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1. Thoracic wall

Bones

  • Sternum: manubrium, body, xiphoid process. Sternal angle (angle of Louis) at T4–T5 – landmark for rib 2, tracheal bifurcation.
  • Ribs: 12 pairs. True ribs (1–7) attach directly to sternum via costal cartilages. False ribs (8–10) have indirect attachment (cartilage of rib 7). Floating ribs (11–12) – no anterior attachment.
  • Thoracic vertebrae: T1–T12 articulate with ribs via costovertebral and costotransverse joints.

Joints

  • Costovertebral joints: head of rib articulates with vertebral body (demifacets).
  • Costotransverse joints: tubercle of rib articulates with transverse process (T1–T10).
  • Sternocostal joints: 1st rib synchondrosis; ribs 2–7 synovial.
💡 clinical pearl

Rib fractures most commonly occur at the angle (weakest point); flail chest = multiple adjacent ribs fractured in ≥2 places → paradoxical movement.

2. Muscles of the thorax

Intercostal muscles

  • External intercostals: fibers downward and forward; elevate ribs during inspiration.
  • Internal intercostals: fibers downward and backward; depress ribs (forced expiration).
  • Innermost intercostals: deepest layer, separated by neurovascular bundle.

Accessory muscles

  • Serratus anterior (long thoracic nerve) – winging if injured
  • Pectoralis major & minor
  • Subclavius – protects neurovascular bundle
📐 note:

Innermost intercostals are continuous with the transversus thoracis and subcostal muscles.

3. Neurovascular supply

Intercostal neurovascular bundle

Runs in the costal groove between internal and innermost intercostal muscles. Order (superior to inferior): VAN → Vein, Artery, Nerve.

Clinical thoracentesis: needle inserted above the rib to avoid injuring the bundle.

Arteries

Posterior intercostals (from aorta), anterior intercostals (from internal thoracic).

Nerves

Intercostal nerves T1–T11 (anterior rami), subcostal T12.

4. Thoracic cavities

The thoracic cavity is divided into three major compartments:

  • Right pleural cavity: contains right lung.
  • Left pleural cavity: contains left lung.
  • Mediastinum: central compartment (heart, great vessels, esophagus, trachea, thymus).

5. Mediastinum divisions

Superior mediastinum

Above the sternal angle (T4–T5). Contains: arch of aorta, brachiocephalic veins, SVC, trachea, esophagus, thoracic duct, thymus, vagus & phrenic nerves.

Inferior mediastinum

Subdivided into:

  • Anterior: thymus, fat, lymph nodes
  • Middle: heart and pericardium
  • Posterior: esophagus, descending aorta, thoracic duct, azygos veins

6. Pleura

Parietal pleura: lines thoracic wall, mediastinum, diaphragm. Visceral pleura: covers lung surface. Between them: pleural cavity with serous fluid (reduces friction).

clinical
  • Pleural effusion – fluid in cavity
  • Pneumothorax – air in cavity
  • Hemothorax – blood
innervation

Parietal pleura: intercostal nerves (somatic) → pain. Visceral pleura: autonomic (insensitive to pain).

7. Lungs

Right lung

3 lobes: superior, middle, inferior (horizontal and oblique fissures).

Left lung

2 lobes: superior, inferior (oblique fissure). Has cardiac notch and lingula (homologous to right middle lobe).

Bronchopulmonary segments

10 on right, 8–10 on left. Each is a functional unit supplied by a segmental bronchus and branch of pulmonary artery; surgically resectable.

8. Trachea and bronchi

Trachea bifurcates at carina (T4–T5) into:

  • Right main bronchus: wider, shorter, more vertical → common site for aspiration.
  • Left main bronchus: narrower, longer, more horizontal.

9. Heart and pericardium

Pericardium: fibrous pericardium (tough outer) and serous pericardium (parietal layer lines fibrous, visceral layer = epicardium). Pericardial cavity contains fluid (~20 ml).

Major topics: chambers, coronary circulation (LAD, LCx, RCA), conduction system (SA node, AV node, bundle of His).

⚠️ cardiac tamponade

Fluid in pericardial cavity → compression of heart → pulsus paradoxus, muffled heart sounds, elevated JVP (Beck’s triad).

10. Major thoracic vessels

  • Ascending aorta
  • Aortic arch (brachiocephalic, left common carotid, left subclavian)
  • Thoracic aorta (descending)
  • Superior vena cava
  • Pulmonary trunk
  • Pulmonary veins (four)
  • Azygos venous system

11. Thoracic nerves

  • Phrenic nerve (C3–C5) – motor to diaphragm; sensory to pericardium, mediastinal pleura. Injury → diaphragm paralysis.
  • Vagus nerve (CN X) – parasympathetic, recurrent laryngeal nerves.
  • Intercostal nerves – T1–T11 somatic motor & sensory.
  • Sympathetic trunk – ganglia, splanchnic nerves.

12. Clinical correlations (frequently tested)

Pneumothorax: air in pleural cavity → lung collapse. Tension pneumothorax shifts mediastinum.
Rib fractures: most common ribs 4–9; flail chest.
Thoracic outlet syndrome: compression of neurovascular bundle (C8–T1, subclavian artery) by cervical rib or scalenes.
Pleural effusion: blunting of costophrenic angle; thoracentesis above rib.
Cardiac tamponade: Beck’s triad, pulsus paradoxus.
Lung cancer spread: via lymphatics (hilar, mediastinal, supraclavicular). Pancoast tumor (superior sulcus) involves C8–T1, stellate ganglion → Horner.