GA7: Posterior Forearm & Hand

Question 1

No fibrous digital sheaths, osseofibrous tunnels, or synovial tendon sheaths are on the ________ of the digits.

Answer 1

dorsum

Question 2

What is the extension retinaculum?

Answer 2

Thickening of the investing deep fascia of the forearm to hold extension tendons in place across the back of the wrist. Beneath it are six separate osseofibrous tunnels and synovial tendon sheaths.

Question 3

What is abduction of the hand also called?

Answer 3

Radial deviation

Question 4

What is adduction of the hand also called?

Answer 4

Ulnar deviation

Question 5

What are the other names for the posterior muscle group of the forearm?

Answer 5

Dorsal, radiodorsal, extension, or extension/supinator muscle group of the forearm

Question 6

What nerve innervates the posterior muscle group of the forearm?

Answer 6

The radial nerve

Question 7

What muscles are included in the superficial layer of the posterior muscle group of the forearm?

Answer 7

Lateral to medial: Brachioradialis, extension carpi radialis longus, extension carpi radialis brevis, extension digitorum, extensor digit Minami (quinti), extension carpi ulnaris, and anconeus

Question 8

Brachioradialis: Origin, Insertion, Action

Answer 8

Origin: Lateral supracondylar ridge of humerus
Insertion: Distal end of the radius near the styloid process
Action: Flexes the elbow

Question 9

Extensor carpi radialis longus: Origin, Insertion, Action

Answer 9

Origin: Lateral supracondylar ridge (distally)
Insertion: Base of second metacarpal
Action: Extends and abducts the wrist

Question 10

Extensor carpi radialis brevis: Origin, Insertion, Action

Answer 10

Origin: Lateral epicondyle of the humerus (common extension origin)
Insertion: Base of the third metacarpal
Action: Extends the wrist, weakly abducts the wrist

Question 11

Extensor digitorum: Origin, Insertion, Action

Answer 11

Origin: Lateral epicondyle
Insertion: Tendons go to digits II, III, IV and often V. Each tendon becomes flat and after weakly inserting on the base of the proximal phalanx, splits into a central band and two side bands.
Action: Extends the MP joint, extends the proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints

Question 12

Where does the central band of the extensor digitorum insert?

Answer 12

The base of the middle phalanx

Question 13

Where do the side-bands of the extensor digitorum insert?

Answer 13

The base of the distal phalanx

Question 14

What is the extensor tendon assembly?

Answer 14

1. Tendons of interosseus and lumbrical muscles unite with central band and side-bands.
2. Over proximal phalanx and metavarpophalangeal (MP) joint an aponeurotic sheet (extension expansion or hood) unites all of these tendons. Deep layer of extension expansion (sagittal band) passes on each side of MP joint and attaches to palmar side of its capsule. Sagittal bands hold extensor digitorum (ED) tendon in place, preventing “bowstringing” during full extension (hyper-extension) of MP joint. Sometimes sagittal band is called the hood or sling and the triangular superficial part of expansion is called the extension expansion or wing.

Question 15

What is another word for the sagittal band?

Answer 15

The hood/sling

Question 16

What is another word for the triangular superficial part of expansion?

Answer 16

The Extension expansion or wing

Question 17

Extension digit Minami (quinti): Origin, Insertion, Action

Answer 17

Origin: Lateral epicondyle
Insertion: Joins ED tendon of little finger
Action: Same actions as ED but only for digit V - extends the MP joint

Question 18

Extension Carpi Ulnaris: Origin, Insertion, Action

Answer 18

Origin: Lateral epicondyle and posterior border of the Ulnar
Insertion: Base of fifth metacarpal
Action: Extends and adducts wrist, assists in extending the elbow

Question 19

Anconeus: Origin, Insertion, Action

Answer 19

Origin: Posterior side of the lateral epicondyle
Insertion: Lateral side of the proximal part of the ulna, including the olecranon
Actions: assets triceps in extending the forearm, stabilizes the elbow joint.

Question 20

What are the muscles in the deep layer of the forearm?

Answer 20

Supinator, Abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, extensor indicis, anatomical snuffbox

Question 21

Supinator: Origin, Insertion, Action

Answer 21

Origin: Lateral epicondyle, radial collateral ligament of the elbow, and lateral side of the proximal part of the ulna
Insertion: Spirals around the proximal part of the radius to insert on its posterior, lateral, and anterior sides
Actions: Supinates forearm by swiveling radius, less powerfully than biceps unless elbow is extended.

Question 22

What are the outcropping muscles?

Answer 22

They all originate from interosseous membrane and adjacent parts of the radius and/or ulna. Their tendons emerge (outcrop) between tendons of superficial muscles

Question 23

Abductor pollicis longus: Insertion, Action

Answer 23

Insertion: Base of the first metacarpal, laterally
Actions: Abducts and extends the first carpometacarpal (CM) joint and abducts the wrist

Question 24

Extensor pollicis Bevis: Insertion, Action

Answer 24

Insertion: Base of the proximal phalanx of the thumb
Action: extends CM and MP joints of thumb and abducts the wrists

Question 25

Extensor pollicis longus: Insertion, Action

Answer 25

Insertion: Base of the distal phalanx of the thumb
Action: Extends all joints of the thumb (CM, MP, and IP). It also extends the wrist.
**Tendon bends around the dorsal tubercle of the radius

Question 26

Extensor indicis: Insertion, Action

Answer 26

Insertion: Joins ED tendon to index finger
Action: Same actions as ED but only on digit II

Question 27

Describe the Anatomical Snuffbox

Answer 27

Depression between tendons of extension pollicis brevis and longus. A fractured scaphoid is tender here. The radial artery passes through the snuffbox but its pulse is hard to detect because of tough overlying fascia.

Question 28

If other MP joints are kept from extending, you can easily extend the MP joint of the index finger and the little finger, but not that of digits III of IV. What factors are involved in this restraint?

Answer 28

1. Index and little fingers have their own private extensor muscles (EI and EDM).
2. Intertendinous connections between ED tendons on the back of the hand restrain adjacent tendons - usually exist on both sides of digits III and IV, but only on one side of digits II and V.
3. Intertendinous connections between tendons of flexor digitorum profundus to digits III, IV and V (these connections are proximal to wrist)
4. Deep transverse metacarpal ligaments restrain adjacent digits. Present on both sides of digits III and IV but only on one side of digits II and V.

Question 29

Where does the radial nerve arise?

Answer 29

The posterior cord of the brachial plexus

Question 30

Where does the radial nerve course?

Answer 30

It courses inferiorly and laterally along the posterior aspect of the humerus in the spiral course (along the spiral groove)

Question 31

What holds the radial nerve against the humerus?

Answer 31

The long and lateral heads of the triceps brachii; it is susceptible to injury if the humerus is fractured

Question 32

The radial nerve gives off the ______________ of the forearm then passes anterior to the ____________________, hidden by brachioradialis muscle

Answer 32

posterior cutaneous nerve, lateral epicondyle of humerus

Question 33

Deep to the brachioradialis muscle, the radial nerve innervates what?

Answer 33

The anconeus, brachioradialis, and extensor carpi radialis longus, and then splits into two terminal branches

Question 34

What are the two terminal branches of the radial nerve?

Answer 34

1. Superficial radial nerve supplies skin on the posterior side of the forearm and head
2. Deep radial nerve penetrates Supinator and supplies all other muscles of the posterior forearm. On emerging from Supinator it is called posterior interosseous nerve (sometimes used synonymously for entire deep radial nerve)

Question 35

Give three examples if muscles were denervated:

Answer 35

1. There will be reduced strength for any movements they take part in, and they will gradually atrophy
2. If other muscles can perform these actions, they will hypertrophy in an attempt to compensate
3. There may be eventual contracture deformity resulting from shortening of unopposed antagonists

Question 36

What will happen if cutaneous supply is affected?

Answer 36

There will be reduced skin sensation in the territory supplied, but because of overlapping distributions there may be no area of total anesthesia. If a major nerve is cut there is often total anesthesia in parts of its cutaneous territory

Question 37

What would happen if the radial nerve was severed high in brachium?

Answer 37

A. Inability to extend elbow (if injury is high enough to completely denervate triceps), wrist, and MP joints. IP joints can still be extended by interossei and lumbricals. Weakened supination and abduction and addiction of wrist. Eventual flexion deformity of these joints (elbow, wrist, MP) and addiction deformity of wrist, if not prevented by physiotherapy. Atrophy of triceps and posterior forearm muscles.
B. Reduced skin sensation down posterior side of arm, forearm, and lateral part of hand. Some total anesthesia.

Question 38

What does the Ulnar artery give off?

Answer 38

The common interosseous artery, which splits into the anterior and posterior interosseous arteries

Question 39

Where does the posterior interosseous artery supply blood?

Answer 39

The posterior interosseous artery is a major source of blood to dorsal forearm muscles and runs with posterior interosseous nerve distal to Supinator muscle

Question 40

Describe the dorsal carpal arterial rate (plexus).

Answer 40

1. Formed by branches of radial and Ulnar arteries

2. Gives off branches to dorsum of hand and digits

Question 41

Describe the radial artery.

Answer 41

The radial artery passes through anatomical snuffbox and ends as deep palmar branch (to deep palmar arterial arch) and a branch to dorsal side of index finger.

Question 42

What happens during the 4th week of embryonic development?

Answer 42

The limb buds become visible as small elevations from the ventrolateral body wall.

Question 43

What happens at 6 weeks of embryonic development?

Answer 43

The limb buds flatten to form the hand and foot plates. Mesenchymal tissue has condensed to form digital rays; notches between the digital rays form by the break down of loose mesenchyme in the intervals between the digital rays. The headline cartilage model is formed by the 6th week.

Question 44

What is apoptosis?

Answer 44

Programmed cell death that is responsible for the separation of the palate into individual fingers and toes.

Question 45

When does ossification begin in embryonic development?

Answer 45

Ossification begins by the end of the 8th week.

Question 46

Describe the diaphysis and epiphyses at birth.

Answer 46

At birth, the diaphysis (shaft) of the bone is usually completely ossified, but the epiphyses (two ends) are still cartilaginous.

Question 47

What are the three categories of limb abnormalities?

Answer 47

1. Reduction defects - part of the limb (Meromelia) or an entire limb (Amelia) is missing
2. Duplication defects - extra limb parts are present (polydactyly, or extra digits)
3. Dysplasia - malformation of limb parts. Syndactyly is fusion of digits.