Kylkiruston

Kylkiruston is the Finnish term for the costal cartilage, the hyaline cartilage segments that connect the ribs to the sternum or to other costal cartilage. Together with the sternum and thoracic vertebrae, these cartilages form the anterior portion of the thoracic cage and contribute to its elasticity and resilience.

Anatomy and connections: Each rib has an anterior costal cartilage that links it to the sternum or to the cartilage above. Ribs 1–7 connect directly to the sternum via their costal cartilages. Ribs 8–10 connect to the cartilage of the rib above, forming the false ribs. Ribs 11 and 12 do not reach the sternum (floating ribs). The costochondral joints, where cartilage meets bone, enable limited movement and help accommodate respiratory expansion.

Development and histology: Costal cartilages arise from mesenchymal tissue during fetal development and remain cartilaginous into adulthood, though calcification can occur with aging. Histologically they are composed of hyaline cartilage, rich in extracellular matrix with type II collagen and chondrocytes within lacunae, surrounded by a perichondrium.

Function: The costal cartilages provide flexibility to the thoracic cage, allowing the chest to expand and contract during breathing while protecting the underlying structures. They also help distribute mechanical loads and contribute to the contour of the chest.

Clinical notes: Disorders affecting kylkiruston include costochondritis (inflammation of costal cartilage at the costochondral junction) and, less commonly, injuries such as costal cartilage fractures or costochondral separations. Calcification or degeneration of the cartilages can occur with age or disease.

See also: rib, sternum, costochondral junction, thoracic cage.