Brachial Plexus

Question 1

What is the generic route of the brachial plexus?

Answer 1

1. Runs from ventral rami of C5-T1 spinal roots emerging between anterior (attaches to rib 1) and medial scalene muscles (sits posterior of the anterior one) with the subclavian artery anterior
2. Posterior neck triangle
3. Mid point of clavicle and posteriorly
4. Descends inferiorly and laterally to reach the upper limb running with and wrapping round the axillary artery

Question 2

What is the point of having a plexus?

Answer 2

Nerves grow into the anterior and posterior condensations of mesoderm in the limb which means damage to a spinal nerve wont leave the entire limb paralysed

Question 3

What muscle is just below the clavicle?

Answer 3

Subclavius

Question 4

What occurs at the carotid artery bifurcation?

Answer 4

Baroreceptors present then artery splits into external and internal carotid arteries

Question 5

What forms the posterior and anterior axillary folds?

Answer 5

Anterior: pectoralis major and minor

Posterior: latissimus dorsi and teres major

Question 6

What is the axilla region? What does it contain?

Answer 6

Region superior to armpit connecting the neck to the upper limb bordered by pectoral girdle muscles and thoracic cage filled with fat with a tail of the breast extending into this region - it contains Neurovasculature of the upper limb (axillary artery and plexus sits in axillary sheath) and important lymph node groups

Question 7

What can removal of lymph nodes lead to?

Answer 7

Lymphoedema

Question 8

What areas do the axillary lymph nodes drain?

Answer 8

Anterior thoracic wall and breast
Posterior thoracic wall
Upper limb

Question 9

Where can you palpate the subclavian artery?

Answer 9

Posterior to medial clavicle

Question 10

What does the circumflex humoral run with and where is it?

Answer 10

Runs with axillary nerve + 5cm inferior to acromion

Question 11

Describe the structure of brachial plexus from the neck to the upper limb.

Answer 11

1. Roots (Rats): C5-T1 (C4 and T2 can sometimes be involved)
2. Trunks (That): Upper (U), Medial (M) and Lower (L)
3. Divisions (Do): anterior + posterior branch from each of the 3 trunks
4. Cords (Cartwheels): lateral (2 x A from U and M), posterior (3 x P from U, M and L) and medial (A from L) in relation to axillary artery
5. Branches (Badly):
   - Lateralt -> musculocutaneous and median
   - Posterior -> radial and axillary
   - Medial -> median and ulnar

Question 12

How can the musculocutaneous nerve be damaged? What is the consequence?

Answer 12

MoA: Direct damage is rare unless there is penetrating injury because its well protected by regional musculature

Consequence: Weakness/loss and paraesthesia/LOS of anterior arm compartment muscles so flexion of shoulder/elbow and supination of forearm (biceps brachii)

Question 13

How can the axillary nerve be damaged? What is the consequence?

Answer 13

MoA: Dislocation of shoulder or # of surgical neck of humerus

Consequence: Weakness/loss and paraesthesia/LOS of deltoid muscles and teres minor

Question 14

How can the median nerve be damaged? What is the consequence?

Answer 14

MoA: Stab or laceration to medial arm, anterior wrist or in tarsal tunnel

Consequence: Weakness/loss and paraesthesia/LOS of most anterior compartment forearm muscles, thenar muscles (base of thumb on palmar side of hand) and lumbricals 1 and 2 (go to 2nd and 3rd digit) i.e. intrinsic hand muscles

Question 15

How can the radial nerve be damaged? What is the consequence?

Answer 15

MoA: # of humeral shaft through spiral groove, # of head/neck of radius, dislocation of head of radius from radio-ulna joint or compression at axillary region as posterior interosseous branch will be injured

Consequence: Weakness/loss and paraesthesia/LOS of posterior arm and posterior forearm compartment muscles

Question 16

How can the ulna nerve be damaged? What is the consequence?

Answer 16

MoA: # of medial humeral epicondyle or injury to anterior wrist

Consequence: Weakness/loss and paraesthesia/LOS of most small intrinsic muscles of the hand

Question 17

What are the 3 legs of the characteristic M seen of the brachial plexus in dissections?

Answer 17

Upper: Musculocutaneous
Medial: Median
Lower: Ulna

Question 18

What nerve comes off of the posterior cord behind the axillary artery?

Answer 18

Axillary n.

Question 19

What are the spinal root values of the nerves of the brachial plexus?

Answer 19

Musculocutaneous (C5-7)
Axillary (C5-6)
Median (C5-T1)
Radial (C5-T1)
Ulnar (C8-T1)

Question 20

How can you damage the C5 root and upper brachial trunk?

Answer 20

Penetrating neck injury

Question 21

If you could open an interval between the long and lateral tricep muscle heads, what would you see?

Answer 21

Radial nerve in the spiral groove on the back of the humerus

Question 22

What are the smaller nerves of the brachial plexus formed by spinal nerves C5-6 primarily? What would happen if they was lost?

Answer 22

1. Lateral pectoral: loss of clavicular head of pectoralis major
2. Suprascapular: supraspinatus and infraspinatus (rotator cuffs) would be lost so shoulder lateral rotation and stability would be compromised
3. Dorsal scapula: rhomboid function would be lost and levator scapulae would be affected too

Question 23

How could the T1 root of the brachial plexus become compromised? What would be the consequence?

Answer 23

Sits superficial in thoracic cavity so is susceptible when there is lung apex pathology e.g. Pancoast tumour - most nerves end up in hand with ulna and radial n. so one of the first signs of a Pancoast tumour may be wasting of small hand muscles where the patient cannot perform dextrous movements with hands as well anymore

Question 24

What is the nerve root of long thoracic nerve? What does it innervate and what would be the mechanism and consequence of damage?

Answer 24

Long thoracic n. (C5-7) supplies the serratus anterior and is vulnerable to damage stab injuries or interventions in the axillary region such as thoracostomy/thoracotomy if incision is too far posterior in the axillary region causing scapula ‘wings’

Question 25

What does the medial pectoral nerve innervate?

Answer 25

Sternal head of pectoralis major and pectoralis minor

Question 26

What does the upper subscapular nerve supply?

Answer 26

Subscapularis

Question 27

What does the thoracodorsal nerve supply?

Answer 27

Latissimus dorsi

Question 28

What does the lower subscapular nerve supply?

Answer 28

Subscapularis and teres major

Question 29

What does the medial cutaneous nerves of the arm and forearm do?

Answer 29

Skin sensation

Question 30

What is the large vein that sits near axillary artery that can be cannulated?

Answer 30

Axillary vein (will show dilations where valves are)

Question 31

What muscle does the musculocutaneous nerve run through?

Answer 31

Coracobrachialis

Question 32

Give the spinal root values of the muscles innervated by the radial nerve (C5-T1).

Answer 32

Brachioradialis (elbow flexor), radial wrist extenson and posterolateral dermatomes: C5-6

Triceps and digit extensors: C7-8

Question 33

What are the borders of posterior triangle of the neck? What is palpable here?

Answer 33

1. SCM
2. Trapezius
3. Clavicle

Upper part (C5-6) of brachial plexus

Question 34

Why do limbs take on a different resting position when parts of the brachial plexus are damaged? Give an example.

Answer 34

Muscles innervated by the damaged part of the brachial plexus become weakened and waste whilst the remaining functional muscle groups pull the limb into a different resting position e.g. if the forearm supinators are lost via C5-6 loss, the pronator muscles will be unopposed leading to resting pronation of the forearm

Question 35

What is Erb’s palsy?

Answer 35

C5-6 upper root/trunk damage of brachial plexus by forced separation of neck from shoulder via trauma (landing on shoulder), child-birth or stab wounds/lacerations that either stretch the roots or avulse them completely. This results in ‘waiters tip’ appearance of upper limb where the limb is medially rotated due to loss of lateral rotators, pronation due to loss of supinators and the limb hangs limp. The deltoid muscle will be wasted due to axillary nerve loss.

Question 36

What is Klumpke’s palsy?

Answer 36

C8-T1 lower root damage/compression of the brachial plexus causing either stretch or complete avulsion as a result of upward traction of upper limb, cancer at lung apex (e.g. Pancoast tumour) or compression via a cervical rib. This will cause a claw hand deformity where the metacarpophalangeal joints (knuckles) are extended and interphalangeal joints are flexed constantly.