Contents

Name of bone

Sternum

Location/Articulation

The sternum is an elongated, flattened bone. Shaped like a capital T, the sternum forms the middle portion of the anterior wall of the thorax, which helps to protect the lungs, heart and major blood vessels from physical trauma. The upper end of the sternum supports the clavicles.

The superior seven costal cartilages articulate with the sternum, forming the costal margin anteriorly. The right and left clavicular notches articulate with the right and left clavicles, respectively. The costal cartilage of the second rib articulates with the sternum at the sternal angle, making it easy to locate.


Figure 1. Thoracic cage, showing location of sternum and ribs

Muscle and ligament attachments

The transversus thoracis muscle is innervated by the intercostal nerve and superiorly attaches at the posterior surface of the lower sternum. Its inferior attachment is the internal surface of costal cartilages two through six and works to depress the ribs.

The upper end of the sternum connects to the sternocleidomastoid muscle.

Surface anatomy

 The sternum consists of three parts, listed superior to inferior:

  • Manubrium, the broad superior portion of the sternum. The suprasternal (jugular) notch is medially located at the superior end of the manubrium. Located superiorly and laterally are the right and left clavicular notches.
  • Body of sternum (gladiolus), the longest part of the sternum. The sternal angle is located at the point where the body joins the manubrium. The sternal angle can be felt at the point where the sternum projects farthest forward. However, in some people the sternal angle is concave or rounded. During physical examinations, the sternal angle is a useful landmark when counting ribs because the second rib attaches here.http://en.wikipedia.org/wiki/Human_sternum#cite_note-KS-0
  • Xiphoid process, located at the inferior end of the sternum. Improperly performed chest compressions during cardiopulmonary resuscitation can cause the xiphoid process to snap off, driving it into the liver, which can cause a fatal hemorrhage.


Figure 1. Posterior surface of the sternum

In its natural position, the inclination of the sternum is oblique from above, downward and forward. The sternum is slightly convex in front and concave behind. It is broad above, becoming narrowed at the point where the manubrium joins the body, after which it again widens a little to below the middle of the body, and then narrows to its lower extremity. The average length of the sternum in an adult is about 17 cm; it is longer in the male than in the female.

In early life, the body of the sternum is divided in three segments, called sternebrœ.

The sternum is composed of highly vascular tissue, covered by a thin layer of compact bone which is thickest in the manubrium between the articular facets for the clavicles.

Radiography

Physical examination

Embryology

Anomalies

A somewhat rare congenital condition of the sternum is a sternal foramen, a single round hole in the sternum that is present from birth and usually is off-centered to the right or left, commonly forming in the 2nd, 3rd, and 4th segments of the sternum body. Sternal foramens can often be mistaken for bullet holes.

Injuries/Disorders

Fractures of the sternum are rather uncommon. They may result from trauma, such as when a driver’s chest is forced into the steering column of a car in a car accident or from repeated punches or continual beatings to the sternum area. Sternum fractures are frequently associated with underlying injuries such as pulmonary contusions.

A fracture of the sternum is usually a comminuted fracture. The most common site of sternal fractures is at the sternal angle.

Attachments:


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