30. Anatomy of the anterior forearm

Question 1

What are the superficial muscles of the anterior forearm and where do they originate from?

Answer 1

• pronator teres
• flexor carpi radialis
• palmaris longus
• Flexor carpi ulnaris
• originate from the medial epicondyle of the humerus. This is known as the common flexor origin

Question 2

Where are the superficial muscles relative to each other?

Answer 2

From medial to lateral: Flexor carpi ulnaris, palmaris longus, flexor carpi radialis and pronator teres

Question 3

Describe the Flexor Carpi Ulnaris:
• Where does it originate
• Where does it insert
• What is its action
• What is it innervated by

Answer 3

• Flexor carpi ulnaris (FCU) has two heads:
- The humeral head originates from the common flexor origin on the medial epicondyle of the humerus, together with the other superficial flexors.
- The ulnar head originates on the medial margin of the olecranon of the ulna
• It inserts onto the pisiform bone and hook of the hamate and the base of the fifth metacarpal bone
• Actions: FCU flexes and adducts at the wrist.
• Innervation: Ulnar nerve (C8-T1 from the medial cord of the brachial plexus).

Question 4

Describe the Palmaris Longus:
• Where does it originate
• Where does it insert
• What is its action
• What is it innervated by

Answer 4

• originates from the common flexor origin on the medial epicondyle of the humerus
• inserts onto the flexor retinaculum of the wrist and the palmar aponeurosis
• Actions: Palmaris longus is a very weak flexor of the wrist. It can therefore be harvested and used for tendon grafting in reconstructive surgery without producing
any functional deficit
• Innervation: Median nerve (C6-T1 from medial and lateral cords of brachial plexus).

Question 5

which muscle in the forearm is absent in 15% of the population?

Answer 5

Palmaris Longus

Question 6

How do you find out if you have a palmaris longus?

Answer 6

To find out if you have a palmaris longus, flex your wrist and oppose your thumb and little finger i.e. bring the fingertips together. You will be able to see the palmaris longus tendon protruding in the midline.

Question 7

Immediately deep to which muscle would you find the median nerve?

Answer 7

palmaris longus

Question 8

Describe the Flexor Carpi Radialis:
• Where does it originate
• Where does it insert
• What is its action
• What is it innervated by

Answer 8

• originates from the common flexor origin on the medial epicondyle of the humerus
• inserts onto the base of the second and third metacarpals
• Actions: FCR flexes and abducts at the wrist.
• Innervation: Median nerve

Question 9

Describe the Pronator Teres:
• Where does it originate
• Where does it insert
• What is its action
• What is it innervated by

Answer 9

• Pronator teres has two origins:
- a humeral head from the common flexor origin on the medial epicondyle of the
humerus
- ulnar head from the coronoid process
of the ulna
• muscle passes laterally to insert onto the mid-shaft of the radius.
• Actions: Pronator teres pronates the forearm.
• Innervation: Median nerve

Question 10

How does the pronator teres contribute to the cubital fossa?

Answer 10

Lateral border of the pronator teres forms the medial border of the cubital fossa

Question 11

Where does the median nerve pass relative to the pronator teres?

Answer 11

The median nerve passes between the two heads of the pronator teres muscle to exit the cubital fossa.

Question 12

What is the intermediate muscle of the forearm?

Answer 12

Flexor digitorum superficialis

Question 13

Describe the Flexor digitorum superficialis:
• Where does it originate
• Where does it insert
• What is its action
• What is it innervated by

Answer 13

• FDS has two sites of origin:
- humeroulnar ‘head’ originates from the common flexor origin on the medial epicondyle of the humerus, the ulnar collateral ligament and the coronoid process of the ulna
- the radial ‘head’ originates from the anterior surface of the radius
• The FDS muscle splits into four tendons at the wrist, which travel through the carpal tunnel and insert onto the base of the middle phalanges of the four fingers.
• Actions: FDS flexes the metacarpophalangeal joints and proximal interphalangeal joints of the four fingers. It also assists with flexion of the wrist.
• Innervation: Median nerve.

Question 14

Does the Flexor digitorum superficialis have two discrete head?

Answer 14

Rather than having two discrete heads, the two sites of origin form a continuous tendinous arch.

Question 15

Why is the FDS a useful landmark?

Answer 15

the median nerve and ulnar artery pass between its two heads to travel deep to its muscle belly

Question 16

What are the deep muscles of the anterior forearm?

Answer 16

• flexor digitorum profundus
• flexor pollicis longus
• pronator quadratus.

Question 17

Describe the Flexor digitorum  Profundus:
• Where does it originate
• Where does it insert
• What is its action
• What is it innervated by

Answer 17

• originates from the 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 and insert onto to the base of the distal phalanges of the four fingers
• Actions: FDP is the only muscle that can flex the distal interphalangeal joints of the fingers. It also flexes the metacarpophalangeal joints and assists flexion of the wrist
• Innervation: The ulnar (medial) half of FDP,
which flexes the little and ring fingers, is
innervated by the ulnar nerve. The radial
(lateral) half of FDP, which flexes the middle and index fingers, is innervated by the anterior interosseous branch of the median nerve.

Question 18

Describe the Flexor digitorum  Profundus:
• Where does it originate
• Where does it insert
• What is its action
• What is it innervated by

Answer 18

• 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 of the thumb.
• Actions: FPL flexes the interphalangeal joint and metacarpophalangeal joint of the
thumb
• Innervation: Anterior interosseous branch of median nerve.

Question 19

Describe the Pronator Quadratus:
• Where does it originate
• Where does it insert
• What is its action
• What is it innervated by

Answer 19

• originates from the anterior surface of the distal ulna
• inserts onto the anterior surface of the distal radius
• Actions: Pronator quadratus pronates the forearm at the radio-ulnar joints.
• Innervation: Anterior interosseous branch of median nerve.

Question 20

Describe the location of the flexor pollicis longus

Answer 20

The flexor pollicis longus (FPL) muscle is on the radial (lateral) side of FDP in the deep layer of muscles of the anterior forearm (

Question 21

Describe the location of the pronator quadratus

Answer 21

Pronator quadratus is a rectangular-shaped muscle, found deep to the tendons of the FDP and FPL

Question 22

What are the roots of the median nerve?

Answer 22

median nerve is formed from the C6 – T1 roots of the brachial plexus via the union of branches of the medial and lateral cords

Question 23

What are the motor functions of the median nerve?

Answer 23

• innervates the flexor and pronator muscles in the anterior compartment of the forearm (except the flexor carpi ulnaris and the ulnar half of the flexor digitorum profundus, which are innervated by the ulnar nerve).
• It also supplies innervation to the thenar muscles and lateral two lumbricals in the hand

Question 24

What are the sensory functions of the median nerve?

Answer 24

• The sensory distribution of the median nerve is small and is confined to the hand.
• The median nerve gives off a palmar cutaneous branch in the forearm which innervates the radial (lateral) aspect of the palm
• and digital cutaneous branches in the hand, which innervate the radial three and a half fingers (including thumb)on the palmar surface of the hand and the dorsum of their respective distal phalanges

Question 25

What is the path of the median nerve?

Answer 25

• After originating from the union of branches of the medial and lateral cords of the brachial plexus in the axilla, the median nerve descends the arm
• Lateral to brachial artery in the proximal arm and then medial to it in the distal arm
• The median nerve enters the anterior compartment of the forearm via the cubital fossa
• 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.
• It passes distally between the flexor digitorum superficialis muscle and the flexor digitorum profundus muscle

Question 26

Which branches of the median nerve innervates which muscles in the anterior forearm?

Answer 26

Directly from median nerve: Superficial and intermediate layer

Anterior interosseous nerve: Deep layer

Question 27

which muscles in the superficial and intermediate layers of the anterior forearm does the median nerve innervate?

Answer 27

Superficial layer: 
• Pronator teres
• flexor carpi radialis
• palmarislongus.
Intermediate layer: 
• Flexor digitorum superficialis

Question 28

Which muscles of the deep layer of the anterior forearm does the anterior interosseous nerve branch of the median nerve innervate?

Answer 28

• Flexor pollicis longus
• pronator quadratus
• the radial (lateral) half of the flexor digitorum profundus(the medial half of the
muscle is innervated by the ulnar nerve).

Question 29

combined, what are the actions of the muscles supplied by the median nerve in the forearm?

Answer 29

In general, these muscles perform pronation of the forearm, flexion of the wrist and flexion of the digits of the hand

Question 30

In the forearm, the median nerve also gives off the palmar cutaneous branch. What does it innervate?

Answer 30

innervates the skin of the lateral palm

Question 31

After giving off the anterior interosseous and palmar cutaneous branches, the median nerve enters the hand via the carpal tunnel, where it terminates by dividing into two branches. What are these branches and what do they innervate?

Answer 31

• Recurrent branch – innervates most of the thenar muscles, with the exception of adductor pollicis and the deep head of flexor pollicis brevis, both of which are supplied by the ulnar nerve.
• Palmar digital branch – innervates the palmar surface and fingertips of the radial (lateral) three and half digits. Also innervates the lateral two lumbrical muscles. These muscles flex the metacarpophalangeal joints and extend the interphalangeal joints of the index and middle fingers.

Question 32

Why is the palmar cutaneous branch not involved in carpal tunnel syndrome?

Answer 32

It passes superficial to the carpal tunnel

Question 33

What are the roots of the ulnar nerve?

Answer 33

ulnar nerve arises from the brachial plexus. It is a continuation of the medial cord, containing fibres from spinal roots C8 and T1

Question 34

What are the motor functions of the ulnar nerve?

Answer 34

The ulnar nerve innervates the intrinsic muscles of the hand (apart from the thenar muscles and lateral two lumbricals). It also innervates two muscles in the forearm: flexor carpi ulnaris and the ulnar (medial) half of flexor digitorum profundus.

Question 35

What are the sensory functions of the ulnar nerve?

Answer 35

The ulnar nerve innervates the palmar and dorsal surfaces of the ulnar (medial) one and a half fingers, and the ulnar aspect of the palm and dorsum of the hand

Question 36

What is the path of the ulnar nerve?

Answer 36

• After arising from the brachial plexus in the axilla, the ulnar nerve descends the
medial aspect of the arm.
• At the 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.
• The ulnar nerve is palpable and vulnerable to injury at the medial epicondyle.
• The ulnar nerve passes between the two heads of the flexor carpi ulnaris (FCU) muscle to enter the forearm, and travels deep to the FCU muscle, adjacent to the
ulna

Question 37

What are the 3 branches of the ulnar nerve in the forearm?

Answer 37

• Muscular branch – innervates flexor carpi ulnaris, which flexes and adducts the wrist, and the ulnar (medial) half of flexor digitorum profundus, which flexes the little and ring fingers
• Palmar cutaneous branch – innervates the ulnar (medial) third of the palm.
• Dorsal cutaneous branch – innervates the dorsal surface of the ulnar (medial) one and a half fingers, and the associated dorsal area of the hand

Question 38

Describe the route of the ulnar nerve from the wrist downwards?

Answer 38

At the wrist, the ulnar nerve travels superficial to the flexor retinaculum and medial to the ulnar artery. It enters the hand via the ulnar canal (Guyon’s canal). In the hand, the ulnar nerve terminates by giving rise to superficial and deep branches

Question 39

Which of the intrinsic muscles of the hand are innervated by the deep branch of the ulnar nerve?

Answer 39

 Hypothenar muscles (a group of muscles associated with the little finger)
 Ulnar (medial) two lumbricals
 Adductor pollicis
 Palmar and dorsal interossei of the hand
 Palmaris brevis
 Deep head of flexor pollicis brevis

Question 40

What is the froment’s sign?

Answer 40

Froment’s sign is a test for ulnar nerve palsy, specifically paralysis of the adductor pollicis:
• The patient is asked to grasp a piece of paper between their thumb and index finger, as the paper is pulled away.
• They should be able to hold the paper there with no difficulty (by adduction of the
thumb).
• A positive test is when 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 pape

Question 41

Where does the superficial bramch of the ulnar nerve arise and what does it innervate?

Answer 41

The superficial branch of the ulnar nerve arises in the palm and innervates the palmar surface of the ulnar (medial) one and a half fingers via the palmar digital nerves

Question 42

What is the musculocutaneous nerve a continuation of?

Answer 42

continuation of the lateral cord of the brachial plexus (C5, C6 and C7) and emerges from the brachial plexus at the inferior border of the pectoralis minor muscle.

Question 43

What are the motor functions of the musculocutaneous nerve?

Answer 43

The musculocutaneous nerve supplies the muscles in the anterior compartment of the arm: coracobrachialis, biceps brachii and
brachialis

Question 44

What are the sensory functions of the musculocutaneous nerve?

Answer 44

After supplying the muscles in the anterior compartment of the arm, the musculocutaneous nerve contains purely sensory fibres and changes its name to the lateral cutaneous nerve of the forearm, which innervates the lateral aspect of the forearm.

Question 45

What is the anatomical course of the musculocutaneous nerve?

Answer 45

• musculocutaneous nerve leaves the axilla and pierces the coracobrachialis muscle near its point of insertion on the humerus.
• It gives a branch to this muscle.
• The musculocutaneous nerve then passes down the flexor compartment of the
arm, superficial to brachialis but deep
to biceps brachii.
• It innervates both of these muscles and
gives articular branches to the elbow.
• The musculocutaneous nerve then pierces the deep fascia lateral to biceps brachii to emerge lateral to the biceps tendon and brachioradialis.
• It continues into the forearm as the lateral cutaneous nerve of the forearm and provides sensory innervation to the lateral aspect of the forearm.
• In this region, it can be found in close proximity to the cephalic vein.

Question 46

Which neural segment do the cutaneous fibres of the musculocutaneous nerve arise from?

Answer 46

the musculocutaneous nerve contains fibres from the C5-7 spinal roots. Its cutaneous distribution is entirely within the C6 dermatome, indicating that those sensory fibres that supply the skin are derived from the C6 neural segment

Question 47

What might be the causes and effects of Injury to the Musculocutaneous Nerve?

Answer 47

• The musculocutaneous nerve is well protected within the axilla, and injury is
uncommon.
• Characteristic mechanisms of injury include penetrating trauma to the axilla (e.g. stabbing), anterior dislocation of the shoulder (which more commonly injures the axillary nerve) and injury during shoulder surgery.
• Motor functions:
- Coracobrachialis, biceps brachii and brachialis muscles are paralysed.
- Flexion at the shoulder and elbow are both weakened but remain possible as a
result of the action of pectoralis major and brachioradialis respectively.
- Supination is weakened but still possible due to the action of supinator.
• Sensory functions:
-There is loss of sensation over the radial (lateral) side of the forearm.

Question 48

Where does the medial cutaneous nerve arm arise from and what is its nerve roots and what is its distribution?

Answer 48

• smallest branch of the brachial plexus, arising from the medial cord, and contains T1 fibres.
• It is distributed to the skin of the distal medial arm, extending as far as the elbow.

Question 49

What does the medial cutaneous nerve of the arm communicate with?

Answer 49

The medial cutaneous nerve of the arm communicates with the intercostobrachial nerve (T2); hence there is some overlap in its distribution with both the T1 and T2 dermatomes.

Question 50

Where does the medial cutaneous nerve forearm arise from and what is its nerve roots and what is its distribution?

Answer 50

The medial cutaneous nerve of the forearm (or medial antebrachial cutaneous nerve) arises from the medial cord of the brachial plexus. It derives its fibers from the C8 and T1 nerves and supplies skin on the distal anterior surface of the arm and the ulnar (medial) side of the forearm, as far distally as the wrist

Question 51

Describe the radial nerve?

Answer 51

The radial nerve is the nerve of the posterior compartment of the arm and forearm. It briefly passes into the anterior compartments at the level of the elbow and
passes through the cubital fossa. In the cubital fossa, it lies between the brachioradialis and brachialis muscles and divides into its deep and superficial branches

Question 52

How are the radial and ulnar arteries formed?

Answer 52

The radial and ulnar arteries are formed by the bifurcation of the brachial artery within the cubital fossa

Question 53

Which part of the forearm does the radial & ulnar artery supply?

Answer 53

Radial - Posterolateral - It contributes to anastomotic networks surrounding the elbow joint and carpal bones.
Ulnar - Anteromedial - It contributes to an anastomotic network surrounding the elbow joint

Question 54

What are the branches of the ulnar artery in the forearm?

Answer 54

anterior and posterior interosseous arteries, which supply deeper structures in the forearm

Question 55

What are the anastamoses of the ulnar and radial artery in the hand called?

Answer 55

the superficial palmar arch, and the deep palmar arch

Question 56

Where can the pulses in the upper limb be felt?

Answer 56

• Brachial pulse: can be palpated in the cubital fossa, immediately medial to the tendon of the biceps brachii - also where korotkoff sounds are heard when measuring BP
• Radial pulse can be palpated at the wrist, immediately radial (lateral) to the prominent tendon of the flexor carpi radialis muscle.
• Ulnar pulse can also be palpated at the wrist, immediately radial (lateral) to the tendon of flexor carpi ulnaris and proximal to the pisiform bone

Question 57

Where is the deep venous system of the upper limb located and what is it formed by?

Answer 57

• The deep venous system of the upper limb is situated deep to the deep fascia.
• It is formed by venae comitantes; these are paired veins which lie either side of an
artery.
• In the upper limb, the deep veins share the name of the artery they accompany.
• The brachial veins are situated either side of the brachial artery. The pulsations of
the brachial artery assist their venous return.
• The radial and ulnar arteries also have
venae comitantes, known as the radial veins and ulnar veins respectively.

Question 58

What runs between the deep and superficial veins of the upper limb?

Answer 58

Perforating veins run between the deep and superficial veins of the upper limb, connecting the two systems.

Question 59

What are the border of the cubital fossa?

Answer 59

 Lateral border: medial border of the brachioradialis muscle.
 Medial border: lateral border of the pronator teres muscle.
 Superior border: hypothetical line between the epicondyles of the humerus

Question 60

What forms the floor and the roof of the cubital fossa?

Answer 60

Floor: proximally by the brachialis, and distally by the supinator muscle

Roof: skin and fascia and is reinforced by the bicipital aponeurosis

Question 61

What is the cubital fossa an important site for?

Answer 61

The cubital fossa is an important site for venepuncture (obtaining blood samples through needle-puncture of a vein)

Question 62

What structures run through the roof of the cubital fossa?

Answer 62

• median cubital vein
• medial cutaneous nerve of the forearm
• lateral cutaneous nerve of the forearm

Question 63

What are the contents of the cubital fossa?

Answer 63

lateral to medial:

• radial nerve
• Biceps tendon
• brachial artery
• median nerve

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Question 64

Describe the contents of the cubital fossa?

Answer 64

 Radial nerve: this lies on the lateral edge of the cubital fossa, between the
brachioradialis and brachialis muscles. It divides into its deep and superficial branches and the deep branch passes between the two heads of supinator to enter the posterior forearm.
 Biceps tendon: this runs through the cubital fossa, inserting onto the radial tuberosity, just distal to the neck of the radius.
 Brachial artery: this supplies oxygenated blood to the forearm. It bifurcates into the radial and ulnar arteries at the apex of the cubital fossa.
 Median nerve: this leaves the cubital fossa by passing between the two heads of the pronator teres.