sternum

The sternum, or breastbone, is a flat, elongated bone located along the midline of the anterior chest. It forms the front portion of the thoracic cage and, with the ribcarts and clavicles, helps protect the heart, lungs, and great vessels while providing attachment for the muscles of the chest, neck, and upper limbs.

Anatomy and parts: The sternum is traditionally described as having three main parts—the broad superior manubrium, the central body (corpus sterni), and the small inferior xiphoid process. The jugular notch sits at the superior border of the manubrium. The sternal angle, or Angle of Louis, is the junction between the manubrium and the body and typically lies opposite the second rib, around the level of T4–T5.

Articulations and connections: The sternum articulates with the clavicles at the sternoclavicular joints and with the costal cartilages of the true ribs. The first rib attaches to the manubrium, and ribs 2 through 7 attach along the lateral borders of the manubrium and body via costal cartilages. Ribs 8 through 10 connect indirectly through the cartilage of rib 7, while ribs 11 and 12 do not attach to the sternum.

Development and variation: The sternum ossifies from multiple centers and fibrously fuses during adulthood. The xiphoid process shows considerable variation in shape and ossification among individuals.

Clinical relevance: The sternum serves as a landmark for chest procedures and resuscitation. It is the site of median sternotomy to access the heart and great vessels in cardiothoracic surgery, and conditions affecting the sternum or thoracic wall can influence chest mechanics and protection of intrathoracic organs.