Sternum

Changed by Grace Carpenter, 17 Nov 2020

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The sternum (plural: sterna or sternums) completes the anterior chest wall as the ventral breastplate.

Gross anatomy

The sternum is composed of a manubrium, a body and the inferior xiphisternum (a.k.a. xiphoid process). They articulate via secondary cartilaginous joints 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 (primary cartilaginous) ~~and~~, clavicle (atypical synovial), and body of the sternum (secondary or primary cartilaginous joint) ⁶
the body articulates with the second rib at the sternomanubrial angle (of Louis , which is in the transthoracic plane of Ludwig) as well as the 3^rd to 7^th rib and costal cartilages
- the articulations of 2^nd and 7^th ribs are shared as demifacets between each of the manubrium and the body, and the body and the xiphoid respectively
inferiorly articulates with ~~xiphoid~~xiphisternal joint, a secondary cartilaginous joint⁶ (symphysis)

Attachments

Musculotendinous

muscular attachments: sternocleidomastoid, intercostal, pectoralis major, sternohyoid, and sternothyroid muscles
transversus thoracis muscle 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)

Arterial supply

nutrient branches from internal thoracic (mammary) artery
deep to the sternum is the internal thoracic artery laterally

Venous drainage

tributaries of the internal thoracic veins, posterolateral to the sternum

Innervation

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

Lymphatic drainage

chain of internal mammary lymph nodes

Variant anatomy

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

~~-<li>the manubrium articulates with the first rib (primary cartilaginous) and clavicle (atypical synovial)</li>~~
+<li>the manubrium articulates with the first rib (primary cartilaginous), clavicle (atypical synovial), and body of the sternum (secondary or primary cartilaginous joint) 6
+</li>
~~-<li>inferiorly articulates with xiphoid cartilaginous joint</li>~~
+<li>inferiorly articulates with xiphisternal joint, a secondary cartilaginous joint 6 (symphysis)</li>

References changed:

6. Susan Standring. Gray's Anatomy E-Book. (2015) <a href="https://books.google.co.uk/books?vid=ISBN9780702068515">ISBN: 9780702068515</a>

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