L5 Posterior (extensor) Compartment Of Arm/forearm

Question 1

What’s the common flexor origin of the four superficial muscles of anterior forearm?

Answer 1

Medial epicondyle (distal humerus)

Question 2

What’s the common extensor origin of superficial muscles of posterior forearm?

Answer 2

Lateral epicondyle of distal humerus

Question 3

Nerve in the posterior compartment of the ARM? It’s main actions?

Answer 3

Radial n

major action Extension of FOREARM
Minor action extension of arm

Question 4

Triceps brachii heads and movements

Answer 4

Long head
Extend arm at shoulder
Extend forearm at elbow

Lateral head
Extend forearm

Medial head (deeper)
   Extend forearm 

Diff origins but common insertion at olecranon process

Question 5

Where does radial n travel in the ARM

Answer 5

Terminal branch of posterior cord

Travels to posterior compartment of arm the triangular interval (teres major, long head triceps and humerus)

Travels deep to lateral head of triceps brachii in radial groove (feature of humerus)

Lies right on humerus (break bone, could damage nerve)

Pierces septum to emerge anteriorly in cubical fossa

Question 6

What does radial n innervate?

Answer 6

Motor innervation to muscles of posterior compartment (C6,C7)

Question 7

Nerve in the posterior compartment of the FOREARM? It’s main actions?

Answer 7

radial n

Main action extension of WRIST and FINGERS
minor action extension of forearm
Supination of forearm

Extensor compartment in forearm is posterior and comes a little bit lateral

Question 8

Muscles of superficial layer of posterior forearm?

Answer 8

Brachioradialis*

Extensor carpi radialis longus *

Extensor carpi radialis brevis

Extensor digitorum

Extensor carpi ulnaris

Extensor digiti minimi

Question 9

Brachioradialis

Answer 9

Is a posterior compartment muscle

Seen better from anterior view

Origin: lateral supercondyl ridge of humerus
Insertion: styloid process of radius

Innervated by radial n

Action: flexes elbow ! (Especially when joint is mid-pronated)

Question 10

What’s different about the extensor carpi radialis longus?

Answer 10

Don’t arise from common extensor tendon (neither does brachioradialis)

Arises inferior from lateral supercondyl ridge

Longer muscle !

Question 11

Insertion of extensor digitorum

Answer 11

At MCP joint each tendon flattens and expends into aponeurosis that wrap around the posterior (dorsum) and sides of the metacarpal and proximal phalanx forming a hood over joint

Distal to MCP joint ED tendons trifurcate
  Central (median) band -insert on poster surface of middle phalanx 
  Lateral bands (2)- insert on posterior surface of distal phalanx 

Hood anchored to palmar ligament at MCP joint (posterior structure anchored to anterior structure)

Question 12

Lumbricals

Answer 12

Simultaneously flexion of MCP joints and extension of IP joints

Tendons of lumbricals insert on the extensor hood

Question 13

Tendons of lumbricals insert on the extensor hood

Answer 13

Extensor digitorum contraction produces extension

Lumbricals
Proximal portion located anterior to MCP contraction produces FELXION
Distal portion located posterior to PIP, DIP contraction produces EXTENSION

Question 14

Deep layer of muscles of posterior forearm

Answer 14

Supinator

Extensor indicis

Abductor pollicis longus

Extensor pollicis brevis

Extensor pollicis longus

Question 15

Supination is stronger than

Answer 15

Pronation

And is stronger in flexion than in extension

Question 16

Supinator is active

Answer 16

Every time we supinate

Supination by biceps brachii occurs when elbow flexion is also needed or when speed/strength needed

Question 17

Anatomical snuffbox has

Answer 17

Triangular depression on radial aspect of the wrist

Anterior side: extensor pollicis brevis, abductor pollicis longus

Posterior side: extensor pollicis longus

Floor: scaphoid and trapezium

Radial a. Passes through (where you get radial pulse)

Question 18

Scaphoid fracture is

Answer 18

The most common carpal injury

Falling on palm when hand is extended and abducted results in extreme extension and compression of radial side of hand

Question 19

Where does radial n travel in the FOREARM

Answer 19

Deep radial n provides motor innervation (C7)
Passes through supinator

Superficial radial n. is purely sensory (C7)
branches off at cubical fossa more anterior than deep radial n.

Question 20

Myotomes of UE

Answer 20

Shoulder -C5,6

Arm- C5,6,7

Forearm- C8

Hand - T1

Question 21

All wrist muscles have dual actions at the joint

Answer 21

Pure movement requires simultaneous contraction of more than one muscle

I.e. flexion: FCU- adducts , flexes hand
FCR abducts, flexes hand
Abduction and adduction cancel each other out

Expect palmaris longus