CorpusHuman Anatomy
SkeletalBone group

Thoracic cage

Compages thoracis

Also known as: rib cage, bony thorax

The osteocartilaginous cage formed by the 12 thoracic vertebrae, 12 pairs of ribs with their costal cartilages, and the sternum. It protects the thoracic and upper abdominal organs and is the moving framework of breathing.

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Overview

The cage is narrow above and broad below, kidney-shaped in cross-section. The superior thoracic aperture (thoracic inlet) is bounded by T1, the first ribs and their cartilages, and the upper border of the manubrium; it slopes anteroinferiorly and transmits the trachea, oesophagus, great vessels, nerves and the apices of the lungs. The much larger inferior thoracic aperture (outlet) is bounded by T12, the 11th and 12th ribs, the costal margins (fused cartilages 7–10) and the xiphisternal joint; it is closed by the diaphragm, and the angle between the costal margins is the infrasternal (subcostal) angle.

The cage is protective yet mobile: during inspiration the upper ribs move up and forward, raising the sternum and increasing the anteroposterior diameter (pump-handle movement), while the lower ribs swing upward and outward, increasing the transverse diameter (bucket-handle movement); the diaphragm increases the vertical diameter. Its lower part also protects the liver, spleen, stomach and upper poles of the kidneys.

Location

Chest, from the root of the neck to the upper abdomen.

Parts & subdivisions

  1. Ribs (12 pairs)
    True (1–7), false (8–10), floating (11–12).
  2. Costal cartilages
    Hyaline cartilage extensions of the ribs.
  3. Sternum
    Anterior midline bone.
  4. Thoracic vertebrae
    Posterior pillar.
  5. Superior thoracic aperture
    T1, first ribs, manubrium; site of thoracic outlet syndrome.
  6. Inferior thoracic aperture
    Closed by the diaphragm.

Anatomy

Articulations

Costovertebral (heads of ribs and costotransverse), sternocostal, costochondral, interchondral, manubriosternal and xiphisternal joints.

Function

  • Protects the heart, lungs, great vessels and upper abdominal organs
  • Provides the moving framework for ventilation
  • Attachment for muscles of the neck, upper limb, back, abdomen and the diaphragm
  • Supports the pectoral girdle and upper limbs

Clinical significance

Flail chest

Fracture of ≥3 adjacent ribs each in ≥2 places creates a free segment that moves paradoxically (in on inspiration), with underlying pulmonary contusion and respiratory failure.

Thoracic outlet syndrome

Compression of the lower trunk of the brachial plexus (C8–T1) and/or subclavian vessels at the inlet by a cervical rib, fibrous band or scalene muscles — ulnar-sided paraesthesia and wasting of hand intrinsics, or vascular symptoms.

Pectus excavatum and carinatum

Sunken ("funnel") or protruding ("pigeon") chest due to costal cartilage overgrowth; pectus excavatum is associated with Marfan syndrome.

Compiled from standard anatomy and physiology references — see the Skeletal System sources. For education only; not medical advice.