Dominic Stone
The wrist joint, also known as the radiocarpal joint, is a highly mobile synovial joint that allows for movement along two axes, including flexion, extension, adduction, and abduction. While flexion is produced by the flexor carpi ulnaris and flexor carpi radialis, abduction is caused by the abductor pollicis longus, flexor carpi radialis, and extensor carpi radialis longus and brevis. These muscles, along with other muscles in the forearm, are responsible for the movement of the wrist and are referred to as extrinsic muscles.
| Characteristics | Values |
|---|---|
| Muscles responsible for wrist abduction | Abductor Pollicis Longus, Flexor Carpi Radialis, Extensor Carpi Radialis Longus and Brevis |
| Muscle attachments | Originate from the humerus and attach to the base of the digits (fingers) |
| Muscle actions | Flexion, extension, and abduction at the wrist |
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What You'll Learn
Extensor Carpi Radialis Longus and Brevis
The extensor carpi radialis longus and brevis are two of the three primary wrist extensors. They are both located in the forearm, with the extensor carpi radialis longus occupying the posterior compartment and the brevis located in the radial (or lateral) part of the forearm. The brevis sits deep to the longus and is the shortest of the two muscles.
The extensor carpi radialis longus originates from the lateral supracondylar ridge of the humerus and the anterior aspect of the lateral intermuscular septum of the arm. A small portion of its fibres also originate from the common extensor tendon attached to the lateral epicondyle of the humerus. The muscle belly extends to the middle of the forearm, where it is replaced by a flat tendon that travels distally along the lateral surface of the radius.
The extensor carpi radialis brevis originates from the common extensor tendon attached to the lateral epicondyle of the humerus. It also shares a common origin with the extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris muscles. Some fibres of the brevis originate from the lateral intermuscular septum and the radial collateral ligament. The muscle gives off a long tendon in the middle of the forearm, which descends towards the dorsal hand.
The tendons of both muscles travel together towards the radial styloid process, deep to the tendons of the abductor pollicis longus and extensor pollicis brevis muscles. Proximal to the wrist, the tendons pass behind the radial styloid process within a common synovial sheath and continue along the radiocapitellar joint, where they are crossed by the tendons of the abductor pollicis brevis and extensor pollicis brevis. The tendons then insert into the posterior aspect of the base of the second and third metacarpal bones.
The extensor carpi radialis longus and brevis work together to produce wrist extension and abduction (radial deviation). They are active during fist clenching and may also help to flex the elbow joint.
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Extensor Carpi Ulnaris
The extensor carpi ulnaris (ECU) is a skeletal muscle located on the ulnar side of the forearm. It is a fusiform muscle in the posterior forearm, spanning between the elbow and the base of the little finger. The extensor carpi ulnaris is the most medial muscle of the posterior forearm, originating from the lateral epicondyle of the distal humerus and the posterior aspect of the ulna. It then inserts onto the dorsal base of the fifth metacarpal, passing through the sixth compartment of the extensor retinaculum.
The extensor carpi ulnaris plays a crucial role in wrist and forearm function, contributing to both extension and adduction of the hand at the wrist. Its contraction results in a combined extension and adduction (ulnar deviation) of the hand. Working together with other muscles, such as the extensor carpi radialis brevis and extensor carpi radialis longus, the extensor carpi ulnaris helps maintain a balanced extension of the wrist. This is important for activities that require a strong grip or clenched fist, such as tennis backhands.
The extensor carpi ulnaris is susceptible to injuries, especially in athletes who engage in activities with forceful and repetitive wrist movements, such as gripping, throwing, or racket sports. Tennis elbow is a common injury associated with the extensor carpi ulnaris, causing pain when shaking hands or gripping objects. Repetitive flexion and extension of the wrist can lead to tenosynovitis, an inflammation of the tendon and its sheath. Overuse of the ECU may also result in tendinopathy, causing painful stiffness and thickening of the tendon.
The blood supply to the extensor carpi ulnaris muscle is provided by branches of the radial recurrent and posterior interosseous arteries, which are branches of the radial and ulnar arteries, respectively. The posterior interosseous nerve (C7 and C8), a branch of the deep division of the radial nerve, innervates the extensor carpi ulnaris.
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Flexor Carpi Radialis
The flexor carpi radialis (FCR) is a long, thin muscle located in the anterior 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 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, via the common flexor tendon, and surrounding fascia (antebrachial fascia and intermuscular septa). This common flexor tendon is a common origin for the six long flexor muscles in the forearm, including the flexor carpi radialis, palmaris longus, flexor carpi ulnaris, pronator teres, flexor digitorum superficialis, and profundus. From the medial epicondyle, the muscle belly courses obliquely, crossing from the ulnar to the radial part of the forearm.
The flexor carpi radialis inserts at the bases of the second and third metacarpal bones. 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 seen most lateral, closest to the thumb. The radial artery runs between the tendons of the flexor carpi radialis and brachioradialis muscles, marking a common site for its palpation to measure someone's radial pulse.
The primary 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 flexor carpi radialis pulls the hand proximally and laterally, resulting in a combined motion of wrist flexion and wrist abduction (radial deviation). It also acts 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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Flexor Carpi Ulnaris
The flexor carpi ulnaris (FCU) is a muscle in the forearm that flexes and adducts the wrist joint. It is the most medial flexor muscle in the forearm, located just before the wrist. The FCU has two heads: a smaller humeral head and a larger ulnar head. The humeral head originates from the medial epicondyle of the humerus, while the ulnar head originates from the olecranon and proximal part of the posterior border of the ulna.
The FCU is involved in flexing and adducting the hand at the wrist. It works alongside the flexor carpi radialis to flex the wrist and with the extensor carpi ulnaris to adduct the wrist. The FCU is the only muscle in the anterior compartment of the forearm that is fully innervated by the ulnar nerve. The ulnar nerve passes between the two heads of the FCU, along with the ulnar artery.
The FCU tendon is the most medial of the tendons in the wrist region and can be palpated beneath the skin proximal to the wrist joint. It is a common landmark for locating the ulnar nerve and artery, which lie lateral to the tendon at the wrist joint. The FCU is also associated with various pathologies, such as medial epicondylalgia and Volkmann's contracture, which can lead to impaired function in the affected limb.
The FCU can be strengthened through exercises such as wrist rollers and wrist curls with dumbbells, which help prevent injury to the ulnar collateral ligament of the elbow joint.
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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 APL is one of the extrinsic muscles of the hand, and its primary function is to abduct the thumb at the wrist (carpometacarpal joint), moving the thumb anteriorly. This action helps in abducting the wrist (radial deviation) and flexing the hand.
The APL originates from the posterior surface of the proximal half of the radius, ulna, and intervening interosseous membrane, located just inferior to the insertion of the anconeus muscle. The muscle then 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 APL 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.
The APL tendon forms the lateral border of the anatomical snuffbox, a triangular space found at the base of the thumb, distal and posterior to the styloid process of the radius. This space is traversed by the neurovascular structures of the hand, including the superficial branch of the radial nerve, the radial artery, and the cephalic vein. The APL is innervated by the posterior interosseous nerve (C7, C8), a continuation of the deep branch of the radial nerve. The blood supply to the APL comes from the interosseous branches of the ulnar artery.
The APL plays a crucial role in facilitating movement and stabilization of the thumb. It helps produce mid-extension and abduction of the thumb at the first metacarpophalangeal joint, as seen in activities such as bowling and shovelling. Working together with the long and short extensors of the thumb, the APL also assists in fully extending the thumb at the metacarpophalangeal joint.
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Frequently asked questions
The muscles that produce wrist abduction include the abductor pollicis longus, flexor carpi radialis, and extensor carpi radialis longus and brevis.
Wrist abduction is one of the movements that can occur at the wrist joint, along with flexion, extension, and adduction.
The wrist joint, or radiocarpal joint, is a synovial joint marking the transition between the forearm and the hand. It is a highly mobile joint, allowing the hand to move in several directions.
Other muscles in the wrist and forearm include the palmaris longus, flexor digitorum superficialis, flexor carpi ulnaris, extensor digitorum, and extensor digiti minimi.
