Maximus Gage
The human hand is capable of a wide range of movements, from writing and typing to playing musical instruments and gripping a ball. These movements are made possible by the contraction of various muscles, both within the hand (intrinsic hand muscles) and those that originate from the forearm with tendon attachments to the hand (extrinsic hand muscles). This article will focus on the muscles that flex the hand, including the long flexor muscles of the hand, the thenar muscles, and the lumbricals.
| Characteristics | Values |
|---|---|
| Number of muscles in the hand and forearm | More than 30 |
| Number of extrinsic hand muscles | 6 |
| Extrinsic hand muscles' origin | Forearm |
| Flexor carpi radialis muscle's origin | Medial epicondyle of the humerus |
| Flexor carpi ulnaris muscle's origin | Medial epicondyle and the medial border of the olecranon |
| Flexor pollicis longus muscle's origin | Anterior surface of the radius |
| Flexor digitorum profundus muscle's origin | Proximal end of the radius and ulnar |
| Flexor digitorum superficialis muscle's origin | Medial epicondyle (elbow bone) |
| Palmaris longus muscle's origin | Humerus of the upper arm |
| Thenar muscle group's location | Base of the thumb |
| Number of muscles in the thenar group | 3 |
| Abductor pollicis brevis' function | Pulls the thumb away from the index finger |
| Flexor pollicis brevis' function | Bends the thumb toward the small finger |
| Opponens pollicis' function | Brings the thumb away from the fingers to grasp objects |
| Number of lumbrical muscles | 4 |
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What You'll Learn
The role of the flexor carpi radialis muscle
The flexor carpi radialis is a long, thin muscle located in the anterior forearm. It is one of the six long flexor muscles of the hand that originate in the forearm. The other five muscles are the flexor carpi ulnaris muscle, the flexor pollicis longus muscle, the flexor digitorum profundus muscle, the flexor digitorum superficialis muscle, and the palmaris longus muscle.
The flexor carpi radialis originates from the medial epicondyle of the humerus and passes obliquely downwards to the lateral side of the forearm. It is part of the common flexor tendon, which is a common origin for all six long flexor muscles in the forearm. The muscle belly of the flexor carpi radialis 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 into the palmar surface of the hand. This tendon is visible on the anterior surface of the forearm, just proximal to the wrist, when the wrist is flexed.
The primary role of the flexor carpi radialis is to flex and abduct the hand and wrist. Due to its oblique course, the flexor carpi radialis pulls the hand proximally and laterally, resulting in wrist flexion and wrist abduction (radial deviation). It works in synergy with the flexor carpi ulnaris and palmaris longus muscles to produce a balanced flexion of the hand. Additionally, it assists in moving the wrist towards the thumb.
The flexor carpi radialis is a relatively superficial muscle, and it lies deep to the forearm skin and superficial to the flexor digitorum superficialis muscle. It is also medial to the pronator teres in its proximal part and to the brachioradialis in its distal part. The radial artery runs between the tendons of the flexor carpi radialis and brachioradialis muscles, providing a common site for palpation to measure an individual's radial pulse.
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The flexor carpi ulnaris muscle function
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 the most powerful wrist flexor and the only anterior forearm compartment muscle completely innervated by the ulnar nerve. The ulnar nerve enters the forearm between the two heads of the FCU. The FCU tendon is a useful landmark for locating the ulnar nerve and artery during surgery, as they lie immediately lateral to the muscle.
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 medial margin of the olecranon of the ulna and the upper two-thirds of the dorsal border of the ulna by an aponeurosis. The FCU inserts onto the pisiform, hook of the hamate (via the pisohamate ligament) and the anterior surface of the base of the fifth metacarpal (via the pisometacarpal ligament).
The FCU flexes and adducts the hand at the wrist joint. It acts in tandem with the flexor carpi radialis to flex the wrist and with the extensor carpi ulnaris to adduct the wrist. The FCU is susceptible to involvement in Volkmann's contracture, where ischemic damage compromises the FCU, leading to fibrosis and contracture. This constriction can result in deformities and impaired function in the affected limb.
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). After identifying these landmarks, the patient is asked to perform ulnar deviation and wrist flexion simultaneously, which will help locate the FCU muscle.
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Flexor pollicis longus muscle actions
The flexor pollicis longus is a deep forearm flexor that originates from the anterior surface of the radius. It is one of the six long flexor muscles that originate in the forearm but have tendon attachments in the hand. The flexor pollicis longus muscle is the primary flexor of the thumb, allowing for flexion at the interphalangeal (IP) joint and the metacarpophalangeal (MCP) joint. This muscle is responsible for flexing the thumb towards the palm and is vital for activities that require hand gripping.
The flexor pollicis longus is located in the anterior compartment of the forearm, alongside the flexor digitorum profundus and pronator quadratus. It is classified as an extrinsic muscle of the hand due to its function in thumb movement, despite being situated in the forearm. The muscle belly of the flexor pollicis longus is found in the forearm, while its tendon attaches in the hand, specifically at the base of the distal phalanx of the thumb on the palmar surface.
The flexor pollicis longus muscle also contributes to radial wrist deviation and wrist flexion. It passes through the carpal tunnel, crossing three joints of the hand before attaching at the distal phalanx. The muscle receives its blood supply from the anterior interosseous artery, a branch of the ulnar artery. The anterior interosseous nerve, a branch of the median nerve (specifically the seventh and eighth cervical nerve roots), innervates the flexor pollicis longus.
The flexor pollicis longus is quite variable in structure and can occasionally be blended with other muscles such as the flexor digitorum superficialis, flexor digitorum profundus, or pronator teres. In some individuals, the flexor pollicis longus may even be absent. The presence of an accessory head, known as Gantzer's muscle, has been observed in some cases, with origins from the medial epicondyle of the humerus, the coronoid process of the ulna, or the flexor digitorum superficialis.
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Flexor digitorum superficialis actions
The flexor digitorum superficialis (FDS) is a muscle in the anterior compartment of the forearm, also known as the volar compartment. It is the largest muscle in this compartment. The FDS is an extrinsic flexor muscle of the fingers at the proximal interphalangeal joints. The FDS has two heads: the humeroulnar and the radial. The median nerve and ulnar artery pass between these two heads.
The FDS has four independent muscle bellies, from which four tendons arise. These tendons attach to the middle phalanges of the second to fifth digits of the hand. The FDS is responsible for flexing the middle joint of each finger (excluding the thumb). The independence of each finger's FDS contributes to the hand's skill in performing tasks requiring dexterity, such as using chopsticks.
The FDS is tested by asking a patient to flex the proximal interphalangeal joint of one of the digits from the second to the fifth, while the other digits are held in extension. This isolates the FDS and allows for the assessment of its function and strength.
The FDS is sometimes considered the deepest part of the superficial layer of the anterior compartment of the forearm. However, some sources classify it as an independent middle or intermediate layer of the compartment, located between the superficial and deep groups of muscles.
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The palmaris longus muscle's role
The palmaris longus muscle is a long, slender muscle, usually present in the superficial volar compartment of the forearm. It is one of the six long flexor muscles that originate in the forearm but have tendon attachments in the hand. The other five muscles are the flex carpal radialis muscle, the flexor carpal ulnaris muscle, the flexor pollicis longus muscle, the flexor digitorum profundus muscle, and the flexor digitorum superficialis muscle.
The palmaris longus muscle is the most superficial muscle of the superficial forearm flexors and is found deep within the forearm skin. It extends from the distal humerus to the root of the hand and ends in a slender, flattened tendon. This muscle provides weak flexion of the second to fifth metacarpophalangeal joints and assists in thumb abduction movements, which are necessary to open the hand. It also aids in flexion of the wrist, along with the flexor carpi ulnaris and flexor carpi radialis muscles. The palmaris longus muscle is unique in that it exhibits a high degree of anatomical variation, with some individuals lacking this muscle in one or both forearms.
The palmaris longus muscle is innervated by the median nerve and plays a crucial role in the anatomy of the grip. Its tendon is of significant importance in surgery, particularly in tendon grafts for the wrist and hand. The length and diameter of the palmaris longus tendon make it ideal for use in tendon grafts, and it can be utilised without causing any functional deformities. Additionally, the palmaris longus muscle has been employed in the correction of claw-finger deformities and opponensplasty, as well as in radial palsy to substitute for paralysed lumbricals.
The palmaris longus muscle is a versatile and valuable anatomical structure, contributing to hand and wrist function and serving as a valuable resource in surgical procedures. Its absence in some individuals highlights the fascinating variability in human anatomy.
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Frequently asked questions
The muscles that flex the hand are called the long flexor muscles of the hand. There are six of them: the flex carpal radialis muscle, the flexor carpal ulnaris muscle, the flexor pollicis longus muscle, the flexor digitorum profundus muscle, the flexor digitorum superficialis muscle, and the palmaris longus muscle.
The long flexor muscles are located in the forearm, with their tendon attachments in the hand.
When the flexor carpal radialis muscle contracts, the hand flexes laterally.
When the flexor carpal ulnaris muscle contracts, the hand flexes medially.
The flexor digitorum superficialis bends the middle joint of each finger, except the thumb.
