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AN10.1-13 | Axilla, Shoulder and Scapular region — Summary & Reflection

REFLECT

Stand up and try these movements with your own shoulder:

  1. Abduct your arm slowly from 0° to 180°. Can you feel the transition from supraspinatus (0–15°) to deltoid (15–90°) to scapular rotation (90–180°)? Place your other hand on your scapula and feel it rotate.
  2. Laterally rotate your arm (turn palm forward, elbow at side). You're using infraspinatus and teres minor.
  3. Shrug your shoulders (trapezius), then squeeze your shoulder blades together (middle trapezius).
  4. Push against a wall and look at your scapula in a mirror — is there any winging? (There shouldn't be, unless your long thoracic nerve is damaged!)

Now consider: a patient falls off a motorcycle and can't abduct their arm past 15°. Which muscle is likely damaged, and which nerve supplies it?

KEY TAKEAWAYS

Key takeaways — your study checklist:

  1. The axilla is a pyramid-shaped space: apex (cervicoaxillary canal), base (skin), anterior wall (pectorals), posterior wall (subscapularis, latissimus, teres major), medial wall (ribs + serratus anterior), lateral wall (humerus).
  2. Axillary artery has 3 parts (divided by pectoralis minor): 1 branch, 2 branches, 3 branches.
  3. Axillary lymph nodes — 5 groups: anterior (pectoral), posterior (subscapular), lateral, central, apical. Critical for breast cancer staging.
  4. Brachial plexus — 5 levels: Roots (C5–T1) → Trunks → Divisions → Cords → Branches. Mnemonic: Robert Taylor Drinks Cold Beer.
  5. Erb's palsy (C5,C6 — upper trunk) = waiter's tip position. Klumpke's paralysis (C8,T1 — lower trunk) = claw hand ± Horner's syndrome.
  6. Rotator cuff = SITS: Supraspinatus (initiates abduction), Infraspinatus (lateral rotation), Teres minor (lateral rotation), Subscapularis (medial rotation). Supraspinatus is the most commonly torn.
  7. Serratus anterior (long thoracic nerve) — damage causes winged scapula.
  8. Shoulder joint — most mobile but least stable. Most common dislocation: anteroinferior.
  9. Scapular anastomosis — backup blood supply connecting subclavian and axillary systems.
  10. Axillary nerve wraps around the surgical neck of the humerus. Safe deltoid injection: upper third, 2–3 finger-breadths below acromion.