The Axilla and Brachial Plexus

Question 1

What are the boundaries of the axilla

Answer 1

• Four walls
• Floor/Base
• One axillary inlet

Question 2

What are the boundaries of the axillary inlet

Answer 2

Axillary inlet
* Lateral margin of Rib I
* Clavicle
* Superior margin of the scapula
* Completely defined by bones
* Continuous with neck

Question 3

What are the boundaries of the anterior wall

Answer 3

Anterior wall
* Pectoralis major and minor
muscles
* Subclavius muscle
* Clavipectoral fascia
* Lower margin of pectoralis major
= anterior axillary fold

Question 4

What are the boundaries of the medial wall

Answer 4

Medial wall
* Thoracic wall (ribs, intercostal
muscles
* Serratus anterior muscles
* Long throracic nerve and
intercostobrachial nerve

Question 5

What is the floor/base boundary?

Answer 5

Skin of armpit

Question 6

What are the boundaries of the lateral wall

Answer 6

Intertubercular
sulcus of humerus

Question 7

What are the boundaries of the posterior wall

Answer 7

• Posterior wall
• Subscapularis muscle
• Teres major muscle
• Latissimus dorsi muscle
• Long head of triceps
• Latissimus dorsi and teres major =
  posterior axillary fold

Question 8

What are the gateways in the posterior wall and what goes through them

Answer 8

Suprascapular foramen
Suprascapular nerve (through)
Suprascapular artery (ABOVE)

Quadrangular space
Axillary nerve
Posterior humeral circumflex artery

Triangular space
Circumflex scapular artery

Triangular interval
Radial nerve
Profunda brachii artery

Question 9

Biceps Brachi (OIAN)

Answer 9

Biceps brachii
* Origin – two heads,
supraglenoid tubercle (long)
and coracoid process (short)
* Insertion – radial tuberosity
of forearm
* Innervation –
musculocutaneous nerve
(C5, C6)
* Action – flexor of forearm
(strong) and arm (accessory)

Question 10

Branches of axillary artery

Answer 10

3 parts delimited by pectoralis
minor:
1st part : 1 branch
1st part : 1 branch
- Superior thoracic artery
-Upper medial and anterior
axillary walls

2nd part : 2 branches
- Thoracoacromial artery/trunk
-Clavicular, acromial, deltoid,
pectoral branches
-“Cadavers Are Dead People”
- Lateral thoracic artery
-Pectoralis minor, serratus anterior,
lateral thoracic wall

3rd part : 3 branches
Subscapular artery
- Circumflex scapular artery
- Thoracodorsal artery
- Anterior humeral circumflex
artery
- Posterior humeral circumflex
artery

Question 11

What is the arterial supply to shoulders

Answer 11

Subclavian-axillary anastomoses
from subclavian:
thyrocervical trunk
suprascapular a.
circumflex scapular a.
subscapular a.
axillary a.*
posterior circumf. hum. a.
axillary a.*
transverse cervical a.
dorsal scapular a.
circumflex scapular a.
subscapular a.
axillary a.*
from axillary
humeral circumflex aa. (anterior
and posterior.)
thoracoacromial trunk
Axillary-axillary anastomosis
between humeral circumflex aa. and
with profunda brachii a.

Question 12

Describe axillary veins

Answer 12

Axillary vein
* Anteromedial to axillary
artery
* Cephalic vein in
deltopectoral groove

Question 13

Describe axillary lymphatic drainage

Answer 13

Axillary lymph nodes drain the entire upper
limb as well as adjacent areas of the back
and chest
* 5 groups of nodes – lateral (humeral),
pectoral, subscapular, central and apical

Question 14

What are the nerves in the axilla

Answer 14

BRACHIAL PLEXUS
- Ventral rami of C5-T1
Somatic plexus that provides all
somatic motor and sensory
innervation to upper limb (except to
trapezius and patch of skin near the
axilla)

Carry sympathetics to blood vessels,
erector pili muscles, and sweat glands
from T2-T6
No parasympathetic innervation in
upper limbs

Question 15

Describe sections of the brachial plexus

Answer 15

Read That Damn Cadaver Book

The ‘roots’ refer the anterior rami of the spinal nerves that comprise the brachial plexus. These are the anterior rami of spinal nerves C5, C6, C7, C8, and T1.

At each vertebral level, paired spinal nerves arise. They leave the spinal cord via the intervertebral foramina of the vertebral column.

Each spinal nerve then divides into an anterior and a posterior ramus. The roots of the brachial plexus are formed by the anterior rami of spinal nerves C5-T1 (the posterior divisions innervate the skin and musculature of the intrinsic back muscles).

After their formation, these nerves pass between the anterior and medial scalene muscles to enter the base of the neck.

At the base of the neck, the roots of the brachial plexus converge to form three trunks. These structures are named by their relative anatomical location:

Superior trunk – a combination of C5 and C6 roots.
Middle trunk – continuation of C7.
Inferior trunk – combination of C8 and T1 roots.
The trunks traverse laterally, crossing the posterior triangle of the neck.

Divisions
Each trunk divides into two branches within the posterior triangle of the neck. One division moves anteriorly (toward the front of the body) and the other posteriorly (towards the back of the body). Thus, they are known as the anterior and posterior divisions.

We now have three anterior and three posterior nerve fibres. These divisions leave the posterior triangle and pass into the axilla. They recombine into the cords of the brachial plexus.

Cords
Once the anterior and posterior divisions have entered the axilla, they combine together to form three cords, named by their position relative to the axillary artery.

The lateral cord is formed by:

The anterior division of the superior trunk
The anterior division of the middle trunk
The posterior cord is formed by:

The posterior division of the superior trunk
The posterior division of the middle trunk
The posterior division of the inferior trunk
The medial cord is formed by:

The anterior division of the inferior trunk.
The cords give rise to the major branches of the brachial plexus.

Question 16

Describe the major terminal nerves of the brachial plexus

Answer 16

Musculocutaneous Nerve
See more detailed information here.

Roots: C5, C6, C7.
Motor Functions: Innervates the brachialis, biceps brachii and coracobrachialis muscles.
Sensory Functions: Gives off the lateral cutaneous branch of the forearm, which innervates the lateral half of the anterior forearm, and a small lateral portion of the posterior forearm.

Axillary Nerve
See more detailed information here.

Roots: C5 and C6.
Motor Functions: Innervates the teres minor and deltoid muscles.
Sensory Functions: Gives off the superior lateral cutaneous nerve of arm, which innervates the inferior region of the deltoid (“regimental badge area”).

Radial Nerve
See more detailed information here.

Roots: C5 – T1.
Motor Functions: Innervates the triceps brachii, and the muscles in the posterior compartment of the forearm (which are primarily, but not exclusively, extensors of the wrist and fingers).
Sensory Functions: Innervates the posterior aspect of the arm and forearm, and the posterolateral aspect of the hand.

MEDIAN NERVE:
Roots: C6 – T1. (Also contains fibres from C5 in some individuals).
Motor Functions: Innervates most of the flexor muscles in the forearm, the thenar muscles, and the two lateral lumbricals associated with the index and middle fingers.
Sensory Functions: Gives off the palmar cutaneous branch, which innervates the lateral part of the palm, and the digital cutaneous branch, which innervates the lateral three and a half fingers on the anterior (palmar) surface of the hand.

Ulnar Nerve
See more detailed information here

Roots: C8 and T1.
Motor Functions: Innervates the muscles of the hand (apart from the thenar muscles and two lateral lumbricals), flexor carpi ulnaris and medial half of flexor digitorum profundus.
Sensory Functions: Innervates the anterior and posterior surfaces of the medial one and half fingers, and associated palm area.

Question 17

What is a dermatome and peripheral nerve

Answer 17

Dermatome = an area of skin supplied by a single spinal cord level
* Peripheral nerve = can have contributions from multiple spinal levels

Dermatomes overlap; but usually there is an area of MINIMAL overlap. Testing
touch in these area can be used to localize injuries to a specific spinal nerve level.

Pinching the index finger tests
the median (peripheral) nerve
AND C7 spinal nerve level
(dermatome)

Question 18

What are the upper limb dermatomes

Answer 18

Caudal segments extant further distally than cranial segments
* Dermatome patterns change during growth
* Dermatomes can be traced down the lateral aspect of the limb
and back up the medial aspect
* There is considerable overlap; areas of minimal overlap are used
to test for sensation

Areas of minimal overlap are
used for testing:
* C5 – upper lateral arm
* C6 – Pad of thumb (I)
* C7 – Pad of index finger (II)
* C8 – Pad of little finger (V)
* T1 – Medial elbow
* Ventral axial line separates C3-C6
from C8-T2

Question 19

What is Erb’s Palsy

Answer 19

Damage to roots of C5 and C6
* Traumatic lateral neck bending (childbirth, fall on shoulder)
* Involves suprascapular, axillary, dorsal scapular, musculocutaneous, radial (some)
* Supra- and infraspinatus, deltoid, teres minor, biceps, brachialis
* Adducted and medially rotated arm, extended elbow, pronated forearm,
“Waiter’s tip” position of fingers

hand bending back

Question 20

What is Klumpke’s Palsy

Answer 20

• Damage to root of C8 and T1
• Traumatic hyperabduction of arm
• Paralyses most intrinsic hand muscles.
• Claw hand presentation – no 4th and 5th interphalangeal
  extension

happens when you hang off branch

Question 21

Describe radial nerve damage clinical manifestation

Answer 21

• Damage to posterior cord or radial nerve
• Fracture of humerus, Saturday night palsy, improper use of crutches
• Loss of extensors (triceps, brachioradialis, supinator and extensors of
  wrist and fingers) – wrist drop
• Loss of sensation on posterior forearm, elbow and dorsum of hand

wrist drop

Question 22

Describe the clinical manifestation of damage to the median nerve

Answer 22

Damage to median nerve
* Loss of finger and wrist flexors, thenar muscles, and 1st and 2nd
lumbricals
* Cannot flex distal IP joints on digits 2 and 3 – benediction hand
or Pope’s blessing when attempting to make a fist