Body of sternum

At a glance

English

Body of sternum

Latin (TA2)

Corpus sterni

System

Bone

Region

Thorax

Side

Single, on the midline

Muscles on it

Sternocostal head of pectoralis major

About the body of sternum

The body of the sternum is its longest part, a flat strip of bone that runs down the front of the chest from the manubrium to the xiphoid process. It is narrow above, broadest a little below its middle, and thinner than the manubrium. It is described as having only a front and a back surface and two side borders. Like the rest of the sternum it is mostly spongy, red-marrow bone with a thin shell of compact bone, which makes it a convenient site for sampling bone marrow.

It forms from four segments, the sternebrae, which fuse in childhood and early adult life. Their joins show as three faint transverse ridges across the front surface, level with the notches for the third, fourth and fifth cartilages, and as less distinct lines behind. A hole, the sternal foramen, is sometimes left in the lower part where the halves of the bone failed to join; it matters because a needle passed there can enter the pericardium.

Each side border carries a row of notches for the costal cartilages. At the top corner a half-facet combines with one on the manubrium to take the second cartilage; below that come notches for cartilages three to six, and at the bottom corner a half-facet shared with the xiphoid takes the seventh. Between the notches the border is curved, and these gaps, shortening from above downwards, face the intercostal spaces. The upper border joins the manubrium, forming the sternal angle, and the narrow lower border meets the xiphoid.

Pectoralis major arises from the front on each side, and transversus thoracis from the lower back surface. Behind the body lie the pericardium and heart, with the edges of the lungs and pleura overlapping it from the sides, so the body is the surface over which chest compressions are pressed. It is divided down the midline in a median sternotomy for heart surgery and then wired together again.

Function and supply

Function

Closes the rib cage in front, anchoring the upper true ribs and shielding the heart, and moves forwards and upwards with them during breathing.

Nerve supply

Not innervated as a muscle is; its periosteum and the overlying skin are supplied by anterior cutaneous branches of the second to sixth intercostal nerves.

Blood supply

Sternal and perforating branches of the internal thoracic arteries on each side.