sternum (anatomy)

Last reviewed 01/2018

• sternum
  • an elongated, flattened bone, forming the middle portion of the anterior wall of the thorax. Its upper end supports the clavicles, and its margins articulate with the cartilages of the first seven pairs of ribs. It consists of three parts, named from above downward, the manubrium, the body or gladiolus, and the xiphoid process (xiphisternum)
• manubrium
  • somewhat quadrangular form, broad and thick above, narrow below at its junction with the body
    • anterior surface
      • convex from side to side, concave from above downward, is smooth, and affords attachment on either side to the sternal origins of the Pectoralis major and Sternocleidomastoideus
    • posterior surface
      • concave and smooth, affords attachment on either side to the Sternohyoideus and Sternothyreoideus
    • superior border
      • thickest and presents at its center the jugular or presternal notch; on either side of the notch is an oval articular surface, directed upward, backward, and lateralward, for articulation with the sternal end of the clavicle
    • inferior border
      • oval and rough, is covered in a fresh state with a thin layer of cartilage, for articulation with the body
    • lateral borders
      • marked above by a depression for the first costal cartilage, and below by a small facet, which, with a similar facet on the upper angle of the body, forms a notch for the reception of the costal cartilage of the second rib
• body (corpus sterni; gladiolus)
  • considerably longer, narrower, and thinner than the manubrium, attains its greatest breadth close to the lower end
    • anterior surface
      • nearly flat, directed upward and forward, and marked by three transverse ridges which cross the bone opposite the third, fourth, and fifth articular depressions
      • attachment on either side to the sternal origin of the Pectoralis major
    • posterior surface
      • slightly concave, is also marked by three transverse lines, less distinct, however, than those in front; from its lower part, on either side, the Transversus thoracis takes origin
    • superior border
      • oval and articulates with the manubrium, the junction of the two forming the sternal angle (angulus Ludovici)
    • inferior border
      • narrow, and articulates with the xiphoid process
    • lateral border
      • each, at its superior angle, has a small facet, which with a similar facet on the manubrium, forms a cavity for the cartilage of the second rib; below this are four angular depressions which receive the cartilages of the third, fourth, fifth, and sixth ribs, while the inferior angle has a small facet, which, with a corresponding one on the xiphoid process, forms a notch for the cartilage of the seventh rib
        • articular depressions are separated by a series of curved interarticular intervals, which diminish in length from above downward, and correspond to the intercostal spaces
• xiphoid process (processus xiphoideus; ensiform or xiphoid appendix; xiphisternum)
  • xiphoid process is the smallest of the three pieces: it is thin and elongated, cartilaginous in structure in youth, but more or less ossified at its upper part in the adult
    • anterior surface
      • affords attachment on either side to the anterior costoxiphoid ligament and a small part of the Rectus abdominis
    • posterior surface
      • affords attachment to the posterior costoxiphoid ligament and to some of the fibers of the diaphragm and Transversus thoracis
    • lateral borders
      • affords attachment to the aponeuroses of the abdominal muscles
    • above, it articulates with the lower end of the body, and on the front of each superior angle presents a facet for part of the cartilage of the seventh rib; below, by its pointed extremity, it gives attachment to the linea alba
    • xiphoid process varies much in form; it may be broad and thin, pointed, bifid, perforated, curved, or deflected considerably to one or other side