Axilla - Boundaries, Arteries, and Brachial Plexus

1. Boundaries of Axilla
• Superior boundary - first rib, clavical, upper border of scapula
• Inferior boundary - skin of armpit
• Anterior border - pectoralis major (pectoralis minor)
• Posterior border - teres major, latissimus dorsi, subscapularis
• Medial boundary - thoracic wall (serratus anterior)
• Lateral boundary - intertubercular sulcus (humerus)
2. Cephalic vein - entering the axilla by way of the clavipectoral fascia
3. Axillary sheath - surrounding the brachial plexus and axillary artery (axillary vein?), invagination of the prevertebral fascia
4. Axillary artery - from first rib to inferior border of teres major, divided into 3 parts by anterior relationship of teres minor
5. Six branches of the axillary artery
1. Superior thoracic artery - first and second intercostal spaces
2. Thoracoacromial artery - branches: acromial, deltoid, pectoral, clavicular (acromial and deltoid branches are key players in shoulder anastomosis)
3. Lateral thoracic artery - usually off axillary artery (can arise from subscapular or thoracodorsal arteries, runs along thoracic wall about 1-2 inches anterior to long thoracic nerve
4. Subscapular artery - terminates as the circumflex scapular (scapular anastomosis) and thoracodorsal arteries
5. Posterior humeral circumflex artery - passes through quadrangular space, can arise from subscapular artery, shoulder anastomosis (ascending branch of deep brachial artery)
6. Anterior humeral circumflex artery - passes anterior surface of surgical neck of humerus, shoulder anastomosis, can arise from common trunk with posterior humeral circumflex artery
6. Cords of the brachial plexus (see the "M" (lonely posterior cord is left out))
1. Lateral cord (3) - lateral pectoral n., lateral root median n., musculocutaneous n.
2. Medial cord (3) - medial pectoral n., medial root median n., ulnar n., (medial cutaneous nn of arm and forearm)
3. Posterior cord (5) - upper subscapular n. (subscapularis), middle subscapular (thoracodorsal n., latissimus dorsi), lower subscapular (subscapularis and teres major)
axillary n. (quandrangular space, deltoid, teres minor), radial n. (triangular interval)
7. Long thoracic nerve (nerve to serratus anterior (of Bell)) - vertical descent on thoracic wall about 1.5" posterior to lateral thoracic a.