Posterior Arm and Forearm

Question 1

Posterior compartment of the arm innervation

Answer 1

Posterior division of brachial plexus – radial n (C5-8) and axillary n (C5-8)

Question 2

Radial nerve branches and innervations

Answer 2

• -Superficial (cutaneous innervation to dorsum of hand)
• -Deep (motor innervation to extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, and supinator)
• -Posterior interosseous (ABLE muscles)

Question 3

Posterior compartment of the arm (general action, innervation)

Answer 3

All are EXTENSORS, all are innervated by RADIAL N

Question 4

Triceps brachii: action

Answer 4

Long head: goes to shoulder to extend and adduct shoulder

All heads: extend elbow

Question 5

Triceps brachii: attachments

Answer 5

Proximal attachments – long head = infraglenoid tubercle, lateral head = posterior humerus, medial head = deep/posterior humerus
Distal attachment – olecranon process

Question 6

Anconeus: action

Answer 6

Extends and stabilizes the elbow

Question 7

Anconeus: attachments

Answer 7

Proximal attachment – lateral epicondyle of humerus

Distal attachment – posterior ulna

Question 8

Posterior compartment of the forearm (general action, innervation)

Answer 8

Most are extensors of wrists or digits EXCEPT brachioradialis (flexor) and supinator, all are innervated by RADIAL N

Question 9

General origin of all posterior compartment forearm muscles

Answer 9

Originate from lateral epicondyle of humerus or posterior surface of forearm – distal attachment determines action

Question 10

Brachioradialis: insertion

Answer 10

Process of radius

Question 11

Brachioradialis: action

Answer 11

Flexes elbow, no action on wrist (can help out biceps and musculocutaneous n loss)

Question 12

Extensor carpi radialis longus: insertion

Answer 12

Base of metacarpal II

Question 13

Extensor carpi radialis longus: action

Answer 13

Extends and abducts wrist

Question 14

Extensor carpi radialis brevis: insertion

Answer 14

Base of metacarpal III

Question 15

Extensor carpi radialis brevis: action

Answer 15

Extends and abducts wrist

Question 16

Extensor carpi radialis brevis: innervation

Answer 16

Deep branch of radial n

Question 17

Extensor carpi ulnaris: insertion

Answer 17

Base of metacarpal V

Question 18

Extensor carpi ulnaris: innervation

Answer 18

Deep branch of radial n

Question 19

Extensor carpi ulnaris: action

Answer 19

Extends and adducts wrist

Question 20

Extensor digitorum: insertion

Answer 20

Extensor expansion of digits 2-5

Question 21

Extensor digitorum: innervation

Answer 21

Deep branch of radial n

Question 22

Extensor digitorum: action

Answer 22

Extends digits 2-5 at all joints and assists in extending wrist

Question 23

Extensor digiti minimi: insertion

Answer 23

Extensor expansion of digit 5

Question 24

Extensor digiti minimi: action

Answer 24

Extends digit 5 at all joints and assists in extending wrist

Question 25

Extensor expansions

Answer 25

Sheets of connective tissue that join up with extensor tendons that serve as origins for other muscles

Question 26

Supinator: insertion

Answer 26

Olecranon process, proximo-lateral radius

Question 27

Abductor pollicis longus: attachments

Answer 27

Posterior ulna, radius, and interosseous membrane to base of MC I

Question 28

Innervation of ABLE muscles

Answer 28

Posterior interosseous n

Question 29

Difference between action of extensor pollicis brevis and longus

Answer 29

Brevis only extends pollex at MCP joint while longus extends at all joints

Question 30

Anatomical snuff box (contents, borders)

Answer 30

``` Contents = radial artery, scaphoid bone, superficial branch of radial n Borders = tendon of extensor pollicis longus and extensor pollicis brevis/abductor pollicis longus ```

Question 31

Extensor indicis: action

Answer 31

Extends digit 2 at all joints, extends wrist

Question 32

Extensor indicis: attachments

Answer 32

Origin: posterior ulna and interosseous membrane Insertion: extensor expansion of digit 2

Question 33

Radial nerve injury

Answer 33

Caused by compression of radial nerve at any point -- if on axilla or proximal arm leads to weakness of triceps, inability to extend wrist ("wrist drop"), paresthesia, numbness over dorsum of hand and posterior forearm -- ex. crutch palsy (using crutches incorrectly)

Question 34

Triangular interval borders

Answer 34

Lateral: lateral head of triceps Medial: long head of triceps Superior: teres major

Question 35

Triangular interval contents

Answer 35

Radial nerve, profunda brachii artery

Question 36

Midshaft humeral fracture

Answer 36

Damages the contents of the triangular interval, causes wrist drop

Question 37

Handcuff palsy

Answer 37

Paresthesia or numbness over dorsum of the hand, between metacarpal I and II (superficial branch of radial nerve)