Brachial Plexus B&B

Question 1

brachial plexus derives from which nerve roots?

Answer 1

C5 - T1

upper trunk: C5 - C6
lower trunk: C8 - T1

Question 2

which brachial plexus nerves may be affected by lesions (that are important to know)?

Answer 2

axillary
radial
median
ulnar
musculocutaneous

Question 3

the axillary nerve is an extension of which brachial plexus cord?

Answer 3

posterior cord - branches off the top, which should help you remember it is largely made up of nerve roots C5 and C6

[recall brachial plexus is C5 - T1]

Question 4

which major muscle is innervated by the axillary nerve?

Answer 4

deltoid - abduction from 15 to 90 degrees

Question 5

what occurs from lesion of the axillary nerve?

Answer 5

weakness of deltoid (abduction) and loss of sensation over deltoid (also innervates the skin)

can occur via proximal humerus fracture (elderly patient falls) or dislocated shoulder (anterior displacement of humerus)

Question 6

the radial nerve is an extension of which brachial plexus cord?

Answer 6

posterior cord - receives nerves fibers from all nerve roots of brachial plexus (C5 - T1)

Question 7

which muscles does the radial nerve innervate?

Answer 7

wraps around the humerus and innervates the back of the forearm - therefore, it makes sense that it innervates the extensors of the arm, wrist, fingers

including triceps (extends at elbow), extensor carpi radialis longus, extensor carpi radialis brevis, extensor carpi ulnaris

also makes sense, then, that it provides sensory innervation to the back of the hand/forearm

Question 8

what is the hallmark of a radial nerve lesion?

Answer 8

wrist drop because the radial nerve innervates extensors, and without innervation, the flexors dominant, causing the wrist to be flexed (dropped)

extensors - carpi radialis longus, carpi radialis brevis, carpi ulnaris

flexors - carpi radialis, carpi ulnaris

Question 9

Tricep weakness + wrist drop + sensory loss of the back of the hand/forearm = lesion of which nerve?

Answer 9

radial nerve - wraps around the humerus and innervates the back of the forearm - therefore, it makes sense that it innervates the extensors (thus, wrist drop with lesion) of the arm, wrist, fingers

Question 10

how do the symptoms of radial nerve lesion differ if the injury occurs at the level of the axilla or the level of the radius?

Answer 10

Radial nerve runs adjacent to the humerus in the spiral/radial groove, making it vulnerable to compression against the bone

Axilla level damage causes tricep weakness + wrist drop + sensory loss of the back of the hand and forearm

Radio groove damage spares the triceps and most sensory nerves - weakness of wrist and finger extensors + sensory loss of the dorsal hand

Question 11

From which cord of the brachial plexus is the musculocutaneous nerve derived, and of which nerve roots is it made?

Answer 11

lateral cord, C5 - C7

[innervates biceps and gives sensation to the lateral forearm]

Question 12

this nerve innervates the biceps and gives sensation to the lateral forearm. Which nerve is it, and from which cord of the brachial plexus is it derived?

Answer 12

musculocutaneous nerve, derived from the lateral cord of the brachial plexus (made of C5, C6, C7)

Question 13

What would occur from lesion to the musculocutaneous nerve of the brachial plexus?

Answer 13

innervates biceps, gives sensation to lateral forearm

lesion —> weakness of elbow flexion and sensory loss to lateral forearm

Question 14

which nerve roots make up the upper trunk of the brachial plexus, and what is the consequence of a lesion here? (3)

Answer 14

C5 and C6

lesion —> Erb’s Palsy (upper plexus injury): damage to axillary (deltoid abduction), musculocutaneous (biceps), and suprascapular (infraspinatus internal rotation) nerves

classically caused by birth trauma

Question 15

what is Erb’s Palsy?

Answer 15

aka upper plexus injury: lesion to upper trunk of brachial plexus (made of C5 and C6)

damage to axillary (deltoid abduction), musculocutaneous (biceps), and suprascapular (infraspinatus internal rotation) nerves —> arm is straight, at side, and internally rotated with hand facing out

classically caused by birth trauma

Question 16

after birth, a baby is noted to have their arm straight at their side and internally rotated with their hand facing out. What likely happened during birth?

Answer 16

Erb’s palsy: aka upper plexus injury: lesion to upper trunk of brachial plexus (made of C5 and C6)

damage to axillary (deltoid abduction), musculocutaneous (biceps), and suprascapular (infraspinatus internal rotation) nerves —> arm is straight, at side, and internally rotated with hand facing out

classically caused by birth trauma

Question 17

which nerve roots make up the lower trunk of the brachial plexus, and what is the consequence of a lesion here?

Answer 17

C8 - T1

lesion —> Klumpke palsy (lower plexus injury): damage to ulnar and medium nerves (supply intrinsic hand muscles) —> clawed hand

flexors at wrist/arm spared because of dual innervation from upper nerve roots

caused by excessive arm abduction (falling from a tree and catching a branch)

Question 18

what is Klumpke Palsy?

Answer 18

aka lower plexus injury of brachial plexus: lesion to C8-T1 —> damage to ulnar and medium nerves (supply intrinsic hand muscles) —> clawed hand

flexors at wrist/arm spared because of dual innervation from upper nerve roots

caused by excessive arm abduction (falling from a tree and catching a branch)

Question 19

A young girl is taken to the ED by her mother, who says she fell out of a tree while climbing and caught a branch on the way down. Upon examination, her hand appears clawed, but she is able to flex her wrist. What likely happened?

Answer 19

Klumpke palsy (lower plexus injury, C8-T1): damage to ulnar and medium nerves (supply intrinsic hand muscles) —> clawed hand

flexors at wrist/arm spared because of dual innervation from upper nerve roots

caused by excessive arm abduction (falling from a tree and catching a branch)

Question 20

What causes thoracic outlet syndrome?

Answer 20

compression of nerves or vessels leaving the thorax between the first rib and the clavicle (“thoracic outlet”)

occurs in the scalene triangle, bordered by anterior and middle scalene, and above the first rib

Question 21

What kind of anatomical anomaly predisposes an individual to thoracic outlet syndrome?

Answer 21

cervical rib: extra rib from the 7th cervical vertebrae (usually starts at T1)

thoracic outlet syndrome: compression of nerves or vessels leaving the thorax between the first rib and the clavicle (“thoracic outlet”)

Question 22

What are the clinical features of thoracic outlet syndrome? (3)

Answer 22

compression of nerves or vessels leaving the thorax between the first rib and the clavicle (“thoracic outlet”)

1. compression of brachial plexus —> Klumpke palsy (lower plexus injury, worse with arm elevation)
2. compression of veins —> arm swelling
3. arterial compression (rare) —> hand ischemia, lower systolic BP, weak distal pulses

Question 23

in a patient with a brachial plexus injury and also evidence of vascular compromise, such as arm swelling or hand ischemia, you should recognize what?

Answer 23

thoracic outlet syndrome: compression of nerves or vessels leaving the thorax between the first rib and the clavicle (“thoracic outlet”)

1. compression of brachial plexus —> Klumpke palsy (lower plexus injury, worse with arm elevation)
2. compression of veins —> arm swelling
3. arterial compression (rare) —> hand ischemia, lower systolic BP, weak distal pulses

Question 24

where does the long thoracic nerve come off the brachial plexus and what does it innervate?

Answer 24

Branches very early - made of C5, C6, and C7

innervates serratus anterior muscle, which pulls scapula against rib cage

lesion —> “winged” scapula (sticks out)

Question 25

A patient comes into the office with a trauma injury. You ask them to press their outstretched arm against the wall, and you notice their scapula sticks out when they do so (“winged”). What is the likely cause?

Answer 25

lesion of long thoracic nerve: branches very early - made of C5, C6, and C7

innervates serratus anterior muscle, which pulls scapula against rib cage