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Structure

Thoracic cage

Not medically reviewed · Content last updated · 2 min read ·

This is the date the draft was written, not a medical review date.

The thoracic cage is the osteocartilaginous framework of the chest, formed by the thoracic vertebrae, ribs, costal cartilages and sternum. It protects the heart, lungs and great vessels and provides the mechanical basis for breathing.

Terminologia Anatomica (Latin): Cavea thoracis · Open in the 3D atlas

Location

Encloses the thoracic cavity between the superior thoracic aperture (thoracic inlet, bounded by T1, the first ribs and the manubrium) and the wide inferior thoracic aperture closed by the diaphragm.

Structure

Twelve pairs of ribs: ribs 1-7 true (attach directly to the sternum), 8-10 false (attach via the costal cartilage above), 11-12 floating. The sternum has a manubrium, body and xiphoid process; the manubriosternal joint forms the sternal angle (of Louis) at the level of the second costal cartilage and T4-T5 vertebral level. Typical ribs have a head, neck, tubercle and angle; the costal groove carries the intercostal neurovascular bundle.

Blood supply

At group level: posterior intercostal arteries (from the thoracic aorta) and anterior intercostal arteries (from the internal thoracic artery and its musculophrenic branch) anastomose in each space and supply ribs and intercostal muscles; veins drain to the azygos system and internal thoracic veins.

Innervation

At group level the ribs and their periosteum, together with the intercostal muscles and parietal pleura, are supplied by the intercostal nerves (ventral rami of T1-T11) and the subcostal nerve (T12); the diaphragm itself is supplied by the phrenic nerve (C3-C5).

Function

It protects thoracic and upper abdominal organs, supports the shoulder girdle and upper limbs, and changes thoracic volume during breathing: the pump-handle movement increases the anteroposterior diameter and the bucket-handle movement the transverse diameter.

Clinical correlations

Rib fractures are common; ribs 4-9 are most often fractured, and fractures of the lower ribs may injure the spleen or liver, while first-rib fractures imply high-energy trauma. Flail chest (three or more adjacent ribs each fractured in two places) causes paradoxical movement and respiratory compromise. Intercostal drains are inserted just above the rib to avoid the neurovascular bundle. Sternal landmarks (sternal angle) guide cardiac and lung examination; a cervical rib may cause thoracic outlet syndrome.

Common exam points

  • 12 pairs of ribs: 1-7 true, 8-10 false, 11-12 floating.
  • Sternum: manubrium, body, xiphoid; sternal angle at T4-T5 and the second costal cartilage.
  • Intercostal neurovascular bundle runs in the costal groove in the order vein, artery, nerve (VAN) from above downward.
  • Insert chest drains or needles just above the lower rib of the space.
  • Flail chest: segment of chest wall with paradoxical movement; ribs 4-9 most often fractured.

References

  1. Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students. Elsevier — Tier 3 (textbook)
  2. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. Wolters Kluwer, 8th edition (2018) — Tier 3 (textbook)
  3. Netter FH. Atlas of Human Anatomy. Elsevier — Tier 3 (textbook)

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