Sternum

General

Illustration of the sternum and ribs

Illustration of the sternum with muscle attachments labeled

Anterior view of the sternum

Normal sternal anatomy. Coronal reformatted image from chest CT shows the three parts of the sternum—the manubrium (M), sternal body (B), and xiphoid process (X)—as well as the clavicles (C), internal mammary arteries (arrowheads), and anterior (red) and posterior (blue) muscular insertions, including the origins of the sternocleidomastoideus (1), subclavius (2), and pectoralis major (3); attachments of the sternohyoideus (4) and sternothyroideus (5); origin of the transversus thoracis (6); and attachments of the small part of the rectus abdominis (7) and fibers of the diaphragm and transversus thoracis (8).

Description

• The sternum is often referred to as the breastbone
• Other names: breast bone, ventral breastplate
• Flat bone, located on anterior aspect of thorax
• Compact cortex, slightly convex anteriorly
• Multiple indentations/ costal notches along the borders

Manubrium

• Trapezoid shaped superior part of the sternum
• Jugular notch: depression at the top
• Fossa on each side articulates with clavicle, forming sternoclavicular joint
• Facet for articulation with the 1st Rib
• Demifact for articulation with 2nd Rib
• Sternal angle: inferiorly articulates with the body of sternum

Body

• Largest part of sternum, flat and elnogated
• Articualtes with both the manibrum (manubriosternal joint), xiphoid process (xiphisternal joint)
• Articular facets for Ribs 3 through 6
• Demifacts for Rib 2 and 7

Xiphoid Process

• Smallest, most inferior part of sternum
• Tip is located approximately at the level of T10 vertebrae
• Largely cartilaginous, ossifies later in life around age 40
• In some individuals, articulates with 7th Rib

Articulations

• Manubrium
  • First rib (primary cartilaginous)
  • Clavicle (atypical synovial), forming sternoclavicular joint
  • Body of the sternum (secondary or primary cartilaginous joint)
• Body
  • Articulates with the second rib at the sternomanubrial angle
  • 3rd to 7th rib and costal cartilages
  • Xiphisternal joint, a secondary cartilaginous joint (symphysis)

Muscle Attachments

• Sternocleidomastoid
• Intercostal Muscles
• Pectoralis Major
• Sternohyoid
• Sternothyroid
• Transversus Thoracis

Actions

• Protect the internal thoracic viscera
• Assist in respiration
• Attachment for ribs

Vascular Supply

• Arterial
  • Nutrient branches from internal thoracic (mammary) artery
  • Internal thoracic artery
• Venous
  • Tributaries of the internal thoracic veins

Innervation

• Intercostal Nerves

Sternal Foramen

• Developmental variant of the sternum resulting in incomplete fusion of the ossification centers

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Clinical Significance

• Sternoclavicular Joint Dislocation
• Clavicle Fracture
• Sternoclavicular Arthritis
• Costochondritis
• Sternal Fracture

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See Also

• Shoulder Pain Main
• Shoulder Anatomy Main
• Physical Exam Shoulder

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