Part 8: Posterior Compartment of the Forearm

Question 1

Brachioradialis origin, insertion, action and innervation

Answer 1

O: Upper 2/3 lat supracondylar ridge humerus
I: Base styloid process radius
A: Flexes elbow, weak pronation (to neutral)
N: Radial (5,6)

Question 2

Extensor Carpi Radialis Longus origin, insertion, action and innervation

Answer 2

O: Lower 2/3 lat supracondylar ridge humerus
I: Posterior base 2nd MC
A: Extends and abducts wrist
N: Posterior interosseous n (branch of radial - C6,7)

Question 3

Extensor Carpi Radialis Brevis origin, insertion, action and innervation

Answer 3

O: CEO
I: Posterior base 2nd MC
A: Extends and abducts wrist joint
N: Posterior interosseous n (branch of radial - C6,7)

Question 4

Describe the common extensor origin

What arises from it?

Answer 4

smooth area in front of lateral epicondyle

ECRB, ED, EDM, ECU

Question 5

Extensor digitorum origin, insertion, action and innervation

Answer 5

O: CEO
I: Extensor expansion of all 4 fingers
A: Extends fingers
N: PIN (branch of radial - C7,8)

Question 6

Extensor digiti minimi origin, insertion, action and innervation

Answer 6

O: CEO
I: Extensor expansion of little finger (usually 2 tendons)
A: Extends little finger
N: PIN (branch of radial - C7,8)

Question 7

Extensor carpi ulnaris origin, insertion, action and innervation

Answer 7

O: CEO and aponeurotic sheath ulna
I: Base 5th MC via groove ulnar styloid
A: Extends and Adducts at wrist
N: PIN (C6,7)

Question 8

Aconeus origin, insertion, action and innervation

Answer 8

O: Lower lat epicondyle
I: Lateral side olecranon
A: Weak elbow extensor
N: Radial n (C7,8)

Question 9

Supinator origin, insertion, action and innervation

Answer 9

O: Deep part - supinator crest and fossa of ulna
Superficial part - lat epicondyle and lat lig of elbow
I: Neck and shaft of radius
A: Supination (only acts alone in extended elbow)
N: PIN (C5,6) - passes between the two parts

Question 10

Abductor Pollicis Longus origin, insertion, action and innervation

Answer 10

O: Upper post ulnar and radius and IOM
I: Base 1MC and trapezium
A: Abducts thumb
N: PIN (C7,8)

Question 11

Extensor pollicis brevis origin, insertion, action and innervation

Answer 11

O: Lower 1/3 post radius and IOM
I: Base proximal phalanx
A: Extends MPCJ of thumb
N: PIN (C7,8)

Question 12

Extensor pollicis longus origin, insertion, action and innervation

Answer 12

O: Middle 1/3 posterior ulnar and IOM
I: Base distal phalanx
A: Extends IPJ and MCPJ of thumb
N: PIN (C7,8)

Question 13

Extensor Indicis origin, insertion, action and innervation

Answer 13

O: Lower post shaft of ulna and IOM
I: Extensor expansion of index finger
A: Extension of PIPJ and DIPJ of index finger
N: PIN (C7,8)

Question 14

Describe the borders of the anatomical snuffbox

and bony floor

Answer 14

Ulnar side - EPL
Radial side - EPB and APL
Proximally radial styloid then scaphoid, trapezium and then base MC of thumb distally

Question 15

Important structures in the anatomical snuffbox

Answer 15

radial artery

cephalic vein begins in snuffbox

Question 16

Path of posterior interosseous nerve

Answer 16

Branch of radial at elbow, passes between deep and superficial supinator, appears in extensor compartment and goes over APL to IOM. Supplies muscles from CEO and deep muscles

Question 17

Describe the extensor retinaculum

Answer 17

Ribbon band lies obliquely across distal extensor surface of wrist. Proximally attached near styloid process and distally to pisiform and triquetreum. Not attached to ulnar.
Extensor tunnel divided into 6 compartments.