Part 2 - Axilla, Brachial Plexus & Arm

• Axilla


  • Pyramidal space inferior to glenohumeral joint and superior to the axillary fascia at the junction of the arm and thorax
  • Provides a "distribution center" that is protected by the adducted upper limb for the neurovascular structures serving the upper limb
  • Communicates with posterior triangle of neck

  
• Boundaries of the Axilla

  • Apex
  • Base
  • Anterior
  • Posterior
  • Medial
  • Lateral

  
• Apex of the Axilla


  • Cervico-axillary canal bounded by first rib, clavicle and superior edge of scapula
  • Neurovascular bundles pass through this superior opening

  
• Base of the Axilla

  • Formed by the concave skin, subcutaneous tissue and axillary fascia extending from the arm to the thoracic wall (approx. 4th rib level), forming the axillary fossa (armpit)

  
• Anterior Boundary of the Axilla

  • Pectoralis major and minor, subclavius and clavipectoral fascia
  • Anterior axillary fold: inferior most part of anterior border that may be grasped between the finger, formed by pectoralis major and overlying integument

  
• Posterior Boundary of the Axilla

  • Teres major, latissimus dorsi, subscapularis and scapula
  • Posterior axillary fold: formed by latissimus dorsi, teres major and overlying integument
• Medial Boundary of the Axilla

  • Formed by thoracic wall (1st to 4th ribs and intercostal muscles) and serratus anterior

  
• Lateral Boundary of the Axilla

  • Formed by the intertubercular sulcus in the humerus
• Contents of the Axilla

  • Lateral thoracic vessels
  • Branches of 2nd to 4th intercostal nerves
  • Long thoracic nerve
  • Axillary lymph nodes
  • Fat
  • Medial cutaneous nerve of arm
  • Ulnar nerve
  • Medial cutaneous nerve of forearm
  • Median nerve
  • Medial root of median nerve
  • 3rd part of axillary artery
  • Musculocutaneous nerve
  • Axillary vein
  • Posterior cord
  • Subscapular vessels
  • Axillary nerve
  • Thoracodorsal nerve
  • Upper and lower subscapular nerves
  • Posterior circumflex humeral vessels

  
• Axillary Artery


  Divided into 3 parts relative to the pectoralis minor

  
• Branches of the Axillary Artery

  • First part: Superior thoracic artery
  • Second part: Thoraco-acromial artery, Lateral thoracic artery
  • Third part: Subscapular artery, Anterior circumflex humeral artery, Posterior circumflex humeral artery

  
• Brachial Plexus


  Network of nerves from spinal cord that controls muscle movements and sensation in the upper limb
• Components of the Brachial Plexus


  • Roots
  • Trunks
  • Cords
  • Divisions
  • Branches
• Roots of the Brachial Plexus

  • Between anterior and middle scalene muscles
  • Ventral rami of C5-T1
  • Prefixed: C4-C8 contribute in some cases
  • Postfixed: C6-T2 contribute in some cases

  
• Trunks of the Brachial Plexus

  • Superior trunk: union of C5 and C6
  • Middle trunk: continuation of C7
  • Inferior trunk: union of C8 and T1

  
• Divisions of the Brachial Plexus


  • Behind clavicle
  • Each trunk splits into an anterior and a posterior division
• Cords of the Brachial Plexus

  • Lateral cord: union of anterior divisions of superior and middle trunks
  • Medial cord: anterior division of inferior trunk
  • Posterior cord: union of posterior divisions of superior, middle and inferior trunks

  
• Supraclavicular Branches of the Brachial Plexus

  • From the roots: Dorsal scapular nerve, Long thoracic nerve, Contribution to phrenic nerve, Unnamed muscular nerves
  • From the trunks: Nerve to subclavius, Suprascapular nerve

  
• Infraclavicular Branches of the Brachial Plexus

  • From lateral cord: Lateral pectoral nerve, Musculocutaneous nerve, Lateral head of median nerve
  • From posterior cord: Axillary nerve, Upper subscapular nerve, Thoracodorsal nerve, Lower subscapular nerve, Radial nerve
  • From medial cord: Medial cutaneous nerve of arm, Medial cutaneous nerve of forearm, Medial pectoral nerve, Ulnar nerve, Medial head of median nerve

  
• Medial cord


  Terminal branch (C8,T1)
• Muscles of the anterior forearm compartment

  • Except for flexor carpi ulnaris and ulnar half of flexor digitorum profundus
  • 5 intrinsic muscles in thenar half of palm and palmar skin

  
• Axillary nerve


  • Terminal branch of posterior cord, C5 and C6
  • Glenohumeral joint, teres minor and deltoid, skin of superolateral arm

  
• Upper subscapular nerve


  • Side branch of posterior cord; C5
  • Superior portion of subscapularis

  
• Thoracodorsal nerve


  • Side branch of posterior cord; C6,C7 and C8
  • Latissimus dorsi

  
• Lower subscapular nerve


  • Side branch of posterior cord; C6
  • Inferior portion of subscapularis and teres major
• Radial nerve


  • Larger terminal branch of posterior cord; C5-T1
  • All muscles of posterior compartments of arm and forearm, skin of posterior and inferolateral arm, posterior forearm, dorsum of hand lateral to axial line of digit 4

  
• Medial pectoral nerve


  • Side branches of medial cord; C8 and T1
  • Pectoralis minor and sternocostal head of pectoralis major

  
• Medial cutaneous nerve of arm

  • Side branches of medial cord; C8 and T1
  • Skin of medial side of arm, as far distal as medial epicondyle of humerus and olecranon of ulna

  
• Medial cutaneous nerve of forearm

  • Side branches of medial cord; C8 and T1
  • Skin of medial side of forearm, as far distal as wrist

  
• Ulnar nerve


  • Larger terminal branch of medial cord; C8,T1 and often C7
  • Flexor carpi ulnaris and ulnar half of flexor digitorum profundus, most intrinsic muscles of hand, skin of hand medial to axial line of digit 4

  
• Injuries to the brachial plexus can be caused by falls on side of head/shoulders, traction during forceps delivery, and pressures leading to incomplete injuries
• Cords are rarely damaged by direct injury except gunshots and stab wounds
• Efforts to reduce shoulder dislocation could also produce nerve injuries

  
• Superior trunk injury (Erb-Duchenne paralysis)


  • Upper trunk stretches/tears at Erb's point (C5&C6)
  • Consequence- waiter's tip position (arm hanging extended in medial rotation due to flexors and lateral rotators being paralyzed)
• Inferior trunk injury (Klampke's paralysis)


  • 'Claw hand' deformity
  • Consequence- anesthesia on medial arm and hand surface; paralysis/atrophy of muscles innervated by ulnar nerve

  
• Crutch paralysis


  • Pressure from usage of crutches
  • 'wrist drop' deformity
  • Mainly affects radial and ulnar nerves
• Sleep palsy/'Saturday night palsy'

  • Pressure on radial nerve with subject asleep under influence of alcohol or narcotics
  • Usually temporary
• 'winging of the scapula'


  • Affects long thoracic nerve
  • Winged appearance on back
  • Inability to raise arm or carry out pushing movements

  
• Cervical rib syndrome


  Presence of cervical rib on C7 may put may put pressure on lower trunk
• Biceps brachii


  • Short head- tip of coracoid process of scapula
  • Long head- supraglenoid tubercle of scapula
  • Radial tuberosity and fascia of forearm via bicipital aponeurosis
  • Musculocutaneous nerve (C5,C6,C7)
  • Supinates forearm
  • Flexes forearm when supinated
  • Short head resists dislocation of shoulder