Muscles of the Posterior Forearm

Question 1

What are the muscles in the posterior compartment of the forearm commonly known as?

Answer 1

The extensor muscles

Question 2

What is the general function of the muscles of the posterior compartment of the forearm?

Answer 2

To produce extension at the wrist and fingers

Question 3

What are the extensor muscles innervated by?

Answer 3

The radial nerve

Question 4

What can the muscles of the posterior forearm be divided into?

Answer 4

Two layers, deep and superficial

Question 5

What divides the layers of muscles in the posterior forearm?

Answer 5

A layer of fascia

Question 6

How many muscles are in the superficial layer of the posterior forearm?

Answer 6

6

Question 7

What are the muscles of the superficial layer of the posterior forearm?

Answer 7

Brachioradialis
 Extensor carpi radialis longus
 Extensor carpi radialis brevis
 Extensor digitorum
 Extensor digiti minimi
 Extensor carpi ulnaris

Question 8

What muscles share a common tendinous origin at the lateral epicondyle?

Answer 8

Extensor carpi radialis longus
Extensor digitorum
Extensor digiti minimi
Extensor carpi ulnaris

Question 9

Why is the brachioradialis a paradoxical muscle?

Answer 9

Because its origin and innervation are characteristic of an extensor muscle, but its actually a flexor at the elbow

Question 10

When is the brachioradialis most visible?

Answer 10

When the forearm is half pronated, and flexing elbow against resistance

Question 11

Where are the radial artery and nerve found in the distal forearm?

Answer 11

Sandwiched between the brachioradialis and the deep flexor muscles

Question 12

What is the proximal attachment of the brachioradialis?

Answer 12

Proximal two thirds of the supra-epicondylar ridge of humerus

Question 13

What is the distal attachment of the brachioradialis?

Answer 13

Lateral surface of distal end of radius, proximal to styloid process

Question 14

What is the innervation of the brachioradialis?

Answer 14

Radial nerve (C5, C6, C7)

Question 15

What is the arterial supply of the brachioradialis?

Answer 15

Radial recurrent artery

Question 16

What is the main action of the brachioradialis?

Answer 16

Relatively weak flexion of the forearm, maximal when the forearm is in mid-pronated position

Question 17

Where are the extensor carpi radialis muscles situated?

Answer 17

On the lateral aspect of the posterior forearm

Question 18

What are the extensor carpi radialis muscles able to do due to their position?

Answer 18

Produce abduction as well as extension at the wrist

Question 19

What is the proximal attachment of the extensor carpi radialis longus (ECRL)?

Answer 19

Lateral supra-epicondylar ridge of humerus

Question 20

What is the distal attachment of the ECRL?

Answer 20

Dorsal aspect of base of 2nd metacarpal?

Question 21

What is the innervation of the ECRL?

Answer 21

Radial nerve (C6, C7)

Question 22

What is the arterial supply of the ECRL?

Answer 22

Radial artery

Question 23

What is the proximal attachment of the extensor carpi radialis brevis (ECRB)?

Answer 23

Lateral epicondyle of humerus (common extensor origin)

Question 24

What is the distal attachment of the ECRB?

Answer 24

Dorsal aspect of base of 3rd metacarpal

Question 25

What is the innervation of the ECRB?

Answer 25

Deep branch of radial nerve (C7, C8)

Question 26

What is the arterial supply of the ECRB?

Answer 26

Radial artery

Question 27

What is the main action of the extensor carpi radialis muscles?

Answer 27

Extend and abduct the hand at the wrist joint | ECRL active during fist clenching

Question 28

How is the function of the extensor digitorum tested?

Answer 28

The forearm is pronated, and the fingers extended against resistance

Question 29

What is the proximal attachment of the extensor digitorum?

Answer 29

Lateral epicondyle of humerus (common extensor origin)

Question 30

What is the distal attachment of the extensor digitorum?

Answer 30

Extensor expansions of medial four digits

Question 31

What is the innervation of the extensor digitorum?

Answer 31

Deep branch of radial nerve (C7, C8)

Question 32

What is the arterial supply of the extensor digitorum?

Answer 32

Recurrent interosseous artery  | Posterior interosseous artery

Question 33

What is the action of the extensor digitorum?

Answer 33

Extends medial four digits primarily at metacarpophalangeal joints, secondarily at interphalangeal joints

Question 34

What is true in some people regarding the extensor digiti minimi?

Answer 34

This muscle and the extensor digitorum muscle are fused together

Question 35

Where does the extensor digiti minimi (EDM) lie?

Answer 35

Medially to the extensor digitorum

Question 36

What is the proximal attachment of the EDM?

Answer 36

Lateral epicondyle of humerus (common extensor origin)

Question 37

What is the distal attachment of the EDM?

Answer 37

Extensor expansion of 5th digit

Question 38

What is the innervation of the EDM?

Answer 38

Deep branch of radial nerve (C7, C8)

Question 39

What is the arterial supply of the EDM?

Answer 39

Posterior interosseous artery

Question 40

What is the main action of the EDM?

Answer 40

Extends 5th digit primarily at metacarpophalangeal joint, secondarily at interphalangeal joint

Question 41

Where is the extensor carpi ulnaris (EDU) found?

Answer 41

On the medial aspect of the posterior forearm

Question 42

What is the EDU able to do due to its position?

Answer 42

Produce adduction as well as extension at the wrist

Question 43

What is the proximal attachment of the ECU?

Answer 43

Lateral epicondyle of the humerus  | Posterior border of ulna via a shared aponeurosis

Question 44

What is the distal attachment of the ECU?

Answer 44

Dorsal aspect of base of 5th metacarpal

Question 45

What is the innervation of the ECU?

Answer 45

Deep branch of the radial nerve (C7, C8)

Question 46

What is the arterial supply of the ECU?

Answer 46

Ulnar artery

Question 47

What is the main action of the ECU?

Answer 47

Extends and adducts the hand at the wrist joint  | Active during fist clenching

Question 48

What does lateral epicondylitis refer to?

Answer 48

Inflammation of the periosteum of the lateral epicondyle

Question 49

What is the peak age of onset of lateral epicondylitis?

Answer 49

40-50 years

Question 50

What is lateral epicondylitis caused by?

Answer 50

Repeated use of the superficial extensor muscles, which stains their common tendinous attachment of the lateral epicondyle

Question 51

How many muscles are in the deep compartment of the posterior forearm?

Answer 51

5

Question 52

What muscles are in the deep compartment of the posterior forearm?

Answer 52

``` Supinator  Abductor pollicis longus  Extensor pollicis brevis Extensor pollicis longus  Extensor indicis ```

Question 53

What do the deep muscles of the posterior forearm do?

Answer 53

Act on the thumb and index finger, with the exception of the supinator

Question 54

Where does the supinator lie?

Answer 54

On the floor of the cubital fossa

Question 55

What does the supinator have?

Answer 55

Two heads

Question 56

What passes between the two heads of the supinator?

Answer 56

The deep branch of the radial nerve

Question 57

What is proximal attachment of the supinator?

Answer 57

Lateral epicondyle of the humerus  Radial collateral and anular ligaments Supinator fossa Crest of ulna

Question 58

What is the distal attachment of the supinator?

Answer 58

Lateral, posterior and anterior surfaces of the proximal third of the radius

Question 59

What is the innervation of the supinator?

Answer 59

Deep branch of radial nerve (C7, C8)

Question 60

What is the arterial supply to the supinator?

Answer 60

Recurrent interosseous artery

Question 61

What is the main action of the supinator?

Answer 61

Supinates forearm- rotates radius to turn palm anteriorly or superiorly (if elbow are flexed)

Question 62

Where is the abductor pollicis longus?

Answer 62

Immediately distal to the supinator muscle

Question 63

What does the tendon of the abdutor pollicis longus contribute to?

Answer 63

The lateral border of the anatomical snuffbox

Question 64

What is the proximal attachment of the APL?

Answer 64

Posterior surface of proximal haves of ulna, radius, and interosseous membrane

Question 65

What is the distal attachment of the APL?

Answer 65

Base of 1st metacarpal

Question 66

What is the innervation of the APL?

Answer 66

Posterior interosseous nerve (C7, C8), a continuation of the deep branch of the radial nerve

Question 67

What is the arterial supply of the APL?

Answer 67

Posterior interosseous artery

Question 68

What is the main action of the APL?

Answer 68

Abducts the thumb and extends it at the carpometacarpal joint

Question 69

Where can the extensor pollicis brevis be found?

Answer 69

Medially and deep to the abductor pollicis longus

Question 70

What does the tendon of the EPB contribute to?

Answer 70

The lateral border of the anatomical snuffbox

Question 71

What is the proximal attachment of the EPB?

Answer 71

Posterior surface of the distal third of the radius and interosseous membrane

Question 72

What is the distal attachment of the EPB?

Answer 72

Dorsal aspect of base of proximal phalanx of thumb

Question 73

What is the innervation of the EPB?

Answer 73

Posterior interosseous nerve (C7, C8), a continuation of the deep branch of the radial nerve

Question 74

What is the arterial supply of the EPB?

Answer 74

Posterior interosseous artery

Question 75

What is the main action of the EPB?

Answer 75

Extends proximal phalanx of thumb at metacarpophalgeal joint  Extends carpometacarpal joint

Question 76

How does the extensor pollicis longus different from the EPB?

Answer 76

It has a larger muscle belly

Question 77

Where does the tendon of the EPL travel?

Answer 77

Medially to the dorsal tubercle at the wrist

Question 78

What does the tendon of the EPL act to do?

Answer 78

Uses the dorsal tubercle as a ‘pulley’ to increase the force exerted

Question 79

What does the tendon of the EPL form?

Answer 79

The medial border of the anatomical snuffbox

Question 80

What is the proximal attachment of the EPL?

Answer 80

Posterior surface of middle third of ulna and interosseous membrane

Question 81

What is the distal attachment of the EPL?

Answer 81

Dorsal aspect of the base of distal phalanx

Question 82

What is the innervation of the EPL?

Answer 82

Posterior interosseous nerve (C7, C8), a continuation of the deep branch of the radial nerve

Question 83

What is the arterial supply of the EPL?

Answer 83

Posterior interosseous artery

Question 84

What is the main action of the EPL?

Answer 84

Extends distal phalanx of thumb at interphalangeal joints | Extends metacarpophalangeal and carpometacarpal joints

Question 85

What does the extensor indicis proprius allow?

Answer 85

The index finger to be independent of the other fingers during extension

Question 86

What is the proximal attachment of EIP?

Answer 86

Posterior surface of distal third of ulna and interosseous membrane

Question 87

What is the distal attachment of the EIP?

Answer 87

Extensor expansion of 2nd digit

Question 88

What is the innervation of the EIP?

Answer 88

Posterior interosseous nerve (C7, C8), a continuation of the deep branch of the radial nerve

Question 89

What is the arterial supply of the EIP?

Answer 89

Posterior interosseous artery

Question 90

What is the main action of the EIP?

Answer 90

Extends 2nd digit (enabling independent extension) | Helps extend hand at wrist

Question 91

What is wrist drop a sign of?

Answer 91

Radial nerve injury that has occurred proximal to the elbow

Question 92

What are the common characteristic sites of damage with wrist drop?

Answer 92

Axilla  | Radial groove of humerus

Question 93

What causes wrist drop?

Answer 93

The radial nerve innervates all muscles in the extensor compartment of the forearm. In the event of a radial nerve lesion, these muscles are paralysed. The muscles that flex the wrist are innervated by the median nerve, and thus are unaffected. The tone of the flexor muscles produces unopposed flexion at the wrist joint – wrist drop.