The extensor digitorum muscle (also known as extensor digitorum communis) is a

muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of mus ...

of the posterior forearm present in humans and other animals. It extends the medial four digits of the hand. Extensor digitorum is innervated by the posterior interosseous nerve, which is a branch of the radial nerve.

Structure

The extensor digitorum muscle arises from the lateral epicondyle of the humerus, by the common tendon; from the intermuscular septa between it and the adjacent muscles, and from the antebrachial fascia. It divides below into four tendons, which pass, together with that of the

extensor indicis proprius In human anatomy, the extensor indicis roprius'' is a narrow, elongated skeletal muscle in the deep layer of the dorsal forearm, placed medial to, and parallel with, the extensor pollicis longus. Its tendon goes to the index finger, which it exte ...

, through a separate compartment of the dorsal carpal ligament, within a mucous sheath. The tendons then diverge on the back of the hand, and are inserted into the middle and distal

phalanges The phalanges (singular: ''phalanx'' ) are digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges. The phalanges are classed as long bones. ...

of the fingers in the following manner.''

Gray's anatomy ''Gray's Anatomy'' is a reference book of human anatomy written by Henry Gray, illustrated by Henry Vandyke Carter, and first published in London in 1858. It has gone through multiple revised editions and the current edition, the 42nd (Octo ...

'' (1918), see infobox Opposite the metacarpophalangeal articulation each tendon is bound by

fasciculi Fascicle or ''fasciculus'' may refer to: Anatomy and histology * Muscle fascicle, a bundle of skeletal muscle fibers * Nerve fascicle, a bundle of axons (nerve fibers) ** Superior longitudinal fasciculus *** Arcuate fasciculus ** Gracile fasci ...

to the collateral ligaments and serves as the dorsal ligament of this joint; after having crossed the joint, it spreads out into a broad aponeurosis, which covers the dorsal surface of the first

phalanx The phalanx ( grc, φάλαγξ; plural phalanxes or phalanges, , ) was a rectangular mass military formation, usually composed entirely of heavy infantry armed with spears, pikes, sarissas, or similar pole weapons. The term is particularly ...

and is reinforced, in this situation, by the tendons of the

interossei {{short description, Muscles between certain bones Interossei refer to muscles between certain bones. There are many interossei in a human body. Specific interossei include: On the hands * Dorsal interossei muscles of the hand * Palmar interosse ...

and lumbricalis. Opposite the first interphalangeal joint this aponeurosis divides into three slips; an intermediate and two collateral: the former is inserted into the base of the second phalanx; and the two collateral, which are continued onward along the sides of the second phalanx, unite by their contiguous margins, and are inserted into the dorsal surface of the last phalanx. As the tendons cross the interphalangeal joints, they furnish them with dorsal ligaments. The tendon to the index finger is accompanied by the tendon of

extensor indicis In human anatomy, the extensor indicis roprius'' is a narrow, elongated skeletal muscle in the deep layer of the dorsal forearm, placed medial to, and parallel with, the extensor pollicis longus. Its tendon goes to the index finger, which it exte ...

, which lies on its

ulna The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...

r side. On the back of the hand, the tendons to the middle, ring, and little fingers are connected by two obliquely placed bands, one from the third tendon passing inferior and laterally to the second tendon, and the other passing from the same tendon inferior and medially to the fourth. The extensor tendons are connected to the second by a thin transverse band, known as the

juncturae tendinum In human anatomy, juncturae tendinum or ''connexus intertendinei'' refers to the connective tissues that link the tendons of the extensor digitorum communis, and sometimes, to the tendon of the extensor digiti minimi. Juncturae tendinum are locat ...

; they serve to maintain the central alignment of the extensor tendons over the metacarpal head, thus increasing the available

lever A lever is a simple machine consisting of a beam or rigid rod pivoted at a fixed hinge, or '' fulcrum''. A lever is a rigid body capable of rotating on a point on itself. On the basis of the locations of fulcrum, load and effort, the lever is d ...

age. Injuries (such as by an external flexion force during active extension) may allow the tendon to dislocate into the intermetacarpal space; the extensor tendon then acts as a flexor and the finger may no longer be actively extended. This may be corrected surgically by using a slip of the extensor tendon to replace the damaged ligamentous band.

Function

The extensor digitorum muscle extends the phalanges, then the wrist, and finally the elbow. It tends to separate the fingers as it extends them. In the fingers, the extensor digitorum acts principally on the proximal phalanges, acting to extend the

metacarpophalangeal joint The metacarpophalangeal joints (MCP) are situated between the metacarpal bones and the proximal phalanges of the fingers. These joints are of the condyloid kind, formed by the reception of the rounded heads of the metacarpal bones into shallow ...

. Extension of the proximal and distal interphalangeal joints, however, is mediated predominantly by the

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal c ...

and palmar interossei and

lumbricals of the hand The lumbricals are intrinsic muscles of the hand that flex the metacarpophalangeal joints, and extend the interphalangeal joints. p. 97 The lumbrical muscles of the foot also have a similar action, though they are of less clinical concern. S ...

Additional images

References

{{Authority control Muscles of the upper limb

Structure

Function

Additional images

See also

References