Sternum

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Original Editor - Grace Barla

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Description

The sternum (Colored part of figure shown below) is a Sword like flat bone that forms the thoracic skeleton's anterior median section. (BD CHAURASIA:BD_Chaurasia’s_Human_Anatomy, Volume 1 - Upper Limb Thorax, 6th Edition.pdf (archive.org))

Length of the bone: 17 cm {Size of sternum in males is longer than in females}

Figure: Sternum

Structure

The sternum has 3 anatomical parts:

1. Manubrium
2. Body of the sternum
3. Xiphoid process

1) Manubrium:

• Quadrilateral in shape.
• Thickest and Strongest part
• Surfaces:
  • Anterior surface:Convex from side to side; concave from above downwards.
  • Posterior Surface:Concave; it forms the anterior boundary of the superior mediastrernum.

• Borders:
  • Superior border: Thick,rounded and concave
    • marked by the suprasternalnotch or jugular notch or interclavicular notch in the median part
    • The clavicular notch on each side
  • Inferior border: It forms the secondary cartilaginous joint with the body of the sternum.
    • The manubrium makes a slight angle with the body, convex forwards, called the sternal angle of Louis.
  • Two lateral borders: It forms the primary cartilaginous joint with the first costal cartilage.

2) Body of the sternum:

•  The body of the sternum is longer, narrower and thinner than the manubrium
• It is the widest close to its lower end opposite the articulation with the fifth costal cartilage.
•  Surfaces:
  • Anterior surface: It is flat, directed forward and slightly upwards.
  • Posterior surface: slightly concave.
  • 2 lateral borders, upper end and lower end.

3) Xiphoid process:

• The smallest part of the sternum
• It is at first cartilaginous, but later in the adult, it becomes ossified near its upper end.
• It varies in shape: It May be bifid or perforated.
• Surfaces:  
  • Anterior surface
  • Posterior surface
  • Lateral border