Extensor digitorum muscle
Extensor digitorum is a long muscle located in the posterior compartment of the forearm. Together with extensor carpi ulnaris and extensor digiti minimi, it comprises the group of superficial extensors of the forearm. These muscles can be easily palpated in the lateral aspect of the posterior forearm, especially during the extension of hand when they are contracted.
Extensor digitorum runs from the lateral epicondyle of humerus to the medial four phalanges of the hand. In this way, it generates the pull for the extension of the four medial fingers in their metacarpophalangeal and both interphalangeal joints. Extensor digitorum also participates in the extension of the wrist.
|Origin||Lateral epicondyle of humerus (common extensor tendon)|
|Insertion||Extensor expansions of digits 2-5|
|Action||Metacarpophalangeal / Interphalangeal joints 2-5: Finger extension|
|Innervation||Posterior interosseous nerve (C7, C8)|
|Blood supply||Posterior interosseous artery, radial recurrent artery, anterior interosseous artery|
In this article, we will discuss the anatomy and function of extensor digitorum muscle.
Origin and insertion
Extensor digitorum is a superficial muscle of the posterior compartment of the forearm. Like the majority of the muscles in this compartment, it originates via common extensor tendon that arises from the lateral epicondyle of humerus. This tendon serves as a proximal attachment for extensor digiti minimi, extensor carpi radialis brevis and extensor carpi ulnaris muscles.
From its origin, the muscle descends superficially down the posterior aspect of the forearm. At the approximately 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. Some of the tendons are connected by the oblique intertendinous connections that are variable among individuals.
The tendons insert onto the dorsal surface of digits 2-5, respectively. Each tendon attaches to its respective digit via extensor expansion (extensor hood). This is a triangular aponeurotic expansion formed by the inserting tendons of digital extensors, lumbricals and interossei muscles. It covers the dorsal surfaces of digits 2-5, extending from the metacarpophalangeal joint all the way to the proximal interphalangeal joint of each digit. When it reaches the distal end of proximal phalanx, each extensor hood divides into three separate slips; the central part and two collateral (lateral) parts. The central part inserts onto the dorsal aspect of the base of the middle phalanx, while the two collateral parts merge with the intrinsic muscles of the hand to form a conjoint tendon that inserts onto the base of distal phalanx.
Being located superficial to abductor pollicis longus and extensor pollicis longus muscles, extensor digitorum is the most superficial muscle of the posterior forearm. These three muscles enclose a tunnel through which posterior interosseous artery and nerve pass.
In the forearm, extensor digitorum is situated medial to extensor carpi radialis brevis muscle and lateral to extensor digiti minimi and extensor carpi ulnaris muscles.
Deep to extensor retinaculum, its tendons are placed between the tendons of extensor digiti minimi on its medial side, and extensor pollicis longus on its lateral side. Along with extensor indicis, the tendons of extensor digitorum occupy the fourth extensor (dorsal) compartment. In the dorsum of the hand the tendons of extensor digitorum run superficial to dorsal interossei muscles.
Extensor digitorum is innervated by posterior interosseous nerve which is a continuation of a deep branch of radial nerve (root value C7 and C8).
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Extensor digitorum is vascularized by the branches of three different arteries;
- posterior interosseous artery
- radial recurrent artery
- anterior interosseous artery
As its name suggests, the main function of extensor digitorum is the extension of four medial fingers in metacarpophalangeal and proximal and distal interphalangeal joints. It's important to highlight that the action of this single muscle opposes the actions of two flexors of the fingers; flexor digitorum superficialis and flexor digitorum profundus. This muscle participates in the anatomy of the grip as it contributes to the opening of the hand and letting go of an object. As it crosses the wrist, the contraction of extensor digitorum participates in the extension of this joint.