Athena Vale
The thumb is one of the most important parts of the hand, with its versatility in movement compared to the other digits. The muscles that extend the thumb are the extensor pollicis longus and brevis muscles, which are located in the lower forearm and allow you to extend your thumb, for example, when hitchhiking or giving a thumbs-up. The abductor pollicis brevis, abductor pollicis longus, and adductor pollicis muscles also extend the thumb. The muscles of the thumb can be divided into extrinsic (muscles in the forearm) and intrinsic (muscles in the hand) groups.
| Characteristics | Values |
|---|---|
| Number of muscles in the thumb | 9 |
| Muscle groups | Extrinsic (4 muscles in forearm), Intrinsic (5 muscles in hand) |
| Extrinsic muscles | Abductor pollicis longus, Extensor pollicis brevis, Extensor pollicis longus, Flexor pollicis longus |
| Intrinsic muscles | Abductor pollicis brevis, Flexor pollicis brevis, Opponens pollicis, First dorsal interosseous, Adductor pollicis |
| Innervation for extrinsic muscles | Radial nerve (C6, C7, C8, T1) |
| Innervation for intrinsic muscles | Median nerve (C6, C7, C8, T1), Ulnar nerve (C8, T1) |
| Muscle length | Extensor pollicis longus: 6.7-9.7 cm (2.6-3.8 inches) |
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What You'll Learn
Extensor pollicis longus and brevis muscles
The thumb is controlled by nine skeletal muscles located in the hand and forearm. These muscles enable flexion, extension, adduction, abduction, and opposition of the thumb. The muscles acting on the thumb can be divided into two groups: extrinsic hand muscles and intrinsic hand muscles. The former have their muscle bellies located in the forearm, while the latter have their muscle bellies located in the hand.
The extensor pollicis longus (EPL) is a skeletal muscle located dorsally on the forearm. It is one of the deep forearm extensors that control the movement of the thumb. The EPL arises from the dorsal surface of the ulna and the interosseous membrane, next to the origins of the abductor pollicis longus and extensor pollicis brevis. The EPL tendon passes through the third tendon compartment, lying in an oblique groove on the back of the lower end of the radius. It crosses the wrist close to the dorsal midline before turning towards the thumb using Lister's tubercle on the distal end of the radius as a pulley. The EPL tendon is supplied by branches from various arteries. Before the tendon enters its synovial sheath, arteries from the anterior interosseous artery or its muscular branches enter the tendon. The sheath itself is supplied by the posterior ramus of the same artery. In the metacarpal region, beyond the synovial sheath, the tendon is supplied directly from the radial artery. The EPL receives innervation from the posterior interosseous nerve (C7 and C8), which is a continuation of the deep branch of the radial nerve. The main action of the EPL is to extend the thumb at the metacarpophalangeal and interphalangeal joints. It also assists in adduction of the thumb when the thumb reaches full extension or abduction.
The extensor pollicis brevis (EPB) is a short and slender muscle located in the posterior compartment of the forearm. It is one of the deep extensors of the forearm, along with the supinator, abductor pollicis longus, EPL, and extensor indicis muscles. The EPB originates from the posterior surface of the distal third of the radius, inferior to the origin of the EPL. The origin area extends to the adjacent interosseous membrane. The EPB tendon passes deep to the extensor retinaculum, between the tendons of the abductor pollicis longus and extensor carpi radialis longus. The EPB is innervated by the posterior interosseous nerve (C7 and C8), which is a continuation of the deep branch of the radial nerve. The EPB receives its blood supply from the posterior interosseous artery and perforating branches of the anterior interosseous artery. The main action of the EPB is to extend the thumb at the carpometacarpal and metacarpophalangeal joints, together with the EPL.
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Abductor pollicis longus
The abductor pollicis longus (APL) is an extrinsic muscle of the hand. It is one of the five deep extensors in the forearm, along with the supinator, extensor pollicis brevis, extensor pollicis longus, and extensor indicis. The APL is responsible for facilitating movement and stabilization of the thumb.
The abductor pollicis longus abducts the thumb at the carpometacarpal joint, moving the thumb anteriorly. It also assists in extending and rotating the thumb. By its continued action, it helps to abduct the wrist (radial deviation) and flex the hand. The APL is innervated by the posterior interosseous nerve, which is a continuation of the deep branch of the radial nerve after it passes through the supinator muscle. The radial nerve is a branch of the posterior cord of the brachial plexus. The APL is supplied by the posterior interosseous artery.
The abductor pollicis longus originates from the dorsal sides of both the ulna and the radius, and from the interosseous membrane. Passing through the first tendon compartment, it inserts to the base of the first metacarpal bone. A part of the tendon reaches the trapezium, while another fuses with the tendons of the extensor pollicis brevis and the abductor pollicis brevis. The muscle belly of the APL lies in the distal half of the posterior forearm. It is found deep to extensor digitorum and lateral to extensor pollicis longus muscle, while its tendon is located lateral to the tendon of extensor pollicis brevis.
The tendon of the APL forms the lateral border of the anatomical snuff box, a triangular space found at the base of the thumb. The anatomical snuff box is traversed by the neurovascular structures of the hand, including the superficial branch of the radial nerve, the radial artery, and the cephalic vein.
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Intrinsic and extrinsic muscles
The muscles of the thumb can be divided into extrinsic and intrinsic muscles. The extrinsic muscles are those with their muscle bellies located in the forearm, while the intrinsic muscles are located within the hand itself. There are nine skeletal muscles in total that enable the thumb's flexion, extension, adduction, abduction, and opposition.
The extrinsic muscles of the thumb include the extensor pollicis longus, extensor pollicis brevis, abductor pollicis longus, and abductor pollicis brevis. The extensor pollicis longus extends the terminal phalanx of the thumb and, together with the abductor pollicis brevis and adductor pollicis, can extend the thumb's interphalangeal joint to the neutral position. The extensor pollicis brevis also extends the thumb and, due to its proximity to the long abductor, abducts the thumb as well. The abductor pollicis longus abducts the hand and flexes it towards the palm.
The intrinsic muscles of the thumb can be further divided into two groups: the thenar eminence and other muscles. The thenar eminence refers to the group of muscles on the palm at the base of the thumb, which includes the abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis. The abductor pollicis brevis is the most superficial muscle in the thenar group and is responsible for moving the thumb away from the other four fingers. The flexor pollicis brevis is a two-headed muscle that flexes, adducts, and abducts the thumb, allowing it to oppose the thumb. The opponens pollicis opposes the thumb and assists in adduction. In addition to the thenar eminence muscles, the adductor pollicis and the first dorsal interosseous muscle also influence thumb movement. The adductor pollicis, despite its name, primarily enables rotation and opposition, while the first dorsal interosseous extends from the base of the thumb metacarpal to the radial side of the proximal phalanx of the index finger.
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Adductor pollicis
The adductor pollicis is a muscle in the hand that functions to adduct the thumb. It is the most powerful of the intrinsic muscles of the hand. Its main function is the adduction of the thumb, which is the movement of the thumb towards the index finger from an abducted position. This action is essential for functions that require pinching and gripping. The adductor pollicis also assists in the later stages of opposition of the thumb. This movement is a combination of adduction, medial rotation, flexion, and adduction of the thumb so that it can touch each fingertip of the same hand.
The adductor pollicis has two heads: transverse and oblique. It is a fleshy, flat, triangular, and fan-shaped muscle deep in the thenar compartment beneath the long flexor tendons and the lumbrical muscles at the center of the palm. It is larger than and deeper than the thenar muscles. The oblique head arises by several slips from the capitate bone, the bases of the second and third metacarpals, the intercarpal ligaments, and the sheath of the tendon of the flexor carpi radialis. The transverse head, meanwhile, arises by a broad base from the lower two-thirds of the palmar surface of the third metacarpal bone. The two heads then merge as the fibres travel laterally, forming the tendon of the adductor pollicis, which often contains a sesamoid bone. The muscle ends in a tendon that inserts into the base of the first proximal phalanx as well as its extensor hood.
The adductor pollicis is innervated by the deep branch of the ulnar nerve (C8-T1). It is vascularized by the deep palmar arterial arch, formed by the anastomosis of the radial artery and the deep palmar branch of the ulnar artery. The radial artery passes between the two heads of the adductor pollicis, travelling from the back of the hand into the palm, where it forms the deep palmar arch. The adductor pollicis is an important anatomical landmark for the radial artery, which passes through the two heads of the first dorsal interosseous muscle as it enters the hand.
The adductor pollicis evolved from the contrahens I muscle as man's ancestors' thumbs and big toes became opposable. It might also contain an element of the thumb's interosseous muscle. In the Pan-Homo LCA, the oblique head of the adductor pollicis probably had a relatively small physiological cross-sectional area (PCSA) and both heads probably acted as extensors and adductors at the carpometacarpal joint.
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Flexor pollicis longus and brevis muscles
The flexor pollicis longus is a long muscle of the forearm. It is one of the deep flexors of the forearm, along with the flexor digitorum profundus and pronator quadratus. It originates from a broad area on the radius and adjacent structures, crosses three joints and finally inserts into the distal phalanx of the thumb. The flexor pollicis longus is the only muscle that flexes the interphalangeal joint of the thumb, which makes it vital for activities that require hand gripping. It also flexes the thumb at the metacarpophalangeal joint and contributes to the flexion of the wrist.
The flexor pollicis brevis is a thenar muscle of the hand that flexes the thumb. It is the most medial of the thenar muscles. It lies medial to the abductor pollicis brevis and opponens pollicis muscles, while it is lateral to the adductor pollicis muscle. The flexor pollicis brevis is a two-headed muscle. The superficial head arises on the flexor retinaculum, while the deep head originates on three carpal bones: the trapezium, trapezoid, and capitate. The muscle is inserted onto the radial sesamoid bone of the metacarpophalangeal joint. It acts to flex, adduct, and abduct the thumb, and is therefore also able to oppose the thumb. The flexor pollicis brevis can, rarely, be completely absent at birth due to a congenital issue.
The superficial head of the flexor pollicis brevis receives nervous supply from the recurrent branch of the median nerve, whereas the deep head receives innervation from the deep branch of the ulnar nerve, derived from spinal roots C8 and T1. The flexor pollicis longus receives nervous supply from the anterior interosseous branch of the median nerve, derived from spinal roots C7 and C8. Its medial part is supplied by the anterior interosseous artery, an indirect branch of the ulnar artery, while the lateral part receives blood from the radial artery.
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Frequently asked questions
The muscles that extend the thumb are the extensor pollicis longus, extensor pollicis brevis, abductor pollicis longus, and abductor pollicis brevis.
The extensor pollicis longus muscle is located in the forearm. It arises from the dorsal surface of the ulna and the interosseous membrane.
The extensor pollicis longus muscle is responsible for extending the terminal phalanx of the thumb. It is the longer tendon of the two tendons that pop up when the thumb is extended.
The abductor pollicis longus abducts and extends the MCP joint of the thumb. It is one of the four extrinsic muscles that influence thumb movement.
The adductor pollicis muscle is an intrinsic muscle of the hand that lies in the deepest muscular plane of the palm. Its main function is to adduct the thumb, bringing it into a position of opposition at the center of the palm.
