Forearm muscles

The muscles of the forearm are numerous and have a variety of functions. Most of the muscles are multi-joint, since they act on several joints: the elbow, radioulnar, wrist, and the distal joints of the hand and fingers.

When studying the anatomy of the forearm muscles, they are usually divided into separate groups based on anatomical and functional characteristics. Based on anatomical characteristics, the forearm muscles are divided into the anterior group (flexors) and the posterior group (extensors).

The anterior group consists of 7 flexors of the wrist and fingers and 2 pronators, the posterior group consists of 9 extensors of the wrist and fingers and the first muscle, the supinator. Most of the muscles of the anterior group originate on the medial epicondyle of the humerus and the fascia of the forearm, while the muscles of the posterior group originate on the lateral epicondyle and the fascia of the forearm.

According to their functions, they are divided into:

1. muscles that provide movement in the proximal and distal radioulnar joints - supinator, pronator teres, pronator quadratus, brachioradialis;
2. muscles that provide movement in the wrist joint, as well as in the midcarpal and carpometacarpal joints: radial and ulnar flexors of the wrist, ulnar extensor of the wrist, palmaris longus muscle;
3. muscles - flexors and extensors of the fingers - superficial flexor of the fingers, deep flexor of the fingers, extensor of the fingers;
4. muscles of individual fingers - long flexor of the thumb, long extensor of the thumb, long muscle that abducts the thumb, extensor of the index finger, extensor of the little finger.

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Anterior forearm muscle group

The anterior muscles of the forearm (flexors) are located in 4 layers. The muscles are considered sequentially from the side of the radius in the direction of the ulna. The first, superficial layer is formed by the following muscles: the brachioradialis muscle, the ulnar flexor of the wrist. The second layer is the superficial flexor of the fingers. The third layer is formed by two muscles: the long flexor of the thumb (from the side of the radius), the deep flexor of the fingers (on the ulnar side). The deepest, fourth layer is represented by the square pronator.

First (superficial) contraction of the forearm muscles

The brachioradialis muscle (m.brachioradialis) has a fleshy origin on the lateral supracondylar crest of the humerus and on the lateral intermuscular septum. At the level of the middle of the forearm, the muscle belly continues into a narrow flat tendon that passes under the tendons of the long abductor muscle and the short extensor of the thumb and attaches to the lateral surface of the distal end of the radius. The brachioradialis muscle limits the cubital fossa on the lateral side.

Function: flexes the forearm at the elbow joint, rotates the radius, places the hand in a position between pronation and supination.

Innervation: radial nerve (CV-CVIII).

Blood supply: radial artery, collateral and recurrent radial arteries.

Pronator teres

(m.pronator teres) - the shortest of the muscles of the superficial layer. At the place of origin it is divided into two unequal parts, the larger of which begins on the medial epicondyle of the humerus, fascia of the forearm, medial intermuscular septum and on the fascial plate separating the muscle from the radial flexor of the wrist. The smaller part originates deeper - on the coronoid process of the ulna. Between these two parts of the round pronator passes the median nerve. The muscle follows in the distal direction and outward, limiting the cubital fossa from the lower medial side. The muscle is attached by a flat tendon in the middle of the lateral surface of the radius.

Function: acting on the proximal and distal radioulnar joints, it rotates the forearm together with the hand towards the elbow (pronation), and also participates in flexion of the forearm at the elbow joint.

Innervation: median nerve (CV-ThI).

Blood supply: brachial, ulnar and radial arteries.

The radial flexor of the wrist (m.flexor carpi radialis) originates on the medial condyle of the humerus, on the fascia and medial intermuscular septum of the humerus. Approximately in the middle of the forearm, the muscle continues into a flat long tendon, which, passing under the flexor retainer (retinaculum flexorum) in a groove on the trapezium bone, is attached to the base of the II (partially III) metacarpal bone.

Function: flexes the wrist, acting together with the radial extensor of the carpi, abducts the hand to the lateral side.

Innervation: median nerve (CV-ThI).

Blood supply: brachial, ulnar and radial arteries.

The palmaris longus muscle (m.palmaris longus) originates on the medial epicondyle of the humerus, on the fascia and adjacent intermuscular septa of the forearm. It has a short muscle belly of a fusiform shape, which in the middle of the forearm passes into a flat long tendon. The tendon passes onto the hand above the flexor retinaculum and is woven into the proximal part of the indian aponeurosis. Sometimes the muscle is absent.

Function: stretches the palmar aponeurosis, simultaneously participating in flexion of the wrist.

Innervation: median nerve (CV-ThI).

Blood supply: radial artery.

Flexor carpi ulnaris

(m.flexor carpi ulnaris) begins with two heads - humeral and ulnar. The humeral head (caput brachiale) originates on the medial epicondyle and on the medial intermuscular septum of the shoulder. The ulnar head (caput ulnare) begins deeper - on the deep leaf of the fascia of the forearm, on the medial edge of the olecranon process and the posterior edge of the ulna.

In the area of the proximal third of the forearm, both heads join into a common belly. Then the muscle goes to the palmar surface of the hand along the medial edge of the forearm and passes into a long tendon, which is attached to the pisiform bone. Part of the tendon bundles continues below, forming the pisiform-hamate ligament, and is attached to the hook of the hamate bone and the pisiform-metacarpal ligament, as well as to the base of the 5th metacarpal bone.

Function: flexes the wrist (together with the flexor carpi radialis); when contracted simultaneously with the extensor carpi ulnaris, it adducts the hand.

Innervation: ulnar nerve (CVII-CVIII).

Blood supply: ulnar artery, superior and inferior collateral ulnar arteries.

The second layer of forearm muscles

The superficial flexor of the fingers (m.flexor digitorum superficialis) begins with two heads - humeroulnar and radial. The heads are connected in the form of a bridge by a tendon stretch, which is crossed in front by the median nerve and ulnar blood vessels.

The humeroulnare head (caput humeroulnare) is larger than the radial head. It originates on the medial epicondyle of the humerus, the fascia of the forearm, the ulnar collateral ligament and on the medial edge of the coronoid process of the ulna. The smaller head, the radial head (caput radiale), originates on the proximal two-thirds of the anterior edge of the radius. In the proximal part of the forearm, both heads join and form a common belly of the muscle, which in the middle of the forearm is divided into 4 parts, which in the distal third of the forearm pass into tendons. These tendons, having passed together with the tendons of the deep flexor of the fingers through the carpal tunnel (under the flexor retinaculum and the palmar aponeurosis), are directed to the palmar surface of the II-V fingers and are attached to the base of the middle phalanges.

At the level of the middle of the proximal phalanx, each tendon of the superficial flexor of the fingers splits into two legs, between which the corresponding tendon of the deep flexor of the fingers passes.

Function: flexes the middle phalanges of the II-V fingers (along with them the fingers themselves), participates in flexion of the hand.

Innervation: median nerve (CV-ThI).

Blood supply: radial and ulnar arteries.

The third layer of forearm muscles

The deep flexor of the fingers (m.flexor digitorum profundus) originates on the proximal two-thirds of the anterior surface of the ulna and on the interosseous membrane of the forearm. Four tendons of the muscle, together with the tendons of the superficial flexor of the fingers, pass through the carpal tunnel. At the level of the proximal phalanges, the tendons of the deep flexor of the fingers pass between the split tendons of the superficial flexor of the fingers and are attached to the bases of the distal phalanges of the II-V fingers.

Function: flexes the distal phalanges of the II-V fingers (along with them the fingers themselves); participates in flexion of the hand at the wrist joint.

Innervation: ulnar and median nerves (CV-ThI).

Blood supply: ulnar and radial arteries.

The long flexor of the pollicis pollicis longus originates on the anterior surface of the radius and the adjacent part of the interosseous membrane of the forearm, extending from the level of the tuberosity of the radius to the upper edge of the quadrate pronator. The tendon of the muscle passes through the carpal canal in a separate synovial sheath. On the palm, it passes between the two heads of the short flexor of the pollicis pollicis and is attached to the base of the distal phalanx of the thumb.

Function: flexes the distal phalanx of the thumb (along with it the finger itself), participates in flexion of the hand.

Innervation: median nerve (CV-ThI).

Blood supply: anterior interosseous artery.

The fourth layer of forearm muscles

The square pronator (m.pronator quadratus) is a flat muscle with transversely oriented fiber bundles. It is located under the tendons of the flexors of the fingers and wrist on the anterior surface of the lower third of the body of the ulna, radius and on the interosseous membrane of the forearm. The muscle begins on the anterior edge and anterior surface of the lower third of the body of the ulna. Passing in the transverse direction, the muscle is attached to the anterior surface of the distal third of the body of the radius.

Function: Pronates the forearm and hand.

Innervation: median nerve (CV-ThI).

Blood supply: anterior interosseous artery.

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Posterior forearm muscle group

The posterior muscles of the forearm are divided into superficial and deep layers. The superficial layer includes 5 muscles: long radial extensor of the wrist, short radial extensor of the wrist, extensor of the fingers, extensor of the little finger, extensor of the carpi ulnaris. The deep layer also includes 5 muscles: supinator, long muscle that abducts the thumb, long extensor of the thumb, extensor of the index finger.

Superficial layer of forearm muscles

The long radial extensor of the wrist (m.extensor carpi radialis longus) begins with muscle bundles on the lateral epicondyle of the humerus and the lateral intermuscular septum of the arm. Here the muscle is directly adjacent to the lateral surface of the capsule of the elbow joint. Distally, along the entire length of the forearm, the muscle occupies the space between the brachioradialis muscle (in front) and the short extensor of the wrist (behind). In the middle of the forearm, the muscle passes into a flat tendon, which, passing under the extensor retainer (retinaculum extensorum), is attached to the base of the second metacarpal bone.

Function: flexes the forearm (slightly), extends the wrist; when contracted simultaneously with the radial flexor of the wrist, abducts the wrist laterally.

Innervation: radial nerve (CV-CVIII).

Blood supply: radial artery, collateral radial and recurrent radial arteries.

The short radial extensor of the wrist (m.extensor carpi radialis brevis) originates on the lateral epicondyle of the humerus, the radial collateral ligament, and the fascia of the forearm. It is attached to the dorsal surface of the base of the third metacarpal bone.

Function: extends the wrist; when contracted simultaneously with the radial flexor of the wrist, abducts the wrist.

Innervation: radial nerve (CV-CVIII).

Blood supply: collateral radial and recurrent radial arteries.

Extensor digitorum

(m.extensor digitorum) is located medial to the radial extensors, originates on the lateral epicondyle of the humerus and on the fascia of the forearm. Near the wrist joint it divides into 4 tendons that pass under the extensor retinaculum in the common synovial sheath and are attached to the back of the II-V fingers, forming tendon extensions. The middle bundles of the tendon extension are attached to the base of the middle phalanx, and the lateral ones - to the distal phalanx. At the level of the metacarpal bones, the tendons of the finger extensors are connected to each other by obliquely oriented fibrous bundles - intertendinous connections (connexus intertendineus).

Function: extends fingers II-V; participates in the extension of the hand at the wrist joint.

Innervation: radial nerve (CV-CVIII).

Blood supply: posterior interosseous artery.

The extensor digiti minimi has a common origin with the extensor digitorum. The thin tendon of this muscle passes under the extensor retinaculum in a separate synovial sheath and is attached to the back of the little finger to the bases of its middle and distal phalanges (the bundles of the muscle tendon are fused with the tendon of the extensor digitorum).

Function: extends the little finger.

Innervation: radial nerve (CV-CVIII).

Blood supply: posterior interosseous artery.

The extensor carpi ulnaris muscle originates from the lateral epicondyle of the humerus, the capsule of the elbow joint, and the fascia of the forearm. It is attached to the base of the 5th metacarpal bone. The tendon of the muscle passes separately in the synovial sheath under the extensor retinaculum, occupying a groove on the posterior surface of the distal end of the ulna.

Function: extends the wrist. Acting together with the ulnar flexor of the wrist, adducts the wrist.

Innervation: radial nerve (CVI-CVIII).

Blood supply: posterior interosseous artery.

Deep layer of forearm muscles

The supinator (m.supinator) is almost completely covered by superficial muscles. The supinator originates on the lateral epicondyle of the humerus, the radial collateral ligament, the annular ligament of the radius, and the supinator crest on the ulna.

The muscle passes obliquely in a lateral direction (covers the radius from behind and from the side) and attaches to the lateral surface of the proximal third of the radius.

Function: rotates the radius bone outward (supinator) together with the hand.

Innervation: radial nerve (CVI-CVIII).

Blood supply: radial, recurrent and interosseous arteries.

The long muscle that abducts the thumb of the hand (m.abductor pollicis longus) originates on the posterior surface of the ulna, the posterior surface of the radius and on the interosseous membrane of the forearm. Following from its origin downwards and laterally, the muscle bends around the outside of the radius with the tendons of the radial extensors of the wrist lying on it. Then the tendon of this muscle passes together with the tendon of the short extensor of the thumb of the hand in one synovial sheath under the lateral part of the extensor retinaculum and is attached to the dorsal surface of the base of the first metacarpal bone.

Function: abducts the thumb; participates in abduction of the wrist.

Innervation: radial nerve (CV-CVIII).

Blood supply: radial artery, posterior interosseous artery.

Extensor pollicis brevis

(m.extensor pollicis brevis) is present only in humans (genetically it is part of the long muscle that abducts the thumb). It starts on the back surface of the radius, on the interosseous membrane of the forearm. The tendon of this muscle passes together with the tendon of the long muscle that abducts the thumb in one synovial sheath under the extensor retinaculum. It is attached to the base of the proximal phalanx of the thumb.

Function: extends the proximal phalanx (along with the finger), abducts the thumb.

Innervation: radial nerve (CV-CVIII).

Blood supply: radial artery, posterior interosseous artery.

The long extensor of the pollicis (m.extensor pollicis longus) originates on the lateral side of the posterior surface of the ulna (within its middle third), on the interosseous membrane of the forearm. The tendon of the long extensor of the pollicis passes under the extensor retinaculum in a separate synovial sheath, in a groove on the posterior surface of the radius. It is attached to the base of the distal phalanx of the thumb.

Function: extends the thumb.

Innervation: radial nerve (CV-CVIII).

Blood supply: radial artery, posterior interosseous artery.

The extensor of the index finger (m.extensor indicis) originates on the posterior surface of the ulna and on the interosseous membrane of the forearm. The tendon of the muscle passes together with the tendons of the extensors of the fingers in the common synovial sheath under the extensor retinaculum. It is attached to the posterior surface of the proximal phalanx of the index finger (the tendon of the muscle is fused with the bundles of the tendons of the extensor of the fingers).

Function: extends the index finger.

Innervation: radial nerve (CV-CVIII).

Blood supply: posterior interosseous artery.

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