Axilla and Arm

Question 1

What are the Boundaries of the axilla (in anatomical position)

Answer 1

• Pectoralis major forms the anterior axillary fold
• Latissimus dorsi and teres major form the posterior axillary fold
• An important landmark: the midaxillary line starts at the midpoint of the axilla and runs down the length of the torso

Question 2

Describe the Axillary sheath

Answer 2

-Thick layer of fascia enclosing: axillary artery, axillary vein, & distal portion of brachial plexus

Question 3

Describe the Axillary artery

Answer 3

• Continuation of the subclavian artery (name changes at 1st rib)
• Becomes the brachial artery at inferior border of teres major
• Subdivided based on relationship to pectoralis minor:
• Multiple arterial anastomoses exist around the shoulder. These alternative pathways can maintain blood flow to the UE if the axillary artery becomes occluded.

Question 4

Describe the First Part (one branch) of the Axillary artery

Answer 4

• Proximal to pectoralis minor
• Superior thoracic artery
• supplies 1st-2nd intercostal spaces

Question 5

Describe the Second Part (two branches) of the Axillary artery

Answer 5

• Deep to pectoralis minor
  1) Thoracoacromial artery
• Supplies pectoral muscles and deltoid

2) Lateral thoracic artery:
- supplies serratus anterior and pectoral muscles.
- courses with the long thoracic nerve

Question 6

Describe the Third Part (three branches) of the Axillary artery

Answer 6

-Distal to pectoralis minor

1) Subscapular artery
- Circumflex scapular artery supplies scapular region
- Thoracodorsal artery supplies latissimus dorsi

2) Anterior circumflex humeral artery
- supplies shoulder and arm

3) Posterior circumflex humeral artery
- supplies shoulder and arm
- anastomoses with anterior circumflex humeral artery
- travels with axillary nerve through quadrangular space
- borders of the quadrangular space: teres minor (superior), teres major (inferior), humerus (lateral), and long head of triceps brachii (medial)

Question 7

Describe the Axillary vein

Answer 7

• Formed by union of brachial veins & basilic vein at inferior border of teres major
• Becomes subclavian vein at level of 1st rib
• Major tributaries:
  1) Brachial veins (deep)
  2) Basilic vein (superficial and medial)
  3) Cephalic vein (superficial and lateral)
  4) Additional veins parallel branches of axillary artery

Question 8

Describe the parts of the Brachial Plexus

Answer 8

• Roots
• Trunks
• Divisions
• Cords
• Branches

Question 9

Describe the Roots and their branches

Answer 9

• In the neck
• Ventral rami of C5-T1 spinal nerves

1) Dorsal scapular nerve
- Motor: levator scapulae & rhomboid major and minor
- Travels with dorsal scapular artery, medial to the medial border of the scapula

2) Long thoracic nerve
- Motor: serratus anterior
- Travels with lateral thoracic artery along the midaxillary line, on superficial surface of serratus anterior
- Lesion of the long thoracic nerve results in a “winged scapula” (inability to fix the scapula on the body wall, against the thoracic cage)

Question 10

Describe the Trunks and their branches

Answer 10

-In the neck

1) Superior trunk (C5-C6)
- Suprascapular nerve (C5-6)
- Motor: supraspinatus and infraspinatus
- Travels with suprascapular artery (“Army over Navy”)

2) Middle trunk (C7)
3) Inferior trunk (C8-T1)

Question 11

Describe the Divisions

Answer 11

• Deep to clavicle
• Each trunk gives rise to a posterior and an anterior division
• The anterior divisions give rise to nerves associated with the anterior compartments of the arm and forearm, and the palmar hand
• The posterior divisions give rise to nerves associated with the posterior compartments of the arm and forearm, and the dorsal hand

Question 12

Describe the cords and their branches

Answer 12

• Distal to clavicle
• Named according to their position relative to axillary artery (when the upper extremity is in anatomical position)

1) Lateral cord formed by anterior divisions of superior and middle trunks (C5-C7)
- “LMM” Lateral cord gives rise to Musculocutaneous and Median nerves

2) Medial cord formed by anterior division of inferior trunk (C8-T1)
- “MUM” Medial cord gives rise to Ulnar and Median nerves

3) Posterior cord formed by posterior divisions of all trunks (C5-T1)
- “PAR” Posterior cord gives rise to Axillary and Radial nerves

The terminal branches of the lateral and medial cords form an “M”

Question 13

Describe the branches of the Lateral Cord

Answer 13

1) Musculocutaneous nerve
- Motor: muscles of the anterior compartment of the arm
- Sensory: near the elbow, it terminates as the lateral cutaneous nerve of the forearm which innervates the skin of lateral forearm

2) contributes to the Median nerve
- Motor: most of the muscles of the anterior compartment of the forearm and some intrinsic hand muscles
- Sensory: skin of part of the hand
- Carpal tunnel syndrome involves compression of the median nerve as it passes deep to the flexor retinaculum at the wrist

3) Lateral pectoral nerve
- Motor: pectoralis major
- There may be a communicating branch between the lateral and medial pectoral nerves

Question 14

Describe the branches of the Medial Cord

Answer 14

-contributes to the Median nerve

1) Ulnar nerve
- Motor: 1½ muscles in the anterior forearm, and most intrinsic hand muscles
- Sensory: skin of part of the hand
- Very superficial as it crosses the elbow joint; it can be compressed here (“funny bone”)

2) Medial pectoral nerve
- Motor: pectoralis major and minor

3) Medial cutaneous nerve of the arm
- Sensory: skin of medial arm

4) Medial cutaneous nerve of the forearm
- Sensory: skin of anterior arm and medial forearm

Question 15

Describe the branches of the Posterior Cord

Answer 15

1) Axillary nerve (C5-6)
- Exits axilla posteriorly through the quadrangular space (with posterior circumflex humeral vessels)
- (Structures in quadrangular space are susceptible to damage with a fracture of the surgical neck of the humerus)
- Motor: deltoid and teres minor
- Sensory: skin on the lateral aspect of the shoulder

2) Radial nerve
- Courses in radial groove on posterior aspect of humeral shaft (with deep artery & vein of the arm)
- (Structures in radial groove are susceptible to damage with a midshaft fracture of the humerus)
- Motor: muscles of the posterior arm and forearm
- Sensory: skin of the posterior arm, forearm and hand

3) Upper subscapular nerve
- Motor: subscapularis (superior part)

4) Thoracodorsal nerve
- Motor: latissimus dorsi
- Travels with thoracodorsal artery

5) Lower subscapular nerve
- Motor: subscapularis (inferior part) and teres major

Question 16

Describe Brachial Plexus Injuries

Answer 16

• A major goal of the upper extremity labs is to be able to anticipate the motor and sensory deficits that would result from damage to the brachial plexus and its branches
• Proximal injuries (e.g., roots of the brachial plexus): many compartments affected
• Distal injuries (e.g., terminal branches): fewer compartments affected

Question 17

Describe Damage to the roots of the brachial plexus

Answer 17

• Trend: C5-C6 innervate muscles around the shoulder/arm while C7-C8 innervate muscles in the hand
• Injury to C5-C6: Erb’s palsy; affects shoulder and anterior arm muscles; upper extremity presents in “waiter’s tip” position, with adducted and medially rotated glenohumeral joint and extended elbow joint; affects C5 and C6 dermatomes
• Injury to C8-T1: Klumpke’s palsy; affects intrinsic hand muscles, resulting in a claw hand (full); affects C8 and T1 dermatomes

Question 18

Describe the Muscles of the Anterior Compartment of the Arm and the general rules

Answer 18

1) Coracobrachialis
2) Biceps brachii
3) Brachialis

• Innervation rule: musculocutaneous nerve (C5-7)
• Action rules:Flex glenohumeral or elbow joint + Supinate forearm

Question 19

Describe Origin, insertion, and action of Coracobrachialis

Answer 19

• Origin: coracoid process of scapula
• Insertion: midshaft of anterior humerus
• Action: flex glenohumeral joint

Question 20

Describe Origin, insertion, and action of Biceps brachii

Answer 20

• Origin:
  1) Short head: coracoid process of scapula
  2) Long head: supraglenoid tubercle of scapula; tendon passes through the intertubercular groove to get to the supraglenoid tubercle
• Insertion: radial tuberosity (& fascia of forearm via bicipital aponeurosis)
• Actions: flex elbow joint (when forearm is supinated supinate forearm (when elbow is flexed) weakly flex glenohumeral joint

-Note: the biceps reflex test can be used to assess the musculocutaneous nerve and the C5-C6 spinal segments

Question 21

Describe Origin, insertion, and action of Brachialis

Answer 21

• Origin: distal half of the humerus
• Insertion: ulnar tuberosity
• Action: flex elbow joint

Question 22

Describe the Muscles of the Posterior Compartment of the Arm

Answer 22

• Origin:
  1) Long head- infraglenoid tubercle of scapula
  2) Lateral head- posterior humerus
  3) Medial head- posterior humerus
• Insertion: olecranon process of ulna
• Action: extend elbow joint (& glenohumeral joint via long head)
• Innervation rule: radial nerve (C6-8)

-Note: the triceps reflex test can be used to assess the radial nerve and the C7-C8 spinal segments

Question 23

Describe the Arteries of the Arm

Answer 23

-At inferior border of teres major, axillary artery changes names to become brachial artery

Brachial artery

• Supplies arm
• Blood pressure is typically measured from the brachial artery
• Mid-arm compression of the brachial artery aids in controlling hemorrhage in the distal upper extremity

Gives rise to:

1) deep artery of the arm (profunda brachii artery) is the primary supply of blood to the posterior arm –> it courses in the radial groove of the humerus, with radial nerve (Structures in radial groove are susceptible to damage with a midshaft fracture of the humerus)
2) ulnar collateral arteries (anastomose around elbow joint)

Question 24

Describe the Deep veins of the arm

Answer 24

• Accompany arteries and have the same names (e.g., brachial veins, deep veins of the arm)
• Typically paired
• Communicate with superficial veins

Question 25

1) If there is a blockage in the dorsal scapular artery at its origin from the transverse cervical artery, how could blood still reach the dorsal scapular artery distal to the blockage?

Answer 25

Answer

Question 26

2) If your patient has a severely weakened ability to flex the elbow joint, which nerve is most likely to be damaged? If this same patient also has motor deficits related to the muscles of the anterior forearm and some intrinsic muscles of the hand, which cord of the brachial plexus is most likely to be damaged?

Answer 26

Answer