Forearm

Question 1

(a) Name the parts/bony landmarks of the ulna.
(b) How would you side the ulna.

Answer 1

(a) trochlear notch, radial notch, olecranon process, coronoid process, ulnar tuberosity, shaft, interosseous (lateral) border of the shaft, styloid process
(b) 1. the trochlear notch, olecranon process and coronoid process are proximal, 2. the trochlear notch faces anteriorly, 3. The sharp crest-like interosseous border of the shaft is directed laterally.

[Image] [Diagram ]
Use an atlas too!

Question 2

Describe the sensory innervation of the forearm. (Hint: territory; nerve, its root values and origin)

Answer 2

1. Medial side of the forearm - medial antebrachial cutaneous nerve (C8, T1) from the medial cord of the brachial plexus (becomes cutaneous halfway down the arm along the basilic vein)
2. Lateral side of the forearm - lateral antebrachial cutaneous nerve (C5, C6) from musculocutaneous nerve (emerges at the lateral border of the biceps and divides into anterior and posterior branches)
3. Posterior side of the forearm - posterior antebrachial cutaneous nerve (C6, C7, C8) from radial nerve (It runs down the posterior aspect of forearm up to the wrist)
4. [Diagram]

Question 3

State the dermatome over:
a) lateral side of the forearm
b) medial side of the forearm

Answer 3

a) C6
b) C8

Question 4

What divides the forearm into anterior and posterior compartments.

Answer 4

deep fascia of the forearm (antebrachial fascia), together with interosseous membrane and fibrous intermuscular septa
[Diagram]

Question 5

List the superficial muscles of the front of the forearm from lateral to medial. [5 muscles]

Answer 5

1. Pronator teres
2. Flexor carpi radialis
3. Palmaris longus
4. Flexor digitorum superficialis
5. Flexor carpi ulnaris
6. [Diagram] … note that FDS muscle is deep to the other 4 superficial muscles but in terms of orientation from their common flexor origin, it is lateral to FCU.

Question 6

The superficial muscles of the forearm have a common flexor origin. Where is it?

Answer 6

Medial epicondyle of humerus
[Pronator teres, FCU and FDS have another origin besides this one because they have 2 heads of origin]

Question 7

Discuss pronator teres under the following subheadings:
a) Origin
b) Insertion
c) Nerve supply
d) Actions (2)

Answer 7

a) Origin:
Superficial (Humeral) head - medial epicondyle of the humerus (above common flexor origin)
Deep (Ulnar) head - medial margin of the coronoid process of the ulna
b) Insertion: rough impression on the middle 1/3 of the lateral surface (most convex part) of the radius
c) Nerve supply: median nerve
d) Actions:
- main pronator of the forearm
- helps in the flexion of elbow

Question 8

Median nerve does not pass between the two heads of pronator teres. TRUE or FALSE?

Answer 8

FALSE

Question 9

Ulnar artery is separated from the median nerve by the deep head of pronator teres in the region of cubital fossa. TRUE or FALSE?

Answer 9

TRUE
[Diagram]

Question 10

Discuss flexor carpi radialis under the following subheadings:
1. Insertion
2. Nerve supply
3. Actions (2)

(The origin is kinda obvious.)

Answer 10

Insertion: On to the anterior aspects of the bases of second and third metacarpals.
Nerve supply: Median nerve
Actions:
1. it flexes the wrist
2. it abducts the wrist

Question 11

The tendon of flexor carpi radialis (FCR) is a good guide to the radial artery, which lies just lateral to it at the wrist. True or False?

Answer 11

True

Question 12

Discuss palmaris longus under:
1. Insertion
2. Nerve supply
3. Actions

Note: This muscle corresponds to plantaris muscle. It is a degenerating muscle with small short belly and a long tendon. It is absent on one or both sides (usually on the left) in approximately 10% of people, but its actions are not missed. Hence, its tendon is often used by the surgeons for tendon grafting.

Answer 12

1. Insertion: distal part of flexor retinaculum and palmar aponeurosis
2. Nerve supply: median nerve
3. Actions: flexes the wrist and makes palmar aponeurosis tense

Question 13

Discuss flexor carpi ulnaris under the following subheadings:
1. Origin (Hint: 2 heads of origin)
2. Insertion: 2 insertions, but one of them is the true insertion. Which and why?
3. Nerve supply
4. Actions (2)

Answer 13

(a) Origin:
small humeral head: common flexor origin which is …
large ulnar head: medial margin of the olecranon process, an aponeurosis from the upper 2/3 of the posterior border of the ulna

(b) Insertion:
- pisiform bone
- hook of hamate and the base of fifth metacarpal bone through pisohamate ligament and pisometacarpal ligament respectively.
The insertion at the hook of hamate and the base of fifth metacarpal bone is the true insertion because a sesamoid bone, the pisiform, develops in its tendon.

(c) Nerve supply: By the ulnar nerve

(d) Actions:
1. it adducts the wrist joint
2. it flexes the wrist joint

(e) [Diagram 1] [Diagram 2]

Question 14

True or False?
The ulnar nerve enters the forearm by passing between the two heads of pronator teres, which are connected to each other by an aponeurotic arch.

Answer 14

FALSE. It enters the forearm by passing between the two heads of flexor carpi ulnaris, connected to each other by a tendinous arch. [Diagram]

Question 15

Discuss the flexor digitorum superficialis under the following subheadings:
(a) Origin (has two heads)
(b) Insertion
(c) Mode of insertion
(d) Nerve supply
(e) Actions

Answer 15

(a) Origin:
humero-ulnar head:
- medial epicondyle of humerus
- sublime tubercle on the medial margin of the coronoid process of ulna
- medial (ulnar) collateral ligament of the elbow joint

radial head:
- anterior oblique line of the radius, extending from the radial tuberosity to the insertion of pronator teres (upper half of anterior border of radius)

(b) Insertion: middle phalanges of medial four fingers

(c) Mode of insertion:
The muscls splits into two layers: superficial and deep. The superficial layer forms two tendons, which are inserted into middle phalanges of middle and ring fingers. The deep layer also forms two tendons, which are inserted into middle phalanges of index and little fingers. Before insertion each of the four tendons splits, opposite the proximal phalanx, into medial and lateral slips, which are inserted into the corresponding sides of the middle phalanx.

(d) Nerve supply: median nerve

(e) Actions:
- flexes the proximal interphalangeal joints of the medial four digits
- it also helps in flexion of the proximal phalanges and wrist joint

[Diagram] [4-minute video]

Question 16

True or False?
The median nerve and ulnar artery pass downwards deep to the fibrous arch/tendinous arch connecting the humero-ulnar and radial heads of flexor digitorum superficialis.

Answer 16

True
[Diagram 1] [Diagram 2]

Question 17

List the 3 deep muscles of the front of the forearm.

Answer 17

Flexor pollicis longus (placed laterally)
Flexor digitorum profundus (placed medially)
Pronator quadratus (placed distally)
[Diagram]

Question 18

Discuss flexor digitorum profundus under the following headings: origin, insertion, nerve supply, and actions.

Answer 18

Origin:
1. From upper three-fourths of the anterior surface of the shaft of the ulna.
2. Adjacent part of the interosseous membrane.
3. The coronoid process of the ulna.

Insertion: On to the palmar aspect of the bases of distal phalanges of medial four digits.

Nerve supply:
Medial half: ulnar nerve
Lateral half: anterior interosseous nerve, a branch of the median nerve

Actions:
~ flexes the distal interphalangeal joints of medial four digits
~ helps to flex the wrist joint

[Diagram] [Cadaveric image 1] [Cadaveric image 2]

Further notes:
Flexor digitorum profundus provides origin to the lumbrical muscles in the palm.

Question 19

Discuss flexor pollicis longus under the following subheadings:
a) Origin
b) Insertion
c) Innervation
d) Actions

Answer 19

a) Origin: upper 2/3 of the anterior surface of the radius between the radial tuberosity and the insertion of pronator quadratus, as well as the adjoining part of the interosseous membrane
b) Insertion: anterior surface of the base of distal phalanx of the thumb
c) Innervation: anterior interosseous branch of the median nerve (C7, 8).
d) Actions:
- primarily flexes the distal phalanx of the thumb
- secondarily flexes proximal phalanx and first metacarpal at the metacarpophalangeal and carpometacarpal joints respectively.

[Diagram]

Question 20

True or False?
I. The anterior interosseous nerve and vessels descend on interosseous membrane between flexor pollicis longus and flexor digitorum profundus.
II. The flexor pollicis longus is not the only muscle, which flexes the interphalangeal joints of the thumb.

Answer 20

I. true
II. false

Question 21

Discuss the pronator quadratus muscle under:
1. Origin
2. Insertion (Hint: superficial and deep fibres)
3. Nerve supply
4. Actions

Answer 21

a) Origin: oblique ridge on the lower one-fourth of the anterior surface of the shaft of ulna and medial part of this surface.

b) Insertion:
1. The superficial fibres into the distal one-fourth of the anterior border and anterior surface of the shaft of radius.
2. The deeper fibres into the triangular area above the ulnar notch of the radius.

c) Nerve supply: By anterior interosseous nerve

d) Action: Pronator quadratus is the chief pronator of the forearm and is assisted by pronator teres only in rapid and forceful pronation.

[Cadaver] [Anterior interosseous nerve lesions]

Question 22

List the structures lying in front of the conventional wrist from lateral to medial side. (7)

Answer 22

1. Radial artery
2. Tendon of flexor carpi radialis
3. Tendon of palmaris longus
4. Flexor digitorum superficialis
5. Ulnar artery
6. Ulnar nerve
7. Tendon of flexor carpi ulnaris

Median nerve lies deep to the palmaris longus tendon.

Question 23

The flexor retinaculum (transverse carpal ligament, or anterior annular ligament) is a fibrous band on the palmar side of the hand near the wrist. It arches over the carpal bones of the hands, covering them and forming the carpal tunnel. List the structures that run in the carpal tunnel from lateral to medial.

Answer 23

Flexor pollicis longus tendon
Median nerve
Flexor digitorum profundus tendons
Flexor digitorum superficialis tendons
[NB// Flexor carpi radialis tendon is not within the carpal tunnel itself]

Question 24

List the 7 superficial muscles of the posterior compartment of the arm.

Answer 24

1. Brachioradialis
2. Extensor carpi radialis longus
3. Extensor carpi radialis brevis
4. Extensor digitorum
5. Extensor digiti minimi
6. Extensor carpi ulnaris
7. Anconeus
8. [Diagram: Attachments of muscles of forearm, posterior view]

Question 25

List the 5 deep muscles of the posterior compartment of the arm.

Answer 25

1. Supinator
2. Abductor pollicis longus
3. Extensor pollicis brevis
4. Extensor pollicis longus
5. Extensor indicis
6. [Diagram: Attachments of muscles of forearm, posterior view]

Question 26

The posterior interosseous nerve innervates all the muscles of the posterior compartment of the arm except 3 muscles namely: _________________.
These three muscles are supplied by the _______ nerve.

Answer 26

1. brachioradialis
2. extensor carpi radialis longus
3. anconeus
4. These muscles are supplied by the radial nerve.

Question 27

All the superficial muscles of the posterior compartment of the arm arise from the common extensor origin except three muscles, namely: ______________. What is the common extensor origin?

Answer 27

brachioradialis, extensor carpi radialis longus, anconeus

The common extensor origin is the tip of the lateral epicondyle of the humerus.

Question 28

All the superficial muscles of the posterior compartment of the arm extend the hand except which two?

Answer 28

1. anconeus
2. brachioradialis

Question 29

What superficial muscles of the back of the forearm are in the:
a) lateral group
b) posterior group
NB: All these 7 muscles cross the elbow joint.

Answer 29

a) Lateral group:
Brachioradialis
Extensor carpi radialis longus
Extensor carpi radialis brevis

b) Posterior group:
Extensor digitorum
Extensor digiti minimi
Extensor carpi ulnaris
Anconeus

Question 30

Describe the origin, insertion, innervation and actions of brachioradialis. (Note: has 3 actions)

Answer 30

(1) Origin: upper 2/3 of the lateral supracondylar ridge of the humerus
(2) Insertion: lateral surface of the distal end of the radius just above the styloid process
(3) Innervation: radial nerve
(4) Actions: (1) flexion of the elbow joint, (2) pronates the supinated forearm to midprone position (3) supinates the pronated forearm to midprone position
[Diagram] [Cadaveric image 1] [Cadaveric image 2]

Further notes:
[2-minute video]: living anatomy of the Brachioradialis muscle

Question 31

Describe extensor carpi radialis longus (ECRL) under the following subheadings:
(1) Origin
(2) Insertion
(3) Innervation
(4) Actions (2 actions)

Answer 31

(1) Origin: Lower 1/3 of the lateral supracondylar ridge of the humerus
(2) Insertion: Lateral side of the dorsal surface of the base of second metacarpal bone
(3) Innervation: Radial nerve
(4) Actions:
(a) extends the wrist
(b) abducts the wrist

Question 32

Describe the origin, insertion, innervation and action of anconeus.

Answer 32

(1) Origin: posterior aspect of lateral epicondyle
(2) Insertion: lateral side of the olecranon process and upper 1/4 of the posterior surface of the ulna.
(3) Innervation: Nerve to anconeus, which arises from radial nerve in spiral groove and descends through medial head of the triceps brachii
(4) Action: weak extensor of elbow joint
[Diagram] [2-minute video]: Anconeus - Kenhub

Further notes:
[1-minute video]: living anatomy of the Anconeus muscle

Question 33

Describe the origin, insertion, innervation and actions of extensor carpi radialis brevis.

Answer 33

(a) Origin: common tendon from the anterior aspect of the lateral epicondyle of the humerus (common extensor origin)
(b) Insertion: lateral side of the dorsal surface of the base of the third metacarpal bone
(c) Innervation: posterior interosseous nerve before piercing the supinator
(d) Action: extends and abducts the hand at the wrist joint
(e) [Diagram: origin and insertion]

Question 34

Describe the origin, insertion, innervation and actions of extensor digitorum.

Answer 34

(a) Origin: common tendon from the anterior aspect of lateral epicondyle
(b) Insertion: gives rise to four tendons for medial four digits, inserts by the extensor expansion into the dorsum of middle and terminal phalanges
(c) Innervation: posterior interosseous nerve
(d) Actions: extends the medial four digits (extension of all joints of the medial 4 fingers), can also extend the wrist

Further notes:
The extensor expansion is a complex aponeurotic extension of the extensor tendons that form as the tendons pass over the dorsal aspect of the digits. Each extensor expansion is triangular shaped with its base wrapped around the sides of the metacarpophalangeal joint. [Diagram]

Question 35

Describe the origin, insertion, innervation and actions of extensor digiti minimi.

Answer 35

a) Origin: common tendon from the anterior aspect of the lateral epicondyle
b) Insertion: through the extensor expansion, it is inserted into the dorsum of middle and terminal phalanges of little finger
c) Innervation: posterior interosseous nerve
d) Actions: extends the little finger (extension of all joints of the little finger), helps in extension of the wrist

Question 36

Describe the origin, insertion, innervation and actions of extensor carpi ulnaris.

Answer 36

a) Origin: anterior aspect of lateral epicondyle of humerus (common extensor origin)
b) Insertion: base of fifth metacarpal bone
c) Innervation: posterior interosseous nerve
d) Actions: extends and adducts the hand at the wrist joint

Question 37

Name three main extensors of the wrist.

Answer 37

Extensor carpi radialis longs, extensor carpi radialis brevis, extensor carpi ulnaris

Question 38

Name three abductors of the wrist.

Answer 38

extensor carpi radialis longus, extensor carpi radialis brevis, flexor carpi radialis

Question 39

Name two adductors of the wrist.

Answer 39

extensor carpi ulnaris, flexor carpi ulnaris

Question 40

Describe the origin, insertion, innervation and actions of supinator.

Answer 40

a) Origin: (1) lateral epicondyle of humerus, (2) annular ligament of proximal radioulnar joint, (3) supinator crest of ulna and depression behind it
b) Insertion: upper third of anterior, posterior and lateral surfaces of radius.
c) Innervation: posterior interosseous nerve before piercing supinator
d) Actions: supination of the forearm when the elbow is extended
[Diagram]

Question 41

Describe the origin, insertion, innervation and actions of abductor pollicis longus.

Answer 41

(a) Origin: (1) lateral part of the posterior surface of the ulna below anconeus, (2) middle 1/3 of the posterior surface of the radius, (3) intervening posterior surface of the interosseous membrane
(b) Insertion: lateral side of the base of the first metacarpal
(c) Innervation: posterior interosseous nerve
(d) Action: abducts the thumb
(e) [Diagram: origin and insertion]

Question 42

Describe the origin, insertion, innervation and actions of extensor pollicis brevis.

Answer 42

a) Origin: posterior surface of shaft of radius below abductor pollicis longus and adjoining surface of the interosseous membrane
b) Insertion: dorsal surface of the base of the proximal phalanx of the thumb
c) Innervation: posterior interosseous nerve
d) Actions: extends the thumb at metacarpophalangeal joint and extends the carpometacarpal joint

Question 43

Describe the origin, insertion, innervation and actions of extensor pollicis longus.

Answer 43

a) Origin: lateral part of middle 1/3 of posterior surface of ulna and adjoining interosseous membrane
b) Insertion: dorsal surface of the base of the distal phalanx of thumb
c) Innervation: posterior interosseous nerve
d) Actions: 1. extends joints of the thumb, 2. helps in extension of the wrist

Question 44

Describe the origin, insertion, innervation and actions of extensor indicis.

Answer 44

1. Origin: from the posterior surface of ulna below the origin of extensor pollicis longus and also from the adjoining interosseous membrane
2. Insertion: The tendon lies medial to the extensor digitorum tendon for the index finger. Through the extensor expansion, it is inserted into the dorsum of middle and distal phalanges of the index finger.
3. Innervation: posterior interosseous nerve
4. Actions: extends the index finger, helps in extension of the wrist

Question 45

Muscles of the anterior compartment of the arm are supplied by the ___(a)___ nerve except ____(b)____ and ____(c)____, which are supplied by the ___(d)___ nerve.

Answer 45

a) median nerve
b) flexor carpi ulnaris
c) medial 1/2 of flexor digitorum profundus
d) ulnar nerve

Question 46

Here are some MRI images of the forearm. Click on Answer to view them.

Answer 46

[Image 1] [Image 2] [Image 3] [Image 4] [Image 5: Transverse section of elbow joint]