Maximus Gage
The wrist is a complex joint that allows for a wide range of movements. It is a series of small joints that connect the radius and ulna in the forearm to the carpals in the hand. The wrist joint is highly mobile, allowing for flexion, extension, radial deviation, and ulnar deviation. Flexion, or bending the wrist towards the palm, is produced mainly by the flexor carpi ulnaris, flexor carpi radialis, and flexor digitorum superficialis. These muscles, along with several others, are responsible for the flexion movement of the wrist, allowing us to perform various daily activities.
| Characteristics | Values |
|---|---|
| Number of muscles that flex the wrist | 6 |
| Names of muscles that flex the wrist | Flexor carpi radialis, flexor carpi ulnaris, palmaris longus, flexor digitorum superficialis, flexor digitorum profundus, flexor pollicis longus |
| Location of muscles that flex the wrist | Forearm |
| Function of muscles that flex the wrist | Allow for wrist movements like flexion, extension, radial deviation, and ulnar deviation |
| Tendons associated with wrist muscles | Long and slender, anchored by flexor retinaculum and extensor retinaculum |
| Bones associated with wrist muscles | Radius, ulna, carpals, phalanges (finger bones) |
| Joint type | Ellipsoidal (condyloid) type synovial joint |
| Joint function | Allows movement along two axes, enabling flexion, extension, adduction, and abduction |
| Common injuries | Tendonitis, carpal tunnel syndrome, sprains, fractures (e.g., Colles' fracture), lateral epicondylitis |
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What You'll Learn
Forearm muscles that flex the wrist
The wrist is a series of small joints that connect the radius and ulna (the two bones in the forearm) to the carpals in the hand. The wrist joint, or radiocarpal joint, marks the transition between the forearm and the hand.
There are six main muscles that flex the wrist. These muscles are the flexor carpi radialis, flexor carpi ulnaris, palmaris longus, flexor digitorum superficialis, flexor digitorum profundus, and flexor pollicis longus. The first three muscles originate in the humerus, cross the forearm, and extend through the wrist via tendons that attach to the bones of the hand. The latter three muscles start in the forearm, and their tendons attach to the phalanges (finger bones).
The flexor carpi ulnaris and flexor carpi radialis are the primary muscles responsible for flexion, or bending the wrist towards the palm. The flexor digitorum superficialis assists with this movement.
Several muscles in the forearm also control the rotation of the wrist and hand. When the elbows are bent at a 90-degree angle, the supinator muscle rotates the palm upwards. The pronator teres and pronator quadratus muscles work in the opposite direction, turning the palm downwards.
The anatomical complexity and versatility of the wrist allow for a wide range of movements and dexterity.
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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 forearm's superficial compartment. The FCU has two heads: a smaller humeral head and a larger ulnar head. The former originates from the medial epicondyle of the humerus via the common flexor tendon, while the latter originates from the olecranon and upper two-thirds of the dorsal border of the ulna. The ulnar nerve and ulnar artery pass between the two heads.
The FCU inserts onto the pisiform, hook of the hamate, and the anterior surface of the base of the fifth metacarpal. This muscle flexes and adducts the hand at the wrist joint. It is innervated by the ulnar nerve, with corresponding spinal nerves C8 and T1. The tendon of the FCU is the most medial of the tendons in the distal forearm, just before the wrist.
The FCU is the only muscle in the anterior compartment fully innervated by the ulnar nerve. It receives its arterial blood supply via three routes: proximally, a branch of the posterior ulnar recurrent artery supplies it, while the ulnar collateral arteries and the anterior ulnar recurrent artery also contribute. The FCU tendon insertion is a useful landmark for locating the ulnar nerve and artery, which lie lateral to the tendon at the wrist joint.
The FCU can be palpated by identifying bony landmarks such as the medial epicondyle, olecranon process, and pisiform bone. Patients can then be instructed to perform ulnar deviation while flexing the wrist against resistance to locate the FCU muscle. The FCU can be strengthened by exercises like wrist curls with dumbbells and using a wrist roller.
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Flexor carpi radialis
The flexor carpi radialis (FCR) is a long, thin muscle in the forearm that acts to flex and abduct the hand and wrist. 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: 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. In the lower third of the forearm, it gives off a long tendon that passes below the flexor retinaculum into the palmar surface of the hand.
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 innervation of this muscle is provided by the median nerve (C6-C7). The flexor carpi radialis mainly receives its blood supply (high up in the forearm) via the anterior or posterior ulnar recurrent artery, with the rest of its nutritional needs fulfilled by 6-8 branches of the radial artery.
The FCR muscle has been suggested to act as a dynamic scaphoid stabilizer. The FCR tendon uses the scaphoid tuberosity as a pulley to reach its distal insertion onto the second metacarpal. It has been hypothesized that FCR muscle contraction generates a dorsally directed vector that resists the scaphoid from rotating into flexion. Flexor tendon ruptures in the wrist are uncommon, but FCR tendon rupture can occur in rheumatoid patients, following cortisone injection for tenosynovitis, and following trauma.
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Extensor muscles
The extensor muscles are located in the forearm, with long tendons connecting them to the bones in the hand. These muscles extend or open flat the joints in the hand. The extensor retinaculum anchors the extensor tendons and supports the posterior structure of the wrist.
The extrinsic extensor muscles of the hand are located in the back of the forearm and are considered extrinsic because they are located outside the hand. These muscles include the extensor carpi radialis longus (ECRL), extensor carpi radialis brevis (ECRB), extensor digitorum (ED), extensor digiti minimi (EDM), extensor carpi ulnaris (ECU), abductor pollicis longus (APL), extensor pollicis brevis (EPB), extensor pollicis longus (EPL), and extensor indicis (EI).
The ECRL has the most proximal origin of the extrinsic hand extensors, originating just distal to the brachioradialis at the lateral supracondylar ridge of the humerus. The APL originates from the lateral part of the dorsal surface of the body of the ulna, while the EPB arises from the radius distal to the APL and from the dorsal surface of the radius. The EPL arises from the dorsal surface of the ulna, and the EI arises from the distal third of the dorsal part of the body of the ulna. The APL, EPB, EPL, and EI all have an additional origin at the interosseus membrane.
The wrist extensor muscles are responsible for extending or bending the wrist backward. These muscles include the extensor carpi radialis longus, extensor carpi radialis brevis, extensor carpi ulnaris, and extensor digitorum. Strong wrist extensor muscles are important for stability and control, functionality, and injury prevention. They help stabilize the wrist joint during activities involving gripping or lifting objects, improve functional movements of the hand and wrist, and prevent overuse injuries and conditions like tendinitis or repetitive strain injuries.
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Abduction and adduction
The wrist is a highly mobile joint, allowing for movement along two axes. This means that flexion, extension, adduction, and abduction can all occur at the wrist. The wrist joint is formed by an articulation between the distal end of the radius and the articular disk, and the proximal row of the carpal bones (excluding the pisiform bone).
Adduction of the wrist is produced by the extensor carpi ulnaris and flexor carpi ulnaris muscles. The extensor carpi ulnaris originates from the humerus and attaches to the base of the hand. The flexor carpi ulnaris, meanwhile, is a long muscle that originates near the elbow and passes through the wrist, attaching to one of the carpal bones in the wrist.
Abduction of the wrist is produced by the abductor pollicis longus (APL), flexor carpi radialis, and extensor carpi radialis longus and brevis muscles. The APL is one of the primary radial deviators of the wrist due to its insertion at the base of the first metacarpal and its large moment arm about the radioulnar deviation axis. The flexor carpi radialis is a long muscle that originates near the elbow and passes through the wrist, attaching to the base of the digits. The extensor carpi radialis longus and brevis muscles are the primary extensors of the wrist.
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Frequently asked questions
Wrist flexion, or bending the wrist towards the palm, is produced mainly by the flexor carpi ulnaris and flexor carpi radialis, with assistance from the flexor digitorum superficialis.
Three other muscles involved in wrist flexion are the flexor digitorum profundus, flexor pollicis longus, and palmaris longus. These muscles start in the forearm and extend through the wrist via tendons that attach to bones in the hand.
The muscles involved in wrist flexion are very active in daily activities and are prone to tendonitis. It is important to stretch these muscles before repetitive activities such as working on a computer or texting.
