Maximus Gage
The wrist joint, also known as the radiocarpal joint, is a synovial joint marking the transition between the forearm and the hand. The muscles of the forearm, also known as extrinsic muscles, are responsible for wrist movement, including flexion, extension, adduction, and abduction. This text will focus on the muscles that abduct the wrist, allowing it to move in several directions and making it a highly mobile joint.
| Characteristics | Values |
|---|---|
| Muscles that abduct the wrist | Abductor Pollicis Longus, Flexor Carpi Radialis, Extensor Carpi Radialis Longus and Brevis |
| Flexor Carpi Radialis attachments | Originates from the humerus and attaches to the base of the digits (fingers) |
| Extensor Carpi Radialis Longus and Brevis attachments | Located on the side of the forearm |
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What You'll Learn
Flexor Carpi Radialis
The flexor carpi radialis (FCR) is a muscle in the human forearm that acts to flex and abduct the hand at the wrist. The name of the muscle is derived from Latin, where "carpi" means wrist and "radialis" means radial, or relating to the radius bone in the forearm.
The flexor carpi radialis is a long, thin muscle located in the anterior, or front, part of the forearm. It is one of four muscles in the superficial layer of the anterior compartment of the forearm, along with the pronator teres, flexor carpi ulnaris, palmaris longus, and flexor digitorum superficialis muscles. All of these muscles share the function of flexing the hand on the wrist, which is why the entire compartment is also called the flexor compartment of the forearm.
The flexor carpi radialis originates from the medial epicondyle of the humerus, which is the upper arm bone, and is part of the common flexor tendon. It runs obliquely downwards, just lateral to the flexor digitorum superficialis, and inserts on the anterior aspect of the base of the second metacarpal, with small slips to the third metacarpal and trapezium tuberosity. The tendon of the flexor carpi radialis is visible on the anterior surface of the forearm, just proximal to the wrist, when the wrist is flexed. It is the tendon closest to the thumb.
The main function of the flexor carpi radialis is to provide flexion of the wrist and assist in the abduction of the hand and wrist. Due to its oblique course, the muscle pulls the hand proximally and laterally, resulting in a combined motion of wrist flexion and wrist abduction, or radial deviation. The FCR also contributes to pronation as it crosses the forearm obliquely. Additionally, the FCR has been suggested to act as a dynamic scaphoid stabilizer, as the FCR tendon uses the scaphoid tuberosity as a pulley to reach its distal insertion onto the second metacarpal.
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Extensor Carpi Radialis Longus and Brevis
The extensor carpi radialis longus is a muscle found in the posterior compartment of the forearm. It is one of three primary wrist extensors. It is most effective as a wrist extensor when the elbow is extended and when radial deviation is balanced by the primary ulnar deviator, extensor carpi ulnaris. The muscle is also involved in flexing the elbow joint and is active during fist clenching. The extensor carpi radialis longus is classified as part of the superficial layer of forearm muscles, along with the brachioradialis, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris.
The extensor carpi radialis brevis is an extensor muscle in the posterior superficial compartment of the forearm. It is the prime dorsiflexor of the wrist. The extensor carpi radialis brevis is shorter in length and sits deep to the extensor carpi radialis longus. It is one of seven superficial extensor muscles of the posterior forearm, along with the brachioradialis, extensor carpi radialis longus, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, and anconeus.
The specific action of the extensor carpi radialis brevis is to extend and abduct the hand at the wrist joint. It originates from the lateral epicondyle of the humerus via the common extensor tendon, which is shared with the extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris muscles. The muscle gives off a long tendon in the middle of the forearm, which descends towards the dorsal hand. The tendon passes through a groove on the posterior surface of the radius, deep to the extensor retinaculum. After traversing the extendon retinaculum space, the tendon inserts into the posterior aspect of the base of the third metacarpal bone.
The extensor carpi radialis longus and brevis work together to extend and abduct the wrist. The tendons of these two muscles pass deep to the extensor retinaculum in a common synovial sheath. They also work together with the extensor carpi ulnaris to extend the hand at the wrist joint. The extensor carpi radialis longus and brevis can be palpated in the upper lateral portion of the posterior forearm during wrist extension and abduction movements.
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Abductor Pollicis Longus
The abductor pollicis longus (APL) is a muscle found in the posterior compartment of the forearm. 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 abductor pollicis longus is responsible for facilitating movement and stabilization of the thumb. It is one of the extrinsic muscles of the hand, originating in the forearm.
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 works in conjunction with the long and short extensors of the thumb to fully extend the thumb at the metacarpophalangeal joint. This action is seen in activities such as bowling and shovelling.
The muscle belly of the abductor pollicis longus lies in the distal half of the posterior forearm, deep to the extensor digitorum and lateral to the extensor pollicis longus muscle. Its tendon is located lateral to the tendon of the extensor pollicis brevis and forms the lateral border of the anatomical snuffbox. This is a triangular space found at the base of the thumb, distal and posterior to the styloid process of the radius. The abductor pollicis longus is innervated by the posterior interosseous nerve (C7, C8), which is a continuation of the deep branch of the radial nerve. The radial nerve is a branch of the posterior cord of the brachial plexus.
The abductor pollicis longus originates from the posterior surface of the proximal half of the radius, ulna, and intervening interosseous membrane, just inferior to the insertion of the anconeus muscle. From here, the muscle courses inferolaterally towards the radial side of the hand, becoming more superficial as it enters the distal third of the forearm. Just proximal to the wrist, the muscle gives off a narrow tendon, which passes through a groove on the lateral side of the distal end of the radius, accompanied by the tendon of the extensor pollicis brevis.
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Flexor Carpi Ulnaris
The flexor carpi ulnaris (FCU) is a muscle in the forearm that flexes and adducts at the wrist joint. It is the most powerful wrist flexor and is the only anterior forearm compartment muscle completely innervated by the ulnar nerve. The FCU tendon is a landmark for locating the ulnar nerve and artery during surgery, as these structures lie immediately lateral to the muscle.
The FCU originates from two separate heads, the humeral head and the ulnar head, which are connected by a tendinous arch. The humeral head arises from the medial epicondyle of the humerus via the common flexor tendon. The ulnar head originates from the olecranon and the proximal part of the ulna by an aponeurosis. Between the two heads passes the ulnar nerve and ulnar artery.
The FCU inserts onto the pisiform, hook of the hamate, and the base of the fifth metacarpal. The muscle is attached to the hook of the hamate via the pisohamate ligament and to the fifth metacarpal bone through the pisometacarpal ligament. The FCU is the most medial among the superficial anterior forearm compartment muscles.
The FCU is involved in flexing and adducting the hand at the wrist. When the FCU contracts with the flexor carpi radialis and palmaris longus, it produces flexion of the hand at the wrist joint. However, when it contracts with the extensor carpi ulnaris muscle in the posterior compartment, their counteracting forces produce adduction of the hand at the wrist, also known as ulnar deviation or ulnar flexion.
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Extensor Digitorum
The extensor digitorum muscle is a long muscle located in the posterior compartment of the forearm in humans and other animals. It is the most superficial muscle of the posterior forearm, and is located medial to the extensor carpi radialis brevis muscle and lateral to the extensor digiti minimi and extensor carpi ulnaris muscles. The extensor digitorum muscle arises from the lateral epicondyle of the humerus, by the common tendon, and from the intermuscular septa between it and the adjacent muscles. It is innervated by the posterior interosseous nerve, which is a branch of the radial nerve.
The extensor digitorum muscle is responsible for extending the medial four digits of the hand. It extends the phalanges, the wrist, and the elbow, and separates the fingers as it extends them. It acts on the proximal phalanges, extending the metacarpophalangeal joint, and the extension of the proximal and distal interphalangeal joints is mediated by the dorsal and palmar interossei and lumbricals of the hand. The extensor digitorum muscle also participates in the anatomy of the grip, as it contributes to the opening of the hand and letting go of an object.
The tendon of the extensor digitorum muscle divides into four in the distal forearm, and these tendons pass through the 4th extensor compartment at the wrist and enter the dorsum of the hand, passing deep to the extensor retinaculum. The tendons then diverge on the back of the hand and are inserted into the middle and distal phalanges of the fingers. Opposite the metacarpophalangeal articulation, each tendon is bound by fasciculi to the collateral ligaments and serves as the dorsal ligament of this joint.
The extensor digitorum muscle is vascularized by the branches of three different arteries: the anterior and posterior interosseous arteries, which are branches of the common interosseus artery that arises from the ulnar artery, and the radial recurrent artery, which is a branch of the radial artery.
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Frequently asked questions
Abduction of the wrist is produced by the abductor pollicis longus, flexor carpi radialis, and extensor carpi radialis longus and brevis.
Wrist abduction is one of the movements of the wrist joint, which is a highly mobile joint allowing the hand to move in several directions.
The muscles of wrist abduction are responsible for moving the hand in multiple directions. They also contribute to wrist extension.
