Sternum

1. Overview

The sternum, or breastbone, is a flat, elongated bone located in the center of the anterior thoracic wall. It forms the anterior portion of the rib cage and provides protection to vital thoracic organs, including the heart and major blood vessels. The sternum also serves as an essential anchor point for ribs and clavicles.

2. Location

The sternum is situated in the midline of the anterior thorax:

• Anterior to: The heart, great vessels, and upper mediastinum.

• Medial to: The ribs and costal cartilages.

• Superiorly: Articulates with the clavicles and the first pair of ribs.

• Inferiorly: Ends just above the xiphoid process and costal arch.

3. Structure

The sternum is a flat bone composed of three parts:

• Manubrium:

  • Uppermost, triangular portion.

  • Articulates with the clavicles (at the sternoclavicular joints) and first two pairs of ribs.

  • Features include the jugular (suprasternal) notch and clavicular notches.

• Body (gladiolus):

  • Longest central portion of the sternum.

  • Articulates with costal cartilages of ribs 2 to 7.

  • Connected to the manubrium at the sternal angle (Angle of Louis), a key clinical landmark.

• Xiphoid process:

  • Small, cartilaginous projection at birth that ossifies with age.

  • May vary in shape and size; serves as an attachment for muscles like the diaphragm and rectus abdominis.

The sternum has an internal spongy bone structure with a thin layer of compact bone externally and is rich in red bone marrow.

4. Function

The sternum performs several structural and protective roles:

• Protects thoracic organs: Shields the heart, great vessels, and part of the lungs from trauma.

• Attachment point: Provides anchorage for ribs (via costal cartilages) and clavicles, maintaining the structural integrity of the thoracic cage.

• Supports respiration: Moves slightly during breathing, facilitating thoracic expansion and contraction.

• Muscle origin: Serves as an attachment site for the pectoralis major, sternocleidomastoid, sternohyoid, and other muscles.

5. Physiological role(s)

Though primarily structural, the sternum contributes to physiological processes:

• Hematopoiesis: Contains red bone marrow, especially in the manubrium and body, active in producing blood cells.

• Landmark for procedures: Used for sternal puncture or bone marrow biopsy in adults.

• Postural alignment: Acts as a central anchor for rib movements and spinal posture in the thoracic region.

6. Clinical Significance

The sternum plays a role in various clinical and surgical contexts:

• Sternal fractures:

  • Often due to blunt trauma (e.g., motor vehicle collisions); can injure underlying heart or great vessels.

• Sternal angle (Angle of Louis):

  • Important landmark for rib counting and auscultation; marks the level of the 2nd rib and bifurcation of the trachea.

• Sternal puncture:

  • Used to access bone marrow in diagnostics for leukemia, lymphoma, or anemia.

• Mediastinal surgery:

  • The sternum is often divided (median sternotomy) to access the heart and lungs in procedures like open-heart surgery.

• Xiphoid process issues:

  • Can cause xiphodynia—pain or discomfort from inflammation or trauma.

• Congenital anomalies:

  • Includes cleft sternum or pectus carinatum/excavatum, which may require surgical correction for functional or cosmetic reasons.