Extensors of the Forearm Flashcards by John Jonah Jameson Jr.

What are the layers of the extensors of the forearm?

Superficial layer
Deep layer

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What are the groups of muscles of the superficial layer?

Lateral group:
* Brachioradialis (1)
* Extensor carpi radialis longus (2)
* Extensor carpi radialis brevis (3)
* Extensor digitorum (4)
* Extensor digiti minimi (5)

Medial group:
* Extensor carpi ulnaris (6)
* Anconeus (7)

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Origin of the brachioradialis

Lateral group

Upper part of lateral supra-condylar ridge of humerus

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Insertion of the brachioradialis

Base of styloid process of radius

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Action of the brachioradialis

Accessory flexor of elbow joint when forearm is mid-pronated

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Nerve supply of the brachioradialis

Radial nerve

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Origin of the extensor carpi radialis longus

Lateral group

Lower part of lateral supra-condylar ridge of humerus

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Insertion of the extensor carpi radialis longus

Dorsal surface of base of metacarpal 2

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Action of extensor carpi radialis longus

Extends and abducts the wrist

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Nerve supply of the extensor carpi radialis longus

Radial nerve

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Origin of extensor carpi radialis brevis

Lateral group

Lateral epicondyle of humerus

The lateral epicondyle of the humerus in the common extensor origin

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Insertion of the extensor carpi radialis brevis

Dorsal surface of base of metacarpal 3

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Action of the extensor carpi radialis brevis

Extends and abducts the wrist

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Nerve supply of the extensor carpi radialis brevis

Deep branch of the radial nerve

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Origin of the extensor digitorum

Lateral group

Lateral epicondyle of humerus

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Insertion of extensor digitorum

Four tendons, into the dorsal aspects of the bases of the middle and distal phalanges of the medial 4 fingers

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Action of the flexor digitorum

Extends the inter-phalangeal joints of the medial 4 fingers
Extends the metacapo-phalangeal joints
Extends the wrist

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Nerve supply of the extensor digitorum

Posterior interosseous branch of radial nerve

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Origin of the extensor digiti minimi

Lateral group

Lateral epicondyle of humerus

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Insertion of extensor digiti minimi

Extensor expansion of little finger

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Action of extensor digiti minimi

Extends the little finger

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Nerve supply of the extensor digiti minimi

Posterior interosseous nerve

Origin of extensor carpi ulnaris

(Medial group)

Lateral epicondyle of humerus and posterior border of ulna

Insertion of extensor carpi ulnaris

Base of metacarpal 5

Action of extensor carpi ulnaris

Extends and adducts the wrist

Nerve supply of extensor carpi ulnaris

Posterior interosseous nerve

Origin of anconeous | (Medial group)

Posterior surface of lateral epicondyle of humerus

Insertion of the anconeous

Olecranon and upper posterior surface of ulna

Action of anconeous

* Extensor of the elbow joint * Abduction of ulna in pronation

Nerve supply of anconeous

Radial nerve

Deep layer muscles in extensor compartment of the forearm

* Supinator * Abductor pollicis longus * Extensor pollicis longus * Extensor pollicis brevis * Extensor indicis

Origin of supinator

Lateral epicondyle of humerus & supinator crest of the ulna

Insertion of supinator

Lateral surface of radius above the oblique line

Action of supinator

Supination

Nerve supply of supinator

Posterior interosseous nerve

Origin of abductor pollicis longus

Upper part of posterior surfaces of ulna and radius

Insertion of abductor pollicis longus

Lateral side of base of metacarpal 1

Action of abductor pollicis longus

Abducts carpometacarpal joint of thumb

Nerve supply of abductor pollicis longus

Posterior interosseous nerve

Origin of extensor pollicis brevis

Middle of the posterior surface of radius

Insertion of extensor pollicis brevis

Dorsal surface of base of proximal phalanx of the thumb

Action of extensor pollicis brevis

Extends metacarpo-phalangeal joint of the thumb; also extend the carpo-metacarpal joint of the thumb

Nerve supply of extensor pollicis brevis

Posterior interosseous nerve

Origin of extensor pollicis longus

Middle of the posterior surface of ulna

Insertion of extensor pollicis longus

Dorsal surface of base of distal phalanx of thumb

Action of extensor pollicis longus

Extends inter-phalangeal joint of the thumb Extends metacarpo-phalangeal joints of the thumb Extend carpo-metacarpal joints of the thumb

Nerve supply of extensor pollicis longus

Posterior interosseous nerve

Origin of the extensor inidicis

Lower part of posterior surace of ulna

Insertion of extensor inidicis

Extensor expansion of index finger

Action of extensor indicis

Extends index finger

Nerve supply of extensor indicis

Posterior interosseous nerve

What is the extensor retinaculum?

Thickening of the deep fascia on the dorsum of the wrist

What is the function of the extensor retinaculum?

It holds the long extensor tendons in position

What is the attachment of the extensor retinaculum?

Medially to the triquetrum & pisiform bones and laterally to the lower part of the anterior border of radius