Posterior Forearm Muscles (Forearm Extensors)

The part of the hand between the elbow and wrist is called the forearm or antebrachium. Now, there are several muscles that shape the forearm and help it function. These muscles are divided into the anterior and posterior compartments.

The posterior compartment of the forearm contains the muscles that lie at the posterior aspect of the forearm. There are 11 muscles in the posterior compartment, also called the extensor compartment.

Forearm Extensors with Names, Anatomy, & Functions

These muscles are together referred to as the extensors and are further divided into two groups based on their location: superficial and deep.

Muscle Name	Location Layer	Origin	Insertion	Action	Innervation
1. Extensor digitorum	Superficial	The lateral epicondyle of the humerus via the common extensor tendon	The extensor expansion of 2nd to 5th digits	Extending the index finger to little finger	Posterior interosseous nerve (C7, C8)
2. Extensor digiti minimi	Superficial	Via common extensor tendon	The extensor expansion of the 5th digit	Extending the little finger	Posterior interosseous nerve (C7, C8)
3. Extensor carpi ulnaris	Superficial	Via common extensor tendon; Ulna’s posterior border	Base of the 5th metacrpal	Extending and adducting the wrist	Posterior interosseous nerve (C7, C8)
4. Brachioradialis	Superficial	Lateral supracondylar ridge of humerus	Styloid process of the radius	Flexing the elbow*, pronating the forearm	Radial nerve (C5, C6)
5. Extensor carpi radialis longus	Superficial	Lateral supracondylar ridge of humerus	Base of the 2nd metacarpal	Extending and abducting the wrist	Radial nerve (C6, C7)
6. Extensor carpi radialis brevis	Superficial	Via common extensor tendon	Base of the 3rd metacarpal	Extending and abducting the wrist	Radial nerve (C7, C8)
7. Supinator	Deep	Lateral epicondyle of humerus; supinator crest of ulna	Posterior side of the radius	Supinating the forearm	Posterior interosseous nerve (C7, C8)
8. Extensor indicis	Deep	Posterior surface of distal ulna	The extensor expansion of the 2nd digit	Extending the index finger	Posterior interosseous nerve (C7, C8)
9. Abductor pollicis longus	Deep	Posterior surface of radius and ulna; interosseus membrane	Base of the 1st metacarpal	Extending and abducting the thumb	Posterior interosseous nerve (C7, C8)
10. Extensor pollicis brevis	Deep	Posterior surface of distal radius	Base of 1st distal phalanx	Extending the thumb	Posterior interosseous nerve (C7, C8)
11. Extensor pollicis longus	Deep	Posterior surface of ulna; interosseus membrane	Base of 1st distal phalanx	Extending the thumb	Posterior interosseous nerve (C7, C8)

*The brachioradialis muscle works as a flexor and pronator despite being part of the extensor group of muscles in the forearm. It is the only muscle in this compartment to take part in flexion.

The 3 superficial muscles brachioradialis, extensor carpi radialis longus and extensor carpi radialis brevis constitute the mobile wad of Henry, a lateral compartment within the posterior compartment.

The abductor pollicis longus, extensor pollicis brevis, and extensor pollicis longus tendons on the distal side form the medial and lateral boundaries of the anatomical snuff box, the triangular depression at the base of the thumb.