Muscles of the posterior compartment of the forearm

Muscle	Proximal attachment	Distal attachment	Innervation*	Main action
Superficial layer
Brachioradialis	Proximal two thirds of supraepicondylar ridge of humerus	Lateral surface of distal end of radius proximal to styloid process	Radial nerve (C5, C6, C7)	Relatively week flexion of forearm, maximal when forearm is in midpronated position
Extensor carpi radialis longus (ECRL)	Lateral supraepicondylar ridge of humerus	Dorsal aspect of base of second metacarpal	Radial nerve (C6, C7)	Extend and abduct hand at the wrist joint; ECRL active during fist clenching
Extensor carpi radialis brevis (ECRB)	Lateral epicondyle of humerus (common extensor origin)	Doral aspect of base of third metacarpal	Deep branch of radial nerve (C7, C8)
Extensor digitorum		Extensor expansions of medial four fingers	Posterior interosseous nerve (C7, C8), continuation of deep branch of radial nerve	Extends medial four fingers primarily at metacarpophalangeal joints, secondarily at interphalangeal joints
Extensor digiti minimi (EDM)		Extensor expansion of fifth finger		Extends fifth finger primarily at metacarpophalangeal joint, secondarily at interphalangeal joint
Extensor carpi ulnaris (ECU)	Lateral epicondyle of humerus; posterior border of ulna via a shared aponeurosis	Dorsal aspect of base of fifth metacarpal		Extends and adducts hand at wrist joint (also active during fist clenching)
Deep layer
Supinator	Lateral epicondyle of humerus; radial collateral and anular ligaments; supinator fossa; crest of ulna	Lateral posterior, and anterior surfaces of proximal third of radius	Deep branch of radial nerve (C7, C8)	Supinates forearm; rotates radius to turn palm anteriorly or superiorly (if elbow is flexed)
Extensor indicis	Posterior surface of distal third of ulna and interosseous membrane	Extensor expansion of second finger	Posterior interosseous nerve (C7, C8), continuation of deep branch of radial nerve	Extends second finger (enabling its independent extension); helps extend hand at wrist
Outcropping muscles of deep layer
Abductor pollicis longus (APL)	Posterior surface of proximal halves of ulna, radius, and interosseous membrane	Base of first metacarpal	Posterior interosseous nerve (C7, C8), continuation of deep branch of radial nerve	Abducts thumb and extends it at carpometacarpal joint
Extensor pollicis longus (EPL)	Posterior surface of middle third of ulna and interosseous membrane	Dorsal aspect of base of distal phalanx of thumb		Extends distal phalanx of thumb at interphalangeal joint; extends metacarpophalangeal and carpometacarpal joints
Extensor pollicis brevis (EPB)	Posterior surface of distal third of radius and interosseous membrane	Dorsal aspect of base of proximal phalanx of thumb		Extends proximal phalanx of thumb at metacarpophalangeal joint; extends carpometacarpal joint

* The spinal cord segmental innervation is indicated (eg, "C7, C8" means that the nerves supplying the extensor carpi radialis brevis are derived from the seventh and eighth cervical segments of the spinal cord). Numbers in boldface (C7) indicate the main segmental innervation. Damage to one or more of the listed spinal cord segments or to the motor nerve roots arising from them results in paralysis of the muscles concerned.

Reproduced with permission from: Moore KL, Dalley AR. Clinically Oriented Anatomy, 5th ed, Lippincott Williams & Wilkins, Philadelphia 2006. Copyright © 2006 Lippincott Williams & Wilkins. www.lww.com.

Graphic 63813 Version 13.0

خرید پکیج

Muscles of the posterior compartment of the forearm