Thoracic Wall and Diaphragm

Bony Thorax & Joints - Rib Cage Rocks

• Components: Sternum, 12 pairs of ribs, 12 thoracic vertebrae.
• Sternum: Manubrium, Body, Xiphoid process.
  • Sternal angle (Angle of Louis): at T4-T5 IVD level, articulates with 2nd costal cartilage.
• Ribs:
  • True ribs (1-7): Attach directly to sternum.
  • False ribs (8-10): Attach to costal cartilage of rib above.
  • Floating ribs (11-12): No anterior attachment.
  • Typical ribs (3-9): Head, neck, tubercle, shaft.
  • Atypical ribs: 1, 2, 10, 11, 12.
    • Rib 1: Scalene tubercle, grooves for subclavian vessels.
    • Rib 2: Tuberosity for serratus anterior.
• Joints:
  • Costovertebral: Head of rib with vertebral bodies.
  • Costotransverse: Tubercle of rib with transverse process.
  • Sternocostal: Ribs with sternum.
  • Manubriosternal: Symphysis (fibrocartilage).
  • Xiphisternal: Synchondrosis (hyaline cartilage), fuses later.

⭐ Flail chest involves fractures of ≥3 consecutive ribs in ≥2 places, leading to paradoxical respiratory movement.

📌 Superior Thoracic Aperture: Transverse Diameter 10 cm, Anteroposterior Diameter 5 cm (Remember STAD 10-5).

Thoracic Wall Muscles & Fascia - Muscle Power House

• Intercostal Muscles (Primary Respiratory):
  • External: Elevate ribs (inspiration). Fibers: inferoanteriorly (hands in front pockets 📌).
  • Internal: Depress ribs (expiration, except interchondral part). Fibers: inferoposteriorly (hands in back pockets 📌).
  • Innermost: Similar to internal; separated by neurovascular bundle.
• Other Thoracic Wall Muscles:
  • Subcostalis: Posterior; weak expiration.
  • Transversus Thoracis (Sternocostalis): Anterior, depresses cartilages; weak expiration.
  • Levatores Costarum: Elevate ribs; inspiration.
• Key Fascia:
  • Endothoracic Fascia: Lines internal thoracic wall; extrapleural layer.

⭐ The intercostal neurovascular bundle (Vein, Artery, Nerve - VAN, superior to inferior) is located in the costal groove, between internal and innermost intercostal muscles.

Neurovasculature of Thoracic Wall - Wire & Pipe Central

• Nerves: Intercostal (T1-T11 ant. rami), Subcostal (T12).
  • Supply muscles, pleura, skin.
  • Typical (3rd-6th): Thoracic wall only.
  • Atypical (1st, 2nd, 7th-11th): e.g., 1st to brachial plexus, 2nd intercostobrachial n., 7th-11th thoracoabdominal nn.
• Arteries:
  • Posterior Intercostal Arteries (PICA):
    • 1st-2nd spaces: From supreme intercostal a. (costocervical trunk).
    • 3rd-11th spaces & Subcostal a.: From thoracic aorta.
  • Anterior Intercostal Arteries (AICA):
    • 1st-6th spaces: From internal thoracic a.
    • 7th-9th spaces: From musculophrenic a.
  • PICA & AICA anastomose significantly.
• Veins: Generally accompany arteries.
  • Posterior Intercostal Veins: Drain to azygos/hemiazygos venous system.
  • Anterior Intercostal Veins: Drain to internal thoracic/musculophrenic vv.
• Neurovascular Bundle: Runs in costal groove (inferior to rib), between internal & innermost intercostal muscles. Order: Vein, Artery, Nerve (Superior → Inferior) (📌 VAN).

  ⭐ The internal thoracic artery (ITA), particularly the Left ITA (LIMA), is the gold standard conduit for Coronary Artery Bypass Grafting (CABG) due to its excellent long-term patency rates.

Diaphragm - Breathing Boss

• Chief muscle of inspiration; dome-shaped, separates thorax & abdomen.
• Parts & Origin:
  • Sternal: Xiphoid process.
  • Costal: Inner surface of lower 6 costal cartilages & ribs.
  • Vertebral: L1-L3 vertebrae (via crura).
• Insertion: Central tendon.
• Innervation: Phrenic nerve (motor: C3, C4, C5; sensory: phrenic & lower intercostal nerves). 📌 "C3, 4, 5 keeps the diaphragm alive".
• Major Openings (Mnemonic: "I Ate Ten Eggs At Twelve"):
  • Vena Caval (T8): IVC, R. phrenic nerve branches.
  • Esophageal (T10): Esophagus, vagal trunks, esophageal branches of L. gastric vessels.
  • Aortic (T12): Aorta, thoracic duct, azygos vein.
• Action: Inspiration (contraction flattens dome, ↑ thoracic volume). Also involved in straining.

⭐ Unilateral phrenic nerve palsy causes paradoxical upward movement of the affected hemidiaphragm during inspiration.

High-Yield Points - ⚡ Biggest Takeaways

• Typical ribs (3-9) vs. atypical ribs (1, 2, 10-12) have distinct features.
• Intercostal neurovascular bundle (VAN) lies in the costal groove (Vein-Artery-Nerve superior to inferior).
• Diaphragm: Main inspiratory muscle, innervated by phrenic nerve (C3, C4, C5).
• Diaphragmatic apertures: Vena Caval (T8), Esophageal (T10), Aortic (T12).
• Sternal Angle (Angle of Louis): Key landmark at T4/T5, for 2nd rib and tracheal bifurcation.
• Internal thoracic artery gives anterior intercostals, ends as superior epigastric & musculophrenic_arteries_