Skeleton of the Thorax
- Thoracic cage: The sternum, ribs, thoracic vertebrae, and costal cartilages form a protective framework around the heart and lungs. Its movable joints also allow changes in thoracic volume during breathing.
- The costal cartilages are flexible cartilage bars that connect ribs to the sternum or costal margin, allowing the thoracic cage to protect organs while still expanding during inspiration.
- Sternum: The sternum has a manubrium, body, and xiphoid process. The manubrium is broadest superiorly, while the body forms most of the anterior thoracic wall.
- Jugular notch: This midline depression marks the superior border of the manubrium. The clavicular notches on either side articulate with the clavicles.
- The manubrium is the superior handle-like part of the sternum, the jugular notch is its midline top depression, the clavicular notches receive the clavicles, and the xiphoid process is the small inferior tip.
- Sternal angle: The manubriosternal junction identifies the second costal cartilage and the transverse thoracic plane. This plane also corresponds approximately to the end of the aortic arch, tracheal bifurcation, and boundary between superior and inferior mediastinum.
- The transverse thoracic plane is an imaginary horizontal level through the sternal angle and T4-T5 region that helps locate major structures inside the chest.
- Sternal body: The body articulates directly with costal cartilages 2 through 7. Cartilages 8 through 10 join the cartilage above to create the costal margin rather than attaching directly to the sternum.
- Xiphoid process: This inferior sternal component varies in shape and may ossify with age. Its position is clinically important because deep pressure or needle placement near it can injure underlying structures.
- Typical rib: A typical rib has a head, neck, tubercle, angle, shaft, and costal groove. These features reflect its vertebral articulation, muscle attachments, and neurovascular relationships.
- From posterior to anterior, a typical rib uses its head and tubercle for vertebral joints, its angle as a bend point, its shaft as the long curved body, and its costal groove to protect intercostal vessels and nerve.
- Rib head: The head articulates with vertebral bodies, usually contacting the body of its corresponding vertebra and the one above through a crest and articular facets.
- Rib tubercle: The tubercle articulates with the transverse process of the corresponding vertebra. Its nonarticular portion also provides an attachment site for ligaments.
- Costal groove: The groove along the inferior internal border shelters the intercostal vein, artery, and nerve. Their usual superior-to-inferior order is VAN, so procedures are placed close to the superior border of the rib below.
- True ribs: Ribs 1 through 7 attach directly to the sternum through their own costal cartilages. Their anterior attachment gives the upper thoracic cage greater structural stability.
- False ribs: Ribs 8 through 10 attach indirectly by joining the costal cartilage above. These articulations contribute to the flexible costal margin.
- Floating ribs: Ribs 11 and 12 have no anterior attachment. Their free anterior ends are embedded in posterior abdominal wall musculature.
- The costal margin is the lower anterior edge of the rib cage, formed mainly by the joined cartilages of false ribs rather than by direct rib-to-sternum attachments.
- First rib: Rib 1 is short, broad, and strongly curved. It has one facet for T1 and grooves for the subclavian vein and artery separated by the scalene tubercle.
- The scalene tubercle is a small bump for anterior scalene attachment; the subclavian vein groove lies anterior to it and the subclavian artery groove lies posterior to it.
- Second rib: Rib 2 bears a tuberosity for serratus anterior. It is less curved than rib 1 and serves as a transition toward the typical ribs.
- Eleventh and twelfth ribs: These ribs lack necks and tubercles because they do not form costotransverse joints. Their simplified posterior ends increase mobility of the inferior thoracic cage.
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