Shoulder, Axilla, Brachial Plexus

Question 1

Shoulder

Answer 1

• Shoulder has no bony connection to the back
• Shoulder has muscular connection to the back
  
  • Levator scapulae
  • Rhomboids
  • Latissimus dorsi
  • Trapezius
• Sternoclaviicular joint
  
  • Only bony connection to axial skeleton
• Shoulder joint = glenohumeral joint

Question 2

Axilla

Answer 2

• “Portal into the upper limb” from neck
• Pass through axilla:
  
  • Arterial supply
  • Venous drainage
  • Lymphatic drainage
    
    • From upper limb, anterior chest wall (breast), back, neck
  • Nerve supply
  • Muscle
    
    • Short head of biceps brachii
    • Coracobrachialis
• Apex, base, 3 walls:
  
  • Anterior wall
    
    • Pectoralis major (Attaches to lateral lip of the groove)
    • Pectoralis minor
  • Posterior wall
    
    • Subscapularis (Attaches to the posterior lip of the groove
    • Latissmus dorsi (Attaches to the floor of the groove)
    • Teres major
  • Medial wall
    
    • Serratus Anterior
  • Lateral “wall”
    
    • Bicipital groove of the humerus (where anterior and posterior converge)
  • Groove
    
    • Tendon of the long head of the biceps
  • Upper apex
    
    • Aperture between the clavicle and the first rib
  • Floor
    
    • Skin and fascia

Question 3

Axillary Vasculature

Answer 3

• Axillary artery
  
  • Subclavian artery > 1st rib > axillary artery > inferior border of the teres major muscle > brachial artery
  • Divided into 3 parts by pectorialis minor (anteriorly)* refer to atlas (collateral circulation around the shoulder)
    
    • 1st = proximal to the pectoralis minor
      
      • Superior thoracic artery
    • 2nd = behind the pectoralis minor
      
      • Thoracoacromial artery
      • Lateral thoracic artery
    • 3rd = distal to the pectoralis minor
      
      • Subscapular artery
      • Anterior humeral circumflex artery
      • Posterior humeral circumflex artery
• Axillary sheath
  
  • Connective tissue that surrounds axillary artery and brachial plexus
  • Nerves may be compressed by aneurysms of the artery
• Axillary vein
  
  • Subclavian vein > 1st rib > axillary vein (+cephalic vein?) > inferior border of the teres major > basilic vein + brachial veins
  • NOT in axillary sheath
  • Anterior to axillary sheath

Question 4

Brachial Plexus

Answer 4

• Brachial plexus
  
  • Nerve plexus is a network of nerve fibers that arise from multiple sources
  • Nerve supply to upper limbs > sensory and motor innervation
  • Neck > axilla = sorted anterior and posterior > cords
  • Brachial plexus arises from anterior rami of C5 C6 C7 C8 T1
    
    • Individual nerves contain fibers from multiple spinal cord levels
      
      • Ie radial nerve has fibers from C5 C6 C7 C8
  • Collateral nerves (proximal muscles of shoulder and axillary walls)
    
    • Posterior cord > 3 subscapular nerves = muscles of posterior wall of axilla
    • Lateral and medial cords > lateral and medial pectoral nerves > muscles of anterior wall of the axilla
    • Long thoracic nerve > muscle of the medial wall of the axilla
    • Dorsal scapular nerve > shoulder girdle
    • Suprascapular nerves > shoulder girdle
  • Nerves:
    
    • Musculocutaneous nerve (anterior)
      
      • All muscles of the anterior arm
    • Median nerve (anterior)
      
      • Muscles of the anterior forearm (except 1.5 by ulnar nerve)
    • Ulnar nerve (anterior)
      
      • Muscles of anterior hand (rest by median nerve)
    • Radial nerve (posterior)
      
      • All muscles of the posterior arm and forearm
      • There are NO posterior hand muscles
    • Axillary nerve (posterior)
      
      • Deltoid muscle
      • Teres minor

Question 5

Axillary Lymph Nodes

Answer 5

• Axillary lymph nodes
  
  • Clinically important > drains breast (and also upper limb, chest wall, neck, back)
  • Axillary lymph node > subclavian lymph trunk > L to thoracic duct, R to right lymphatic duct
  • 5 groups of axillary lymph nodes
    
    • Anterior nodes (drain anterior chest wall and breast)
    • Posterior nodes (drain posterior chest wall)
    • Lateral nodes (drain upper limb)
    • Central/Apical nodes – collect drainage from anterior, posterior, lateral
    • Efferent drainage > subclavian trunk
  • Lymphadenectomy in the setting of cancer:
    
    • Axillary lymph node dissection (ALND)
      
      • Remove all nodal tissues in the space defined by:
        
        • Axillary vein superiorly
        • Latissimus dorsi inferolaterally
        • Medial border of the pectoralis minor muscle medially
        • Subscapularis muscle posteriorly
    • Sentinel lymph node biopsy (SLNB)
      
      • For primary breast cancer
      • Lymphatic mapping > colored dye + radioactive dye injected into tumor region > the lymph nodes where the dye drains are removed > only removed relevant lymph nodes

Question 6

Segmental Innervation

Answer 6

• Upper limb muscles > “proximo-distal gradient”
  
  • Higher spinal cord = more proximal muscles
    
    • Shoulder innervated by C5 C6
  • Lower spinal cord = more distal muscles
    
    • Hand innervated by C8 and T1
• All muscles innervated by 2 consecutive segments
• Not every segment represented in a terminal nerve innervates every muscle innervataed by that terminal nerve

Question 7

Cutaneous Innvervation

Answer 7

• Hand is MOST important
• Palmar surface
  
  • Median and ulnar nerves
• Dorsum
  
  • Radial and ulnar (small median)

Question 8

Dermatomal Innervation of the Limb

Answer 8

• Segmental distribution of cutaneous sensory information
• Higher spinal cord segments > sensory innervation to the lateral side of the upper limb
• Lower spinal cord segments > sensory innervation to the medial side of the upper limb

Question 9

Nerve Injuries

Answer 9

• Pre-plexus nerve injuries
  
  • Supra-clavicular portion of plexus
  • Ie Injury to the spinal cord, spinal nerve, anterior rami or trunks
    
    • Dermatomal sensory loss
    • Segmental (myotomal) muscular weakness/paresis (no paralysis)
• Post-plexus nerve injuries
  
  • Infra-clavicular portion of plexus
  • Ie Injury to terminal nerves or collateral nerves
    
    • Cutaneous nerve sensory loss
    • Muscle loss (paralysis) related to specific peripheral nerves

Question 10

Vulnerable to Nerves in Axillary Lymph Node Dissection

Answer 10

• Axillary lymph node dissection (ALND)
  
  • Possible injury to 3 nerves
    
    • C5 C6 C7 > long thoracic nerve > serratus anterior muscle
      
      • Medial wall of axilla
      • Injury will paralyze serratus anterior muscle > nothing to hold scapular against poster chest wall > no upward rotation > “winged scapula”
    • Posterior cord > thoracodorsal nerve > latissimus dorsi
      
      • Passes through axiila
      • Latissmus dorsi = extend, adduct, medially rotate
    • Second intercostal nerve > Intercostobrachial nerve > cutaneous sensory innervation of the medial arm
      
      • Injury > chornic post-operative pain/numbness in the medial arm