Sternum

The sternum completes the anterior chest wall as the ventral breastplate.

Gross anatomy

The sternum is composed of a manubrium, a body and the inferior xiphisternum or xiphoid process. These articulations are via hyaline cartilage with a fibrocartilaginous intervening disc: 

• the manubrium is flat and four-sided, wider superiorly
• the body is a flat rectangular bone that has grooves (facets) on its lateral border for articulation with the ribs:
  • approximately 20 cm long
  • 3-4 cm wide
  • 1 cm thick
• the xiphoid process is a thin bony projection inferiorly
  

Articulations

• superiorly the manubrium attaches to the neck where the two deep layers of cervical investing fascia insert
• the manubrium articulates with the first rib and clavicle
• the body articulates with the second rib at the angle of Louis as well as the 2^nd to 7^th rib and costal cartilages
• inferiorly articulates with xiphoid cartilaginous joint

Attachments

Musculotendinous

• muscular attachments: sternocleidomastoid, intercostal muscles, pectoralis major, sternohyoid, sternothyroid
• transversus thoracis arises from the posterior surface of the body
• the xiphisternum attaches to linea alba

Ligamentous

• sternopericardial ligaments secure the fibrous pericardium to it
• interclavicular ligament
• anterior and posterior sternoclavicular ligaments (thickenings of the sternoclavicular joint capsule)

Blood supply

• nutrient branches from internal thoracic (mammary) artery and vein
• deep to the sternum is the internal thoracic artery and veins laterally

Nerve supply 

• nerve supply is via intercostal nerves (which arise from the anterior rami of thoracic spinal nerves)

Lymphatics

• chain of internal mammary lymph nodes

Variant anatomy 

• episternal ossicle
• manubriosternal and sternoxiphoidal fusion
• sternal and xiphoid foramen
• sternal cleft and band
• sternal defect (notch)
• tilted sternum: oblique instead of horizontal orientation in the medial-lateral plane ⁵
• suprasternal tubercle
• unfused sternal body segments
• xiphoid shape variations

See also

• pectus carinatum
• pectus excavatum