Athena Vale
The human hand and wrist are a complex network of bones, muscles, nerves, tendons, ligaments, blood vessels, and parts of the lymphatic system. The wrist and hand muscles are primarily located in the forearm, and they work together to help you move your hand and fingers. The muscles in the forearm that act on the wrist and hand are referred to as extrinsic muscles, while muscles within the wrist and hand are called intrinsic muscles. The wrist shares muscles with the forearm, and the muscles that control wrist abduction include the extensor carpi radialis longus and brevis, which are a pair of muscles located on the side of the forearm, allowing them to control wrist extension and abduction.
| Characteristics | Values |
|---|---|
| Muscles controlling wrist abduction | Extensor Carpi Radialis Longus and Brevis |
| Extensor Retinaculum | |
| Abductor Pollicis Longus | |
| Extensor Carpi Ulnaris | |
| Extensor Digitorum | |
| Extensor Pollicis Brevis |
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What You'll Learn
Flexor Carpi Ulnaris
The flexor carpi ulnaris (FCU) is a muscle of the forearm that flexes and adducts at the wrist joint. It is the most medial flexor muscle in the superficial compartment of the forearm. The FCU is a long muscle, originating near the elbow and passing through into the wrist, attaching to one of the carpal bones in the wrist.
The FCU has two heads; a humeral head and an ulnar head. The humeral head originates from the medial epicondyle of the humerus via the common flexor tendon. The ulnar head originates from the olecranon and the upper two-thirds of the dorsal border of the ulna. The FCU inserts into the pisiform, hook of the hamate, and the anterior surface of the base of the fifth metacarpal.
The FCU is the only muscle in the anterior compartment that is fully innervated by the ulnar nerve. The ulnar nerve passes between the humeral and ulnar heads of the FCU. The FCU receives its arterial blood supply via three routes: the ulnar collateral arteries, and the anterior and posterior ulnar recurrent arteries.
The FCU can be palpated by locating the bony landmarks associated with the muscle. These include the medial epicondyle (origin), the olecranon process (to identify the ulna), and the pisiform bone (insertion). To locate the FCU muscle, a person can be asked to perform ulnar deviation and wrist flexion simultaneously.
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Extensor Carpi Radialis Longus and Brevis
The wrist is a complex joint that allows the hand to reposition itself. The hand and wrist are a complicated network of bones, muscles, nerves, tendons, ligaments, blood vessels, and parts of the lymphatic system. The wrist shares muscles with the forearm, and these muscles are grouped into flexion and extension muscles.
The Extensor Carpi Radialis Longus and Extensor Carpi Radialis Brevis are a pair of muscles located on the side of the forearm. Together, they control extension and abduction of the wrist. The Extensor Carpi Radialis Brevis is the shorter of the two muscles, and it sits deep to the Extensor Carpi Radialis Longus. The Extensor Carpi Radialis Brevis originates from the lateral epicondyle of the humerus via the common extensor tendon. Some fibres also originate from the lateral intermuscular septum, a thick aponeurosis that covers the muscle itself, and from the radial collateral ligament. The muscle courses inferiorly, giving 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, and inserts into the posterior aspect of the base of the third metacarpal bone. The Extensor Carpi Radialis Brevis is an extensor and an abductor of the hand at the wrist joint.
The Extensor Carpi Radialis Longus 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. It is a fusiform muscle that forms a flattened tendon, which runs distally over the lateral surface of the radius. The Extensor Carpi Radialis Longus is partly overlapped by the Brachioradialis muscle, and these muscles often blend together. The tendon of the Extensor Carpi Radialis Longus, along with that of the Extensor Carpi Radialis Brevis, is crossed by the tendons of the Abductor Pollicis Brevis and Extensor Pollicis Brevis. The tendons of the Extensor Carpi Radialis Longus and Brevis pass deep to the extensor retinaculum in a common synovial sheath and continue along the radius.
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Flexor Digitorum Superficialis
The flexor digitorum superficialis is a key muscle controlling wrist and finger flex. It is an extrinsic flexor muscle of the fingers at the proximal interphalangeal joints. It is the largest muscle of the anterior compartment of the forearm. It is also known as flexor digitorum sublimis or flexor digitorum communis sublimis.
The flexor digitorum superficialis is divided into two heads: the humeroulnar head and the radial head. The muscle originates from the humerus and the radius, splitting into four tendons at the wrist which travel through the carpal tunnel and attach to the fingers. The muscle fibres separate into two planes, superficial and deep, with the superficial plane inserting into digits 3 and 4, and the deep plane inserting into digits 2 and 5. The deep plane also gives off a small slip that joins the tendon of the superficial layer, inserting into digit 2.
The flexor digitorum superficialis is innervated by the median nerve (C7, C8, T1). Its main function is flexion of the digits 2-5 at the metacarpophalangeal and proximal interphalangeal joints. The muscle is relatively common to be missing from the little finger, which can cause issues when diagnosing a little finger injury.
To test the flexor digitorum superficialis, one finger is flexed at the proximal interphalangeal joint against resistance, while the remaining three fingers are held fully extended to inactivate the flexor digitorum profundus.
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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.
The APL's major function is to abduct the thumb at the wrist, or carpometacarpal joint, thereby 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 abducts and extends the thumb at the first metacarpophalangeal joint. This action is seen in activities such as bowling and shovelling. Working together with the long and short extensors of the thumb, the APL also helps to fully extend the thumb at the metacarpophalangeal joint.
The APL 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. Blood supply to the APL comes from the interosseous branches of the ulnar artery. The proximal part of the muscle is supplied by the lateral branch of the posterior interosseous artery. The distal part is vascularised by a perforating branch of the anterior interosseous artery.
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 APL tendon 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 radius. The anatomical snuffbox is traversed by the neurovascular structures of the hand; the superficial branch of the radial nerve, the radial artery and cephalic vein.
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Extrinsic and intrinsic muscles
The human hand and wrist are complex parts of the body that enable us to touch and control objects. They are made up of a complicated network of bones, muscles, nerves, tendons, ligaments, and blood vessels.
The muscles that control the wrist and hand are divided into two groups: extrinsic and intrinsic muscles. The forearm muscles that act on the wrist and hand are referred to as extrinsic muscles, or external to the hand. The extrinsic muscles of the finger and thumb have smaller moment arms about the wrist axes, and their principal effect is distal to the wrist. However, they contribute significantly to wrist stability. The extrinsic muscle group is called so because the muscle belly originates in the forearm.
The intrinsic muscles, on the other hand, are the muscles within the wrist and hand. They consist of smaller muscles solely located within the various hand osseofascial compartments within the anatomic confines of the wrist and phalanges. These muscles are responsible for various hand functions, such as pinch and grip strength. The intrinsic muscles produce finer, more controlled movements and play an important role in maintaining grip. Understanding the intrinsic hand muscle groups is crucial, as denervation and loss of function may lead to pronounced deficits in hand function.
The radial nerve innervates the finger extensors and the thumb abductor, which extend at the wrist and metacarpophalangeal joints (knuckles) and abduct and extend the thumb. The median nerve innervates the flexors of the wrist and digits, the abductors and opponens of the thumb, and the first and second lumbricals. The ulnar nerve innervates the remaining intrinsic muscles of the hand, including all the interossei and the third and fourth lumbricals.
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Frequently asked questions
The Extensor Carpi Radialis Longus and Brevis control wrist abduction. They are a pair of muscles located on the side of the forearm.
Wrist abduction is one of the movements of the fingers and thumb, along with adduction, extension, and flexion.
These muscles are responsible for controlling extension and abduction of the wrist.
