Athena Vale
The human hand is a complex structure with 30+ muscles, each with its own unique function. One of the most important functions of the hand is the ability to extend the fingers, which is primarily facilitated by the extensor digitorum muscle. This muscle is located in the forearm and is responsible for extending the middle, ring, and little fingers, also known as the medial four fingers. It works in conjunction with other muscles and tendons to allow for a wide range of finger movements and hand grips.
| Characteristics | Values |
|---|---|
| Muscle name | Extensor digitorum muscle (also known as extensor digitorum communis) |
| Muscle group | Extrinsic extensor muscles of the hand |
| Muscle type | Skeletal |
| Muscle location | Posterior compartment of the forearm |
| Muscle function | Extension of the medial four fingers in the metacarpophalangeal and proximal and distal interphalangeal joints |
| Innervation | Posterior interosseous nerve, a branch of the radial nerve |
| Blood supply | Branches of three different arteries: anterior and posterior interosseous arteries (branches of the common interosseus artery, which arises from the ulnar artery) and the radial recurrent artery (a branch of the radial artery) |
| Tendon | Four tendons that pass through a separate compartment of the dorsal carpal ligament within a mucous sheath |
| Ligament | Dorsal ligaments of the interphalangeal joints |
| Surgical correction | In case of tendon dislocation, a slip of the extensor tendon can be used to replace the damaged ligamentous band |
| Associated muscles | Extensor carpi ulnaris, extensor digiti minimi, extensor carpi radialis longus, extensor carpi radialis brevis, and brachioradialis |
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What You'll Learn
Extensor digitorum muscle
Extensor digitorum is a long muscle located in the posterior compartment of the forearm. It is one of the extrinsic muscles of the hand. Extensor digitorum is also known as extensor digitorum communis (EDC). It is a muscle of the superficial layer of the posterior forearm. Extensor digitorum is the most superficial muscle of the posterior forearm. It is located superficial to abductor pollicis longus and extensor pollicis longus muscles.
Extensor digitorum is vascularized by the branches of three different arteries. The anterior and posterior interosseous arteries are the branches of the common interosseus artery that arises from the ulnar artery. The radial recurrent artery is a branch of the radial artery. Extensor digitorum is innervated by the posterior interosseous nerve, which is a branch of the radial nerve.
Extensor digitorum arises from the lateral epicondyle of the humerus, by the common tendon. It descends superficially down the posterior aspect of the forearm. At the distal third of the forearm, the muscle belly ends in four tendons that enter the dorsum of the hand, passing deep to extensor retinaculum. In the hand, the tendons diverge towards the medial four fingers. The tendons insert into the middle and distal phalanges of the fingers.
Extensor digitorum acts to extend the four medial fingers in their metacarpophalangeal and both interphalangeal joints. It also participates in the extension of the wrist and elbow. It tends to separate the fingers as it extends them. It contributes to the opening of the hand and letting go of an object.
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Extensor indicis muscle
Extensor indicis is a narrow, elongated muscle found in the posterior compartment of the forearm. It is one of the deep extensors of the forearm, along with the supinator, abductor pollicis longus, extensor pollicis longus, and extensor pollicis brevis muscles. The index finger has its own separate extensor muscle, allowing it to extend independently from other fingers.
Extensor indicis receives its nerve supply from the posterior interosseous nerve, a branch of the radial nerve derived from spinal roots C7 and C8. The skin overlying the muscle is supplied by the same nerve, with fibres stemming from the spinal roots C6 and C7. The muscle receives arterial blood supply from the posterior interosseous branch of the ulnar artery and perforating branches of the anterior interosseous artery.
Extensor indicis acts at the metacarpophalangeal and interphalangeal joints to extend the index finger. It originates mainly from the ulna, arising from the posterior two-thirds of its distal surface, distal to the extensor pollicis longus muscle. Some fibres also stem from the adjacent interosseous membrane. It extends inferiorly and narrows into a tendon that passes deep to the extensor retinaculum.
The extensor indicis tendon lies in the fourth dorsal (extensor) compartment of the wrist, sharing this compartment with the tendons of the extensor digitorum muscle. Opposite the head of the second metacarpal bone, it joins the ulnar side of the tendon of the extensor digitorum, which belongs to the index finger. The extensor indicis tendon runs and inserts on the ulnar side of the tendon of the common extensor digitorum, similar to the extensor digiti minimi (the extensor of the little finger).
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Lumbrical muscles
The lumbrical muscles are a set of four intrinsic hand muscles that are attached to the flexor digitorum profundus (FDP) tendons proximally and the digits' extensor expansions distally. They are cylindrical and worm-like, resembling earthworms belonging to the genus Lumbricus. They are located deep in the palm and are essential for the fingers' precision grip and fine motor control.
Each finger is attached to two lumbricals, except for the thumb, which is associated only with the first lumbrical muscle. The first and second lumbricals (the most radial two) are innervated by the median nerve, while the third and fourth lumbricals (the most ulnar two) are innervated by the deep branch of the ulnar nerve. This is the most common innervation pattern of the lumbricals, occurring in 50-60% of individuals. However, variations exist, with 20-30% of individuals having different innervation patterns.
The lumbrical muscles flex the metacarpophalangeal (MCP) joints and extend the proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints. By coordinating with other hand muscles, the lumbricals help control the fine and delicate movements of the fingers. They are also involved in sensory feedback, which is important for precision pinch movements and precise manipulation of objects.
The lumbrical muscles are relevant in carpal tunnel syndrome and can be damaged in crush injuries to the hand. They have a high number of muscle spindles, indicating that they play a role in proprioception and may be important for proprioceptive monitoring of the fingers.
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Interossei muscles
The interossei muscles are muscles found near the metacarpal bones that help to control the fingers. They are further divided into two types: dorsal interossei and palmar interossei.
Dorsal Interossei
The dorsal interossei muscles are short, bipennate, intrinsic muscles of the hand. They are found on the dorsal aspect of the hand occupying the space between the metacarpal bones, along with the palmar interossei muscles. The dorsal interossei consist of four short muscles that attach to the adjacent sides of metacarpals 1-4. Their function is to abduct the digits 2-4, as well as to assist in flexion of these fingers at the metacarpophalangeal (MCP) joints and in extension at the interphalangeal (IP) joints. The first dorsal interosseous can be easily felt in the web between the thumb and index finger. The main function of the dorsal interossei is to abduct the fingers 2-4 in a longitudinal axis, moving them away from each other.
Palmar Interossei
The palmar interossei adduct the digits towards the 3rd digit (towards the axial line) and are unipennate. The axial line goes down the middle of the 3rd digit, towards the palm of the hand.
Both sets of muscles are innervated by the deep branch of the ulnar nerve.
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Abductor pollicis longus muscle
The abductor pollicis longus muscle (APL) is one of the five deep extensors in the forearm, along with the supinator, extensor pollicis brevis, extensor pollicis longus, and extensor indicis. It is also one of the extrinsic muscles of the hand, originating in the forearm.
The abductor pollicis longus is responsible for facilitating movement and stabilization of the thumb. Its tendon is present in the first extensor compartment of the wrist. The muscle belly of the abductor pollicis longus lies in the distal half of the posterior forearm, and its tendon is located lateral to the tendon of the extensor pollicis brevis.
The abductor pollicis longus abducts and extends the thumb at the carpometacarpal joint, moving the thumb anteriorly. It also assists in rotating the thumb and abducting the wrist (radial deviation). Acting together with the abductor pollicis brevis, the abductor pollicis longus pulls the thumb away from the palm, helping to fully extend the thumb at the metacarpophalangeal joint. This action is important for loosening the hand grip, such as when letting go of objects.
The abductor pollicis longus is innervated by the posterior interosseous nerve, which is a continuation of the deep branch of the radial nerve after it passes through the supinator muscle. The muscle is supplied by the posterior interosseous artery, with the proximal part supplied by its lateral branch, and the distal part vascularised by a perforating branch of the anterior interosseous artery.
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Frequently asked questions
The extensor digitorum muscle, also known as extensor digitorum communis, extends the medial four digits of the hand. The extensor carpi radialis longus, extensor carpi radialis brevis, and extensor carpi ulnaris muscles extend the hand at the wrist. The abductor digiti minimi, flexor digiti minimi, and opponens digiti minimi work together to provide a wide range of motion to the little finger.
The extensor digitorum muscle is a long muscle located in the posterior compartment of the forearm. It extends the four medial fingers in their metacarpophalangeal and interphalangeal joints. It is innervated by the posterior interosseous nerve, a branch of the radial nerve.
The main function of the extensor digitorum muscle is to extend the four medial fingers, allowing them to straighten. It also participates in the extension of the wrist and elbow. Additionally, it contributes to the opening of the hand and the grip by helping to let go of objects.
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