Session 8: Anatomy of the Anterior Forearm

Question 1

How to remember the muscles of the anterior compartment of the forearm.

Answer 1

4 - 1 = 3
Superficial (4): (lateral to medial)
Pronator teres
Flexor carpi radialis
Palmaris longus
Flexor carpi ulnaris

Intermediate (1):
Flexor digitorum superficialis

Deep (3):
Flexor digitorum profundus
Flexor pollicis longus
Pronator quadratus

Question 2

How to remember the location of the superficial muscles of the forearm.

Answer 2

Position thumb on medial epicondyle and spread fingers into forearm to resemble the four superficial flexors:
Pass/Fail/Pass/Fail

Question 3

Origin of the superficial muscles of the anterior forearm.

Any exceptions?

Answer 3

They all come from a common tendon which arises from the medial epicondyle of the humerus and is known as the common flexor origin.

Flexor carpi ulnaris has two heads and one of the heads (ulnar head) originates from the medial margin of the olecranon of the ulna.

Pronator teres has two heads and one of the heads (ulnar head) originates from the coronoid process.

Question 4

Innervation of the superficial muscles of the anterior forearm.
(Any exceptions?)

Answer 4

All innervated by the medial nerve (C6-T1) except for flexor carpi ulnaris which is innervated by the ulnar nerve (C8-T1).

Question 5

Insertion and action of: Flexor carpi ulnaris.

What passes through the two heads of the flexor carpi ulnaris?

Answer 5

Inserts onto the pisiform bone and hook of the hamate and the base of the fifth metacarpal bone.

Flexes and adducts the wrist.

The ulnar nerve passes between the two heads of FCU to enter the anterior compartment of the forearm.

Question 6

Insertion and action of: Palmaris longus

Answer 6

Inserts onto the flexor retinaculum of the wrist and the palmar aponeurosis.

Weak flexor of the wrist (can therefore be used for tendon grafting in reconstructive surgery without producing weakness).

Question 7

How do you know if you have palmaris longus?

Answer 7

Flex wrist and oppose thumb and little finger (bring together)
Palmaris longus tendon should protrude.

Question 8

Insertion and action of: Flexor carpi radialis

Answer 8

Inserts onto the base of the second and third metacarpals.

Flexes and abducts the wrist (in contrast to flexor carpi ulnaris which adducts)

Question 9

Insertion and action of: Pronator teres

What passes through the heads of the pronator teres?

Answer 9

Muscle passes laterally to insert onto the mid-shaft of the radius.

Pronates the forearm.

Median nerve passes between the two heads of pronator teres to exit the cubital fossa.

Question 10

Location, origination, insertion, innervation and action of flexor digitorum superficialis.
What passes between the heads of the FDS?

Answer 10

Location: Intermediate between deep and anterior compartments.

Two sites of origin:
Humeroulnar head = Common flexor origin of the medial epicondyle of humerus, the ulnar collateral ligament and the coronoid process of the ulna
Radial head = Proximal half of the anterior surface of the radius.

Insertion: Splits into four tendons at the wrist and travels through the carpal tunnel to insert onto the base of the MIDDLE phalanges of the four fingers.

Innervation: Median nerve (C6-T1)

Actions: Flexes the metacarpophalangealjoints and proximal interphalangeal joints of the four fingers. Also assists flexion of the wrist.

Ulnar artery and median nerve pass between the heads to travel deep to its muscle belly.

Question 11

Deep muscles of the anterior forearm:

Answer 11

Flexor digitorum profundus
Flexor pollicis longus
Pronator quadratus

Question 12

Location, origination, insertion, innervation and action of flexor digitorum profundus.

Answer 12

Originates from proximal two thirds of the shaft of the ulna and the associated interosseous membrane.

At the wrist it splits into four tendons that pass through the carpal tunnel.

Inserts onto the base of the DISTAL phalanges of the four fingers.

Actions: Only muscle that can flex the distal interphalangeal joints of the fingers. Also flexes the metacarpophalangeal joints and assists flexion of the wrist.

Innervation: Ulnar (medial) half of FDP which flexes little and ring fingers is innervated by the ulnar nerve.
Radial (lateral) half of FDP which flexes the middle and index fingers is innervated by the anterior interosseous branch of the median nerve.

Question 13

Location, origination, insertion, innervation and action of flexor pollicis longus.

Answer 13

Found on the radial side of FDP.

Originates from the middle of the anterior surface of the radial shaft and the adjacent interosseous membrane.

Inserts onto the base of the distal phalanx and the thumb.

Flexes the interphalangeal joint and metacarpophalangeal joint of the thumb.

Innervated by the anterior interosseous branch of the median nerve.

Question 14

Location, origination, insertion, innervation and action of pronator quadratus.

Answer 14

Rectangular shaped muscle which is found deep to the tendons of the FDP and FPL.

Originates from the anterior surface of the distal ulna.

Inserts onto the anterior surface of the distal radius.

Pronates the forearm at the radioulnar joints.

Innervated by the anterior interosseous branch of the median nerve.

Question 15

Muscles of the posterior compartment of the forearm. (Relevant to this session)

Answer 15

Brachioradialis
Supinator
Anconeus

Question 16

Location, origination, insertion, innervation and action of brachioradialis.

Answer 16

Originates from the proximal aspect of the lateral supracondylar ridge of the humerus.

Inserts onto the distal end of the radius proximal to the radial styloid process.

Most effective at flexing the elbow when the forearm is mid-prone. In the supinated position brachioradialis only assist flexion.

Innervated by the radial nerve(C5-T1)

Question 17

Location, origination, insertion, innervation and action of supinator.
What passes through the heads of the supinator?

Answer 17

Two origins.
Humeral head = common extensor origin on the lateral epicondyle of humerus.
Ulnar head = supinator crest on the radial border of the proximal shaft of the ulna

Wrap around the radial border of the radius

Insert together onto the proximal radial surface of the radius.

Supinates the forearm (when there is no resistance)

Innervated by the deep branch of the radial nerve.

Deep branch of radial nerve exits the cubital fossa by passing between the heads of supinator to enter the posterior compartment of the forearm.

Question 18

Location, origination, insertion, innervation and action of Anconeus.

Answer 18

Originates from the common extensor origin on the lateral epicondyle of the humerus.

Inserts onto the radial side of the olecranon and the posterior surface of the proximal ulna.

Very weak extensor of the elbow. Stabilises the elbow joint as well. During pronation ancones abducts the ulna and prevents the joint capsule from impingement within the olecranon fossa.

Innervated by the radial nerve.

Question 19

Motor function of the median nerve.

Answer 19

Innervates the flexor and pronator muscles in the anterior compartment except for flexor carpi ulnaris. Also innervated flexor digitorum superficialis and it’s anterior interosseous branch innervates the deep muscles as well (radial half of the flexor digitorum profundus)
Also supplies innervation to the thenar muscles and lateral two lumbricals in the hand.

Question 20

Sensory functions of the median nerve.

Answer 20

Small and confined to the hand.
Palmar cutaneous branch in the forearm which innervates the radial aspect of the palm and digital cutaneous branches which innervate the radial three and a half fingers (this includes the thumb) on the palmar surface of the hand. Also innervates the dorsum of the radial three and a half fingers at the distal phalanges (finger tips).

Question 21

Anatomical course of the median nerve.

Answer 21

Descends the arm from the medial and lateral cords of the brachial plexus in the axilla.
It is initially situated lateral to the brachial artery but as it goes halfway down the arm the nerve crosses over the brachial artery and becomes situated medially to the brachial artery.

Enters the anterior compartment of the forearm via the cubital fossa.

In forearm the median nerve exits the cubital fossa by travelling between the two heads of pronator teres and deep to the tendinous arch of the flexor digitorum superficialis muscle.

Passes distally between the flexor digitorum superficialis muscle and the flexor digitorum profundus muscle.

Question 22

What branches does the median give off in the forearm?

Answer 22

Anterior interosseous nerve

The median nerve also gives off the palmar cutaneous branch to innervate the skin of the lateral palm, this passes superficial to the carpal tunnel and that means it is not involved in carpal tunnel syndrome.

Question 23

After giving off the branches of the forearm, what does it give off?

Answer 23

Median nerve then enters the hand via the carpal tunnel and terminates into two branches:

Recurrent branch which innervates most of thenar muscles with exception of adductor pollicis and deep head of abductor pollicis brevis supplied by the ulnar nerve.

Palmar digital branch which innervates the palmar surface and finger tips of the radial three and a half digits.
Also innervates the lateral two lumbrical muscles which flex the metacarpophalangeal joints and extend the interphalangeal joints of the index and middle fingers.

Question 24

Motor function of the ulnar nerve.

Answer 24

Innervates the intrinsic muscles of the hand apart from the thenar muscles and lateral two lumbricals.
Also innervates two muscles in the forearm which are flexor carpi ulnaris and flexor digitorum profundus (ulnar side).

Question 25

Sensory functions of the ulnar nerve.

Answer 25

Innervates the palmar and dorsal surfaces of the ulnar one and a half fingers and the ulnar aspect of the palm and dorsum of the hand.

Question 26

Describe the anatomical course of the ulnar nerve.

Answer 26

From brachial plexus in the axilla.
Descends the medial aspect of the arm. At elbow it passes posterior to the medial epicondyle of the humerus in the cubital tunnel and gives rise to an articular branch that supplies the elbow joint.

To enter the forearm it passes between the two heads of the flexor carpi ulnaris and travels deep to FCU.

At the wrist the ulnar nerve travels superficial to the flexor retinaculum and medial to the ulnar artery. Enter the hand via the ulnar canal also called Guyon’s canal.

Terminates in the hand by giving off superficial and deep branches.

Question 27

What branches does the ulnar nerve give off in the forearm?

Answer 27

Muscular branch which innervates flexor carpi ulnaris and the ulnar half of flexor digitorum profundus.

Palmar cutaneous branch - innervates the ulnar third of the palm

Dorsal cutaneous branch - innervates the dorsal surface of the ulnar one and a half fingers and the associated dorsal area of the hand.

Question 28

Intrinsic hand muscles innervated by the deep branch of the ulnar nerve.

Answer 28

Hypothenar muscles
Ulnar two lumbricals
Adductor pollicis
Palmar and dorsal interossei of the hand
Palmaris brevis
Deep head of flexor pollicis brevis

Question 29

How can you test for ulnar nerve palsy?

Answer 29

This is specifically paralysis of the adductor pollicis.
It’s called Froment’s sign and the patient is asked to grasp a piece of paper between thumb and index finger as paper is pulled away.
If there is no palsy they should be able to hold the paper with no difficulty.

A positive test is if the patient is unable to adduct the thumb. Instead they flex the thumb at the interphalangeal joint to try to maintain a hold on the paper.

Question 30

Motor functions of the musculocutaneous nerve.

Answer 30

Innervates the anterior compartment of the arm:

Coracobrachialis, biceps brachii and brachialis.

Question 31

Sensory functions of the musculocutaneous nerve.

Answer 31

Changes its name to lateral cutaneous nerve of the forearm and innervates the lateral aspect of the forearm.

Question 32

Anatomical course of the musculocutaneous nerve.

Answer 32

Leaves axilla and pierces the coracobrachialis muscle near its point of insertion on the humerus. Gives off a branch to coracobrachialis.

Then passes down the flexor compartment of the arm superficial to brachialis but deep to biceps brachii. Innervates both these muscles and gives articular branches to the elbow.

Then pierces the deep fascia lateral to biceps brachii to emerge lateral to the biceps tendon and brachioradialis.

Continous into the forearm as the lateral cutaneous nerve of the forearm to provide sensory innervation to the lateral aspect of the forearm.

Question 33

Why are injuries to the musculocutaneous nerve uncommon? Mechanism of injury

Answer 33

Well protected in axilla.

Stabbing or anterior dislocation of the shoulder.

Question 34

Sensory and motor function loss of damage to the musculocutaneous nerve.

Answer 34

Coracobrachialis, biceps brachii and brachialis paralysed. Flexion at shoulder and elbow weakened. Supination weakened.

Loss of sensation over the radial side of the forearm.

Question 35

Why is motor function only weakened?

Answer 35

Because pectorals major and brachioradialis can still flex shoulder and elbow flexion respectively.
Supination is only weakened due to supinator.

Question 36

Which nerve does the medial cutaneous nerve of the arm arise from?
Distribution.

Answer 36

The medial cord of the brachial plexus and contains T1 fibres.
Distributed to the skin of the distal medial arm as far as the elbow. Communicates with the intercostobrachial nerve (T2) so there is some overlapping between T1 and T2.

Question 37

Which nerve does the medial cutaneous nerve of the forearm arise from?
Distribution.

Answer 37

Medial cord of the brachial plexus (C8-T1)

Supplies skin on the distal anterior surface of the arm and ulnar side of the forearm as far as the wrist.

Question 38

What does the radial nerve innervate?

Answer 38

Posterior compartment of the arm and forearm.

Passes through the cubital fossa.

Question 39

Arteries of the forearm.

Answer 39

Radial and ulnar arteries. They both anastomose in the hand by forming two arches: the superficial palmar arch and the deep palmar arch.

Question 40

Anatomical course of the radial artery and supply.

Answer 40

Bifurcation of the brachial artery within the cubital fossa. Supplies the posterolateral aspect of the forearm. Contributes to anastomotic networks surrounding the elbow joint and carpal bones.

Question 41

Anatomical course of the ulnar artery and supply.

Answer 41

Bifurcation of the brachial artery within the cubital fossa.
Supplies the anteromedial aspect of the forearm. Contributes to an anastomotic network surrounding the elbow joint and also gives rise to the anterior and posterior interosseous arteries which supply the deeper structures in the forearm.

Question 42

Where can the brachial pulse be palpated?

Answer 42

In the cubital fossa immediately medial to the tendon of the biceps brachii. Also where you put stethoscope to hear korotkoff sounds when measuring blood pressure.

Question 43

Where can the radial pulse be palpated?

Answer 43

At the wrist immediately radial to the prominent tendon of the flexor carpi radialis muscle.

Question 44

Where can the ulnar pulse be palpated?

Answer 44

Wrist, immediately radial to the tendon of flexor carpi ulnaris and proximal to the pisiform bone.

Question 45

Superficial veins are considered to form part of the roof of the cubital fossa. Which?

Answer 45

Basilic vein (Medial)
Cephalic vein (lateral)
Median cubital vein (connection between basilic and cephalic)

Question 46

The anatomy of the superficial venous system can vary a lot but there are two common variants. Which?

Answer 46

Basilic vein and cephalic vein with a median cubital vein connecting the two.

Basilic vein and cephalic vein with branches (median basilic vein and median cephalic vein) anastomosing into a median vein of forearm.

Question 47

What are the venae comitantes (deep venous system) in the upper limb called?

Answer 47

The deep veins share the same name of the artery they accompany.

Question 48

Where can you find the brachial veins?

Answer 48

Either side of the brachial artery.

Question 49

Where can you find the radial and ulnar veins?

Answer 49

Close to the radial and ulnar arteries respectively.

Question 50

What is the cubital fossa?

Answer 50

A depression, anterior to the elbow joint of a triangular shape.

Question 51

Borders of the cubital fossa.

Answer 51

Lateral border = medial border of brachioradialis
Medial border = lateral border of pronator teres
Superior border = hypothetical line between the epicondyles
Floor = proximally by brachialis and distally by supinator
Roof = skin, fascia, bicipital aponeurosis and superficial veins like the median cubital vein. Also medial cuteness nerve of forearm and the lateral cutaneous nerve of the forearm.

Question 52

Contents of the cubital fossa (lateral to medial)

Answer 52

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Radial nerve
Biceps tendon
Brachial artery
Median nerve