Nerve injuries and consequences in the upper limb

Question 1

Draw the brachial plexus.

Answer 1

Remember: proximal to distal on the posterior branch = upper subscapular  thoracodorsal  lower subscapular
Proximal to distal on the medial branch = medial pectoral  medial cutaneous nerve of the ARM  medial cutaneous nerve of the FOREARM

Question 2

Name the supraclavicular branches of the brachial plexus and state which muscles they innervate.

Answer 2

Dorsal scapular nerve – rhomboids + levator scapulae (+C34)
Long-thoracic nerve - serratus anterior
Supraclavicular nerve – supraspinatus + infraspinatus
Subclavian nerve - subclavius

Question 3

Name the infraclavicular branches of the brachial plexus and state the muscles that they innervate.

Answer 3

Lateral pectoral nerve – pectoralis major
Thoracodorsal nerve – latissimus dorsi
Upper subscapular nerve – subscapularis (and the lower subscapular nerve)
Lower subscapular nerve – teres major
Medial pectoral nerve – pectoralis minor and pectoralis major
Medial cutaneous nerve of the arm – sensory to medial part of the arm
Medial cutaneous nerve of the forearm – sensory to medial part of forearm

Question 4

Name the terminal branches of the brachial plexus and state the muscles that they innervate.

Answer 4

Musculocutaneous – anterior compartment of arm
Axillary – deltoid + teres minor
Radial – posterior compartment of arm and forearm
Median – most anterior forearm muscles + thenar muscles + lumbricals 1+2
Ulnar – flexor carpi ulnaris + ulnar half of flexor digitorum profundus + all intrinsic hand muscles (except those innervated by the median)

Question 5

The cords of the brachial plexus are named because of their position relative to what important structure?

Answer 5

Axillary artery

Question 6

Which spinal nerves make up each of the following nerves:
Dorsal scapular
Long Thoracic
Suprascapular 
Subclavian 
Lateral Pectoral
Medial Pectoral
Upper Subscapular 
Lower Subscapular 
Lower Subscapular
Axillary 
Musculocutaneous
Radial
Median
Ulnar

Answer 6

Dorsal Scapular- C5
Long Thoracic- C567
Suprascapular - C56 (+C4)
Subclavian - C56 (+C4)
Lateral Pectoral- C567
Medial Pectoral- C8T1
Upper Subscapular- C56
Lower Subscapular- C56, C678
Axillary- C56
Musculocutaneous- C567
Radial- C5678T1
Median- C678T1
Ulnar- C8T1

Question 7

Which two muscles, which start outside the hand, does the ulnar nerve innervate?

Answer 7

Flexor carpi ulnaris (FCU)

Ulnar half of flexor digitorum profundus (FDP)

Question 8

Which nerves supply the shoulder girdle muscles?

Answer 8

C3-C7

Question 9

Which nerves supply the shoulder muscles and elbow joint flexors?

Answer 9

C5+C6

Question 10

Which nerves supply the elbow extensors?

Answer 10

C7+C8

Question 11

Which nerves are responsible for coarse wrist and hand movements?

Answer 11

C6-C8

Question 12

Which nerves supply small muscles of the hand (fine movements)?

Answer 12

C8+T1

Question 13

Describe the dermatome pattern of the skin on the posterior of the upper limb?

Answer 13

They are in strips going from C6-C8 from top to bottom

Question 14

Describe the dermatome pattern of the skin on the anterior of the upper limb?

Answer 14

Same as the posterior side but there are dermatomes of C5 and T1 running down the middle with their apex at the wrist

Question 15

Why is the dermatome pattern different to the cutaneous nerve pattern?

Answer 15

A dermatome is the area of skin innervated by a single spinal nerve
A cutaneous nerve pattern is the area of skin innervated by a peripheral nerve
As the peripheral nerves contain various spinal nerve root fibres, the cutaneous nerve pattern is very patchy compared to the dermatome pattern.

Question 16

What is the benefit of having a brachial plexus instead of having spinal nerves directly innervating the upper limb muscles?

Answer 16

If a muscle group is innervated by one nerve root, damage to that nerve root will cause total loss of function of the muscle. If it is innervated by more than one nerve root then there may still be some function.

Question 17

What does the axillary nerve supply and what branch of the axillary nerve is responsible for sensory innervation of the skin of the regimental badge area?

Answer 17

Deltoid + teres minor

Superior lateral cutaneous branch

Question 18

How is the axillary nerve commonly damaged?

Answer 18

Shoulder dislocation

Question 19

What are the consequences of axillary nerve damage?

Answer 19

Loss of function of deltoid

Anaesthesia or parasthesia of the regimental badge area

Question 20

How can you check to see whether the axillary nerve has been damaged in a shoulder dislocation?

Answer 20

Check for anaesthesia or parasthesia in the regimental badge area

Question 21

Describe the passage of the radial nerve through the arm.

Answer 21

Exits the axilla posterior to the axillary artery
Passes posterior to the humerus in the radial groove, with the deep brachial artery between the medial and lateral heads of triceps
Perforates the lateral intermuscular septum
Enters the cubital fossa
Divides into superficial radial nerve (sensory) and posterior interosseous nerve (motor)

Question 22

How is the radial nerve commonly damaged?

Answer 22

Fractures of the humerus – because the radial nerve is closely associated with the humerus in the radial groove

Question 23

What are the consequences of radial nerve damage?

Answer 23

Wrist drop
Anaesthesia of the dorsal palm (on the thumb side)
Wasting of posterior compartment muscles of arm and forearm

Question 24

What is the most important outcome in radial nerve injury and how does it happen?

Answer 24

Loss of the power grip
To accommodate for extension, the flexors of the fingers are slightly longer than they need to be.
So extension of the wrist allows shortening of the flexors to maximise their efficiency and allow the power grip
With radial nerve palsy, you can’t extend the wrist anymore so you can’t perform the power grip

Question 25

Describe the passage of the musculocutaneous nerve down the arm.

Answer 25

Exits axilla by piercing coracobrachialis
Descends between biceps brachii and brachialis, supplying both
Continues as the lateral cutaneous nerve of the forearm

Question 26

When can the musculocutaneous nerve be damaged?

Answer 26

It isn’t often damaged by trauma because it is well protected by the anterior compartment muscles
It can be cut during surgery for breast cancer

Question 27

Describe the passage of the ulnar nerve down the arm.

Answer 27

Descends in the medial arm
Passes posterior to the medial epicondyle
Descends down the ulnar aspect of the forearm to the hand

Question 28

What are two common sites of damage of the ulnar nerve?

Answer 28

Injury to the medial epicondyle of the humerus

Injury to the wrist

Question 29

What situation commonly encountered by clinicians could cause injury at the wrist?

Answer 29

Self-harm and attempted suicide

Question 30

Which muscles do the ulnar nerve innervate?

Answer 30

Flexor carpi ulnaris (FCU)
Ulnar half of flexor digitorum profundus (FDP)
All the intrinsic hand muscles except LOAF (lumbricals 1+2, opponens pollicis, abductor pollicis brevis, flexor pollicis brevis)

Question 31

Describe and explain the appearance of the hand in ulnar nerve injury.

Answer 31

Damage to the ulnar nerve causes loss of function of lumbricals 3+4
Lumbricals are responsible for flexion of the MCPs and extension of the IPJs
Loss of lumbrical function will cause flexion of the IPJs and extension of the MCPs
The hand has a half claw-like appearance (ring finger and little finger are flexed)

Question 32

What is the ulnar paradox? What causes it?

Answer 32

The claw is worse when the lesion is at the wrist than at the elbow
This is because the lesion at the elbow will mean that the ulnar nerve to both FDP (which causes flexion of the fingers) and the lumbricals (which cause extension of the fingers) will not be functioning meaning you get less flexion of the fingers
With a wrist lesion, the FDP is still functioning and able to cause flexion whereas the lumbricals are not functioning and can’t cause extension
So with wrist lesions you get an unopposed flexion of the fingers due to FDP, meaning that the flexion of the fingers is worse
‘the closer to the paw, the worse the claw’

Question 33

Describe the path of the median nerve down the arm.

Answer 33

The lateral and medial cords merge to form the median nerve, lateral to the axillary artery
It descends through the arm adjacent to the brachial artery with the nerve gradually crossing anterior to the artery to lie medial to the artery in the cubital fossa

Question 34

Which muscles do the median nerve supply?

Answer 34

All the anterior compartment of the forearm muscles except FCU and the ulnar half of FDP
Thenar muscles and lumbricals 1+2

Question 35

What are the contents of the carpal tunnel?

Answer 35

Median nerve
Flexor pollicis longus (FPL)
4 tendons of flexor digitorum superficialis (FDS)
4 tendons of flexor digitorum profundus (FDP)

Question 36

Describe the sensory innervation of the palmar surface of the hand.

Answer 36

Ulnar Nerve = little finger + ½ of ring finger
Median Nerve = ½ of ring finger + middle finger + index finger + ½ of thumb
Radial Nerve = small part of lateral side of thumb

Question 37

What branch comes off the ulnar nerve before it enters the carpal tunnel?

Answer 37

Palmar cutaneous branch
NOTE: this branches off the ulnar nerve before the carpal tunnel and so sensation to the thenar eminence is spared in carpal tunnel syndrome

Question 38

Describe the appearance of a hand in long-term carpal tunnel syndrome.

Answer 38

The thenar eminence will be wasted

There will be a small triangle of muscle that is still prominent – adductor pollicis (it is supplied by the ulnar nerve)

Question 39

What are the consequences of carpal tunnel syndrome?

Answer 39

Loss of fine movement in the lateral digits (thumb, index finger and middle finger)

Question 40

What are the consequences of injury to the long-thoracic nerve?

Answer 40

Winging of the scapula

This is due to loss of function of serratus anterior

Question 41

What is Erb-Duchenne Palsy and what can it be caused by?

Answer 41

Damage to the upper roots (C5, C6)

It can be caused by over-abduction of the neck (e.g. when falling on your neck or delivering a baby)

Question 42

Describe the appearance of a patient with Erb-Duchenne Palsy.

Answer 42

They arm is pronated and their wrist is flexed – ‘waiter’s tip’

Question 43

Why is the arm pronated in Erb-Duchenne Palsy?

Answer 43

C5 and C6 are part of the musculocutaneous nerve, which innervates biceps brachii
The lack of biceps supination causes the forearm to pronate
NOTE: many muscles are affected – shoulder and anterior arm

Question 44

What is the name given to lower nerve root injury and what is it caused by?

Answer 44

Klumpke’s Palsy

It can be caused by over-abduction of the arm due to gripping overhead to break a fall

Question 45

Which nerves are usually affected in lower nerve root injury?

Answer 45

T1 (and sometimes C8)

Question 46

Which muscles does T1 innervate?

Answer 46

T1 mainly supplies the small muscles of the hand via the median and ulnar nerves so there is a loss of activity in many of the hand muscles

Question 47

What are the consequences of Klumpke’s Palsy?

Answer 47

The whole hand is clawed
This is due to loss of activity of the lumbricals – you get reduced extension of the IPJs and reduced flexion of the MCP joints