What is the thoracic cage and what is its function?

The thoracic cage is the osteocartilaginous, elastic framework that forms the thorax. Its main functions are to protect thoracic organs (like the heart and lungs), support respiration by allowing the chest cavity to expand and contract, and serve as an attachment site for muscles of the thorax, upper limbs, back, and diaphragm.

What bones make up the thoracic cage?

The thoracic cage is formed by three main bony components: anteriorly by the sternum (manubrium, body, and xiphoid process), posteriorly by the 12 thoracic vertebrae with intervertebral discs, and laterally by 12 pairs of ribs with their associated costal cartilages.

What are true ribs, false ribs, and floating ribs?

True ribs (1st–7th) articulate directly with the sternum via their costal cartilages. False ribs (8th–10th) articulate indirectly with the sternum by connecting to the cartilage of the rib above. Floating ribs (11th–12th) do not articulate with the sternum or other ribs anteriorly.

How does the shape of the thoracic cage differ between adults and infants?

In cross-section, the adult thorax is kidney-shaped due to obliquely placed ribs, with a greater transverse than anteroposterior diameter. The infant thorax is circular because ribs are more horizontal, making transverse and anteroposterior diameters nearly equal. This affects breathing patterns, with infants relying more on abdominal breathing.

What is the thoracic inlet and what are its boundaries?

The thoracic inlet is the upper opening of the thoracic cavity. Its boundaries are: anteriorly by the upper border of the manubrium sterni, posteriorly by the anterior surface of the T1 vertebra, and laterally by the medial borders of the first ribs and first costal cartilages.

Why is the thoracic cage important for breathing?

The thoracic cage's elastic framework allows the thoracic cavity to expand and contract during respiration. This movement is crucial for lung inflation and deflation. Its shape and rib articulations facilitate this mechanical process, with adults using thoracic expansion more than infants.

What is a clinical implication of the infant thoracic cage shape?

In children under 2 years, the circular thorax limits expansion during breathing, making respiration predominantly abdominal. After abdominal surgeries, pain may cause them to resist abdominal movement, leading to hypoventilation, mucus retention, and increased risk of pneumonia.

Thoracic Cage – Ribs, Sternum & Vertebrae

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