle in the forearm and hand that flexes the thumb. It is one of the three deep flexors of the volar compartment of the forearm. It is also classified as an extrinsic muscle of the hand as it lies in the forearm but inserts in the hand.
The FPL muscle is the primary flexor of the thumb, providing flexion at its metacarpophalangeal (MCP) joint and interphalangeal (IP) joint. It also contributes to radial wrist deviation and wrist flexion. The FPL muscle receives dual blood supply. Its medial part is supplied by the anterior interosseous artery, a branch of the ulnar artery. The lateral part, on the other hand, receives blood from the radial artery. The FPL may also receive contributions from the median artery if the muscle is well developed.
The FPL muscle originates from the volar or anterior surface of the proximal aspect of the radius. It courses along the radial aspect of the volar forearm before transitioning into a long tendinous slip that traverses deep to the transverse carpal ligament as a constituent of the carpal tunnel. The FPL tendon, now covered by the synovial sheath of the radial bursa, travels through the carpal tunnel passing deep to the transverse carpal ligament (flexor retinaculum).
The FPL tendon continues along the first metacarpal, passing between the two sesamoid bones which reside on the volar aspect of the thumb MCP joint. The FPL tendon and synovial sheath pass deep to the A1 pulley overlying the thumb MCP joint, the annular variable ligament and oblique ligament of the thumb's proximal phalanx, and the A2 pulley overlying the IP joint before inserting at the volar base of the distal thumb phalanx.
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FPL is unique to humans
The flexor pollicis longus (FPL) is a long muscle in the forearm and hand that flexes the thumb. It is one of the three deep flexors of the volar compartment of the forearm. The FPL is unique to humans, being either rudimentary or absent in other primates.
The FPL muscle is the primary flexor of the thumb, providing flexion at its metacarpophalangeal (MCP) joint and interphalangeal (IP) joint. It also serves as an accessory flexor of the metacarpophalangeal joint of the proximal phalanx and the carpometacarpal joints of the first metacarpal. The FPL may also assist in wrist joint flexion. The FPL is innervated by the median nerve via the anterior interosseous nerve (7th and 8th cervical nerve root).
The FPL muscle is one of the two muscles that make up the third layer of the anterior compartment of the forearm, along with the flexor digitorum profundus muscle. It originates from the anterior surface of the radius and adjacent interosseous membrane. The FPL has also been found to take its origin from the medial epicondyle of the humerus, coronoid process of the ulna, and from the flexor digitorum superficialis.
The FPL is quite variable and can occasionally be blended with the flexor digitorum superficialis, flexor digitorum profundus, or pronator teres. In a small part of the population, the FPL can even be absent. The FPL receives nervous supply from the anterior interosseous branch of the median nerve, derived from spinal roots C7 and C8. It receives dual blood supply, with its medial part supplied by the anterior interosseous artery, an indirect branch of the ulnar artery, and its lateral part receiving blood from the radial artery.
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