Deep muscles of the posterior forearm

Question 1

What are the deep muscles of the posterior forearm? (5)

Answer 1

• Supinator
• Abductor pollicis longus
• Extensor pollicis brevis
• Extensor pollicis longus
• Extensor indicis

Question 2

Supinator

Answer 2

O: Common extensor origin on lateral epicondyle of the humerus (humeral head) and the supinator crest on proximal shaft of the ulna (ulnar head)

I: Proximal radial (lateral) surface of the radius extending to pronator teres

I: Deep branch of redial nerve

A: Supination of the forearm (absence of resistance)
(forms the floor of the cubital fossa)

Question 3

Abductor Pollicis Longus

Answer 3

O: Interosseous membrane and adjacent posterior surfaces of the radius and ulna

I: Radial/lateral side of the base of the first metacarpal

I: Radially abducts the thumb and assists in extension of the carpometacaroal joint

A: Posterior interosseous branch of the radial nerve

Question 4

Extensor Pollicis Brevis

Answer 4

O: Posterior surface of the radius and interosseous membrane

I: Base of the proximal phalanx of the thumb

I: Posterior interosseous branch of the radial nerve

A: Extends the metacarpophalangeal and carpometacarpal joints of the thumb

Question 5

Extensor Indicis

Answer 5

O: Posterior surface of the ulna and interosseous membrance (distal to the origin of extensor pollicis longus)

I: Extensor hood of the index finger on the ulnar/medial side of the tendon of extensor digitorum

I: Posterior interosseous branch of the radial nerve

A: Extends the index finger

Question 6

Extensor Pollicis Longus

Answer 6

O: Middle third of the posterior surface of the ulna and interosseous membrane

I: Distal phalanx of the thumb

I: Posterior interosseous branch of the radial nerve

A: Extends all of the joints of the thumb (carpometacarpal, metacarpophalangeal, interphalangeal)