Extensor Forearm & Dorsum of Hand

Question 1

Name the 6 superficial muscles of the extensor compartment of the forearm.

Answer 1

brachioradialis
extensor carpi radialis longus
extensor carpi radialis brevis
extensor digitorum
extensor digiti minimi
extensor carpi ulnaris

Question 2

Name the 5 deep muscles of the extensor compartment of the forearm.

Answer 2

supinator
abductor pollicis longus
extensor pollicis brevis
extensor pollicis longus
extensor indicis

Question 3

Brachioradialis
proximal attachment
distal attachment
innervation
action

Answer 3

origin: lateral supracondylar ridge of humerus
insertion: distal radius
innervation: radial nerve
action: flexes forearm at elbow joint

Question 4

Extensor carpi radialis longus
proximal attachment
distal attachment
innervation
action

Answer 4

origin: lateral supracondylar ridge of humerus
insertion: base of 2nd metacarpal
innervation: radial nerve
action: extends & abducts hand at wrist joint

Question 5

Extensor carpi radialis brevis
proximal attachment
distal attachment
innervation
action

Answer 5

origin: lateral epicondyle via common extensor tendon
insertion: base of 3rd metacarpal bone
innervation: deep branch of radial nerve
action: extends & abducts hand at wrist joint

Question 6

Extensor digitorum
proximal attachment
distal attachment
innervation
action

Answer 6

origin: lateral epicondyle via common extensor tendon
insertion: extensor expansions of all fingers
innervation: posterior interosseous nerve (continuation of radial nerve after it exits the supinator muscle)
action: extends the MP and IP joints of all fingers

Question 7

Extensor digiti minimi
proximal attachment
distal attachment
innervation
action

Answer 7

origin: lateral epicondyle via common extensor tendon
insertion: extensor expansion of little finger
innervation: posterior interosseous nerve
action: extends little finger at MP and IP joints

Question 8

Extensor carpi ulnaris
proximal attachment
distal attachment
innervation
action

Answer 8

origin: lateral epicondyle via common tender tendon and posterior ulna
insertion: base of 5th metacarpal
innervation: posterior interosseous nerve
action: extends & adducts hand at wrist joint

Question 9

Supinator
proximal attachment
distal attachment
innervation
action

Answer 9

origin: lateral epicondyle of humerus, radial collateral ligament, radial annular ligament, supinator fossa and crest of ulna
insertion: proximal radius
innervation: deep branch of radial nerve
action: supinates the forearm

Question 10

Abductor pollicis longus
proximal attachment
distal attachment
innervation
action

Answer 10

origin: posterior radius, ulna and interosseous membrane
insertion: base of 1st metacarpal
innervation: posterior interosseous nerve
action: abducts thumb, contributes to extension

Question 11

Extensor pollicis brevis
proximal attachment
distal attachment
innervation
action

Answer 11

origin: posterior radius and interosseous membrane
insertion: base of proximal phalanx of thumb
innervation: posterior interosseous nerve
action: extends the proximal phalanx of thumb

Question 12

Extensor pollicis longus
proximal attachment
distal attachment
innervation
action

Answer 12

origin: posterior ulna and interosseous membrane
insertion: base of distal phalanx of thumb
innervation: posterior interosseous nerve
action: extends distal phalanx of thumb

Question 13

Extensor indicis
proximal attachment
distal attachment
innervation
action

Answer 13

origin: posterior ulna and interosseous membrane
insertion: extensor expansion of 2nd digit
innervation: posterior interosseous nerve
action: extends all the joints of the 2nd digit

Question 14

What is the extensor retinaculum?

Answer 14

It is a fibrous band that is aligned with the palmar carpal ligament of the flexor surface. This band holds in check the long extensor tendons of the wrist.

Question 15

What is the anatomical snuffbox?
What are the boundaries of the anatomical snuffbox?
What structures traverse it?

Answer 15

The anatomical snuffbox is a hollow region on the radial side of the wrist that is evident with the thumb abducted and extended.
Its boundaries are:
tendon of extensor pollicis longus
tendons of extensor pollicis brevis & abductor pollicis longus
The radial artery traverses the floor of the snuffbox.

Question 16

Describe the extensor expansions and name the tendons that attach to them.

Answer 16

The long extensor tendons of the fingers blend with triangular fibrous sheets known as the extensor expansions. The extensor expansions overlie the MP joints (the thumb has no extensor expansion). Fibers of the extensor expansion split into one central band and two lateral bands. The central band inserts into the middle phalange and the lateral bands insert into the distal phalange of each finger. Tendons of all interossei and lumbrical muscles as well as the long extensor tendons to the fingers join the extensor expansions.

Question 17

Posterior interosseous artery

What does it branch off of?

Answer 17

arises from the common interosseous artery, which arises from the ulnar artery

Question 18

Anterior interosseous artery

What does it branch off of?

Answer 18

arises from the common interosseous artery, which arises from the ulnar artery

Question 19

Dorsal carpal arterial arch
What arteries contribute to this arch?
What do its branches supply?

Answer 19

Branches from the anterior and posterior interosseous, radial, and ulnar arteries contribute to the arch.
The arch forms three dorsal metacarpal arteries that divide into dorsal digital arteries to the 2nd, 3rd, 4th, and 5th digits

Question 20

Name the “outcropping muscles” of the extensor forearm

Answer 20

1. Abductor pollicis longus
2. Extensor pollicis brevis
3. Extensor pollicis longus

Question 21

Name the motor nerves of the extensor forearm and what they innervate

Answer 21

The radial nerve innervates brachioradialis and extensor carpi radialis longus.
The deep radial nerve supplies extensor carpi radialis brevis and supinator.
When the deep radial nerve emerges from supinator it is renamed to posterior interosseous nerve and innervates the remaining extensor forearm muscles:
extensor digitorum
extensor digiti minimi
extensor carpi ulnaris
abductor pollicis longus
extensor pollicis brevis
extensor pollicis longus
extensor indicis

Question 22

Describe the cutaneous innervation of the extensor forearm.

Answer 22

1. medial cutaneous nerve (medial cord of brachial plexus) -> medial extensor forearm
2. lateral cutaneous nerve (musculocutaneous nerve branch) -> lateral extensor forearm
3. posterior cutaneous nerve (radial nerve branch) -> posterior extensor forearm

Question 23

Describe the cutaneous innervation of the dorsum of the hand.

Answer 23

ulnar nerve: pinky, half of ring finger, and associated dorsum of hand

radial nerve: index, middle, half of ring finger (except tips of fingers), and associated dorsum of hand

median nerve: tips of index, middle, half of ring finger

Question 24

How do dermatomes relate to cutaneous innervation?

Answer 24

Dermatome maps do not coincide with cutaneous innervation maps.

The dermatome is a bilateral slice of skin supplied by fibers from one pair of spinal nerves that are usually distributed by several cutaneous nerves.

Injury to spinal nerves, their roots or rami presents as loss of sensation to dermatomal slices of skin. Injury to cutaneous nerves presents as sensation loss to patches of skin.