Costal cartilages

Costal cartilages are bars of hyaline cartilage that connect the anterior ends of the ribs to the sternum, contributing to the elasticity and flexibility of the thoracic wall. Ribs 1–7 are termed "true ribs" because their costal cartilages articulate directly with the sternum. Ribs 8–10, the "false ribs," have costal cartilages that join the cartilage of the rib above, forming the costal margin, while ribs 11 and 12 ("floating ribs") have rudimentary cartilaginous tips that do not attach to the sternum or costal margin.

The costal cartilage is composed of hyaline cartilage surrounded by a fibrous perichondrium, which significantly contributes to its mechanical strength and stiffness.The cartilage is more flexible than bone, allowing for movement during respiration, and its length and proportion relative to the rib vary by rib level and age.

The costal margin, formed by the cartilages of ribs 7–10, is anatomically variable, with frequent interchondral joints and occasional free or hooked tips, especially in the lower ribs.