Lecture 13: Forearm extensor compartment

Question 1

What are the 7 superficial extensor muscles of the forearm from front of the forearm to the medial end of the back of the forearm and the two places of their origin

Answer 1

Brachioradialis, extensor carpi radialis longus, = lateral surpracondylar ridge of the humerus
extensor carpi radialis brevis, Extensor digitorum, Extensor digiti minimi, extensor carpi ulnaris + anconeus = common extensor tendon from the lateral epicondyle

Question 2

What superficial muscle forms the boundary between the flexor and extensor compartment

Answer 2

brachioradialis

Question 3

What is the origin, insertion and movement of the brachioradialis

Answer 3

origin: lateral supracondylar ridge of the humerus
insertion: base of the radial styloid process
movement : flexes the elbow

Question 4

What are the extensor muscles that act on the wrist and what are their origin and insertions

Answer 4

Extensor carpi:
Radialis longus origin is supracondylar ridge and it inserts on the base of the 2nd metacarpal
Radialis brevis origin is common extensor tendon and it inserts on the base of 3rd metacarpal
Ulnaris origin has same origin + aponeurotic attachement to the posterior border of the ulna. inserts on 5th metacarpal

Question 5

What is the origin, insertion and movement of anconeous

Answer 5

Origin is common extensor tendon,
insertion is on the superior posterior surface of the ulna
Movement is to extend the elbow

Question 6

How do the 5 carpi muscles (FCU, FCR, ECRL, ECRB and ECU) interact together to give the flexion, abduction, extension and adduction of the wrist

Answer 6

The flexor muscles are on the front with the extensors on the back. The muscles on the radius are on the lateral side so will help abduction whereas the muscles on the ulna will help with adduction. They form a rectangle. In order to only have action (ie pure flexion) the two/more muscles on that direction have to work together because one muscle by itself produces a combination of both flex/ext and abd/add.

Question 7

What are the 5 deep extensor muscles of the forearm from superior to inferior

Answer 7

Supinator (which has a superficial and deep head) , Abductor pollicis longus, extensor pollicis longus, extensor pollicis brevis and extensor indicis

Question 8

What are the sup and deep extensor muscles that extend the fingers. What is their origins and common insertion

Answer 8

Sup: with common origin of common flexor tendon extensor digitorum and Extensor digiti minimi and
Deep: Extensor indicis with origin at posterior surface of ulna and interosseous membrane.
the common insertion is into the dorsal digital expansion hood of the specific fingers that it refers to

Question 9

What are the extensor muscles that act on the thumb and what are their origin and insertions

Answer 9

Abductor pollicis longus which originates from posterior surface of ulna and the interosseous membrane and inserts on the base of the first metacarpal

Extensor pollicis brevis which originates from interosseous membrane and posterior surface of the radius and inserts on the base of the proximal phalanx

Extensor pollicis longus which originates from the lower posterior surface of the ulna and the interosseous membrane and inserts on the base of the distal phalanx

Question 10

What is the origin, insertion and movement of Supinator. What muscle helps supinator

Answer 10

Origin has two heads and inserts onto the antero lateral aspect of the radius to remove the forearm from pronation. This is helped by biceps brachii which inserts onto the radial tuberosity.

Question 11

All the extensor tendons go under what structure

Answer 11

extensor retinaculum

Question 12

Which tendon is on top of which: sup ECRL & B or deep APL, EPB and EPL

Answer 12

The tendons of deep APL, EPB and EPL are on top.

Question 13

What are the two outcropping muscles

Answer 13

Abductor pollicis longus and Extensor pollicis brevis

Question 14

What two forearm muscles work to pronate the arm

Answer 14

pronator teres and pronator quadratus

Question 15

What does insertion into the dorsal digital extension hood mean - how many bands eventually insert and where

Answer 15

There is a centre band inserting into the base of the proximal phalanx and 2 lateral bands going further to insert on the base of the distal phalanx

Question 16

What nerve innervates motors the extensor compartment

Answer 16

Radial nerve.
Starts as radial nerve from the posterior cord of the brachial plexus which does Brachioradialis and ECRL
Then splits into superficial and deep branch
Superficial does ECRB
Deep does supinator and then it becomes the Posterior interosseous nerve does the rest of the extensors and pollicis muscles

Question 17

What is the cutaneous supply for the forearm

Answer 17

• Medial cutaneous nerve of the forearm on the medial side
• Lateral cutaneous nerve of the forearm (from the terminal portion of musculocutaneous nerve) for lateral side
• Posterior cutaneous nerve of forearm (from the radial nerve) for the posterior

Question 18

What gives the blood supply to the back of the forearm

Answer 18

The posterior interosseous artery (a branch of the common interosseous of the Ulnar artery). does most except distally where the anterior interosseous artery passes through a gap in the interosseous membrane to help or replace the supply.