Axilla & Brachial Plexus/Posterior Triangle Neck Flashcards Preview

MSI Module II > Axilla & Brachial Plexus/Posterior Triangle Neck > Flashcards

Flashcards in Axilla & Brachial Plexus/Posterior Triangle Neck Deck (17):

Structures that pass through interscalene triangle of the neck

Interscalene triangle: Small triangular space between the anterior and middle scalene muscles and the first rib

Structures that pass through the interscalene triangle:

  • Roots of the brachial plexus
  •  Subclavian artery
  • **NOT the subclavian vein (which passes anterior to the anterior scalene muscle)

A image thumb

Thoracic Outlet Syndrome (TOS)

TOS is the entrapment of neurovascular structures of the upper limb within the costoclavicular space

Affects subclavian artery and vein and brachial plexus


  • Pain radiating throughout the upper extremity from the point of compression
  • Numbness
  • Weakness
  • Pallor of fingers
  • Sensitivity to cold 

A image thumb

Axillary nerve

Axillary nerve

  • Origin: branches from posterior cord of brachial plexus, receiving fibers from C5, C6
  • Course: exits axillary fossa posteriorly, passing through the quadrangular space with the posterior circumflex humeral artery. Gives rise to the superior lateral brachial cutaneous nerve, then winds around the surgical neck of the humerus deep to the deltoid.
  • Major muscle groups supplied: glenohumeral joint, deltoid, teres minor
  • Injury:  Caused by surgical neck fracture of humerus; anterior dislocation of glenohumeral joint
  • Symptoms: inability to abduct arm to horizontal; loss of skin sensation adjacent to lateral deltoid muscle
  • Test for integrity: abduct arm to horizontal and ask patient to hold position against a downward pull 

A image thumb

Radial nerve

Radial nerve

  • Origin: C5, 6, 7, 8, sometimes T1; posterior cord of brachial plexus
  • Course:  Exits axillary fossa posterior to axillary artery; passes posterior to humerus in radial groove with deep brachial artery, between lateral and medial heads of triceps; perforates lateral intermuscular septum; enters cubital fossa, dividing into superficial (cutaneous) and deep (motor) radial nerves)
  • Major muscle groups supplied: all muscles of posterior compartment of forearm
  • Injury: Caused by midshaft fracture of humerus; poorly fitted crutches; any sustained pressure against posterior humerus
  • Symptoms: inability to extend elbow, wrist (wrist drop), and digits; weakened supination; loss of skin sensation on posterior arm and forearm and lateral aspect of dorsum of hand
  • Test for integrity: ask patient to extend elbow, wrist, and proximal phalanges; assess sensory perception in radial nerve domains

A image thumb

Musculocutaneous nerve

Musculocutaneous nerve

  • Origin: Terminal branch of lateral cord, receiving fibers from C5–C7
  • Course: Exits axilla by piercing coracobrachialis; descends between biceps brachii and brachialis, supplying both; continues as lateral cutaneous nerve of forearm.
  • Major muscle groups supplied: Muscles of anterior compartment of arm (coracobrachialis, biceps brachii and brachialis); skin of lateral aspect of forearm.
  •  Injury: the musculocutaneous nerve can be affected through compression due to hypertrophy or entrapment between the biceps aponeurosis and brachialis fascia or it may be injured through stretch as occurs in dislocations and sometimes in surgery
  • Test for integrity: A discrete sensory disturbance is present on the radial side of the forearm. The biceps reflex is also affected

A image thumb

Median nerve

Median nerve

  • Origin: Lateral root of median nerve is a terminal branch of lateral cord (C6, C7) 
Medial root of median nerve is a terminal branch of medial cord (C8, T1)
  • Course: Lateral and medial roots merge to form median nerve lateral to axillary artery; descends through arm adjacent to brachial artery, with nerve gradually crossing anterior to artery to lie medial to artery in cubital fossa
  • Major muscle groups supplied : Muscles of anterior forearm compartment (except for flexor carpi ulnaris and ulnar half of flexor digitorum profundus), five intrinsic muscles in thenar half of palm and palmar skin
  • Injury /Test for integrity: oppose thumb

A image thumb

Ulnar nerve

Ulnar nerve

  • Origin: Larger terminal branch of medial cord, receiving fibers from C8, T1 and often C7
  • Course: Descends medial arm; passes posterior to medial epicondyle of humerus; then descends ulnar aspect of forearm to hand
  • Major muscle groups supplied : Flexor carpi ulnaris and ulnar half of flexor digitorum profundus (forearm); most intrinsic muscles of hand; skin of hand medial to axial line of digit 4
  • Injury /Test for integrity: 

A image thumb

Trunks of brachial plexus

Superior trunk (C5 & C6)

Middle trunk (C7)

Inferior trunk (C8 & T1)


Cords of brachial plexus 

Lateral cord

Posterior cord

Medial cord


Axillary nerve sensory domain

A image thumb

Radial nerve sensory domain

A image thumb

Musculocutaneous nerve sensory domain

A image thumb

Medial cutaneous nerve of the arm sensory domain

A image thumb

Medial cutaneous nerve of the forearm sensory domain

A image thumb

Median nerve sensory domain

A image thumb

Ulnar nerve sensory domain

A image thumb

Collateral routes of blood around scapula

Suprascapular/dorsal scapular arteries connect to subscapular arteries and reroute blood around an axillary artery blockage

A image thumb