AnatomyThoraxThoracic wallSternum

AnatomyThoraxThoracic wallSternum

Sternum

Author: Shahab Shahid, MBBS • Reviewer: Uruj Zehra, MBBS, MPhil, PhD
Last reviewed: October 26, 2023
Reading time: 8 minutes

The sternum is the bone that lies in the anterior midline of our thorax. It forms part of the rib cage and the anterior-most part of the thorax. Its functions are to protect the thoracic organs from trauma and also form the bony attachment for various muscles. It is also the center around which the superior 10 ribs directly or indirectly attached.

There are certain congenital pathological conditions related to the sternum. They mostly refer to the deviations of the shape of the sternum, which in some cases, especially if it is an extreme deviation, can affect the organs within thoracic cavity.

Key facts about the sternum
Function	Protection of the lungs, heart and thoracic blood vessels from mechanical damage
Embryological development	Develops from a left and right cartilaginous plates that unite in the midline
Parts	Manubrium - most superior region that articulates with clavicles and the first pair of ribs Body - articulates with 3rd - 7th ribs Xiphoid process - most inferior part
Clinical relations	Sternotomy, sternoclavicular joint dislocation, fracture, pectus excavatum, pectus carinatum

In this article, we will discuss the embryology, anatomy and clinical relevance of the sternum.

Contents

Embryology
Anatomy
Clinical points
Sources

+ Show all

Embryology

The sternum develops from a left and right cartilaginous plates that unite in the midline.
The ribs develop from their ossification centers and unite with the sternum in the midline.
The manubrium and xiphoid process usually develop from one ossification centre each, but the sternebral centres are commonly paired either symmetric or asymmetric.
The xiphoid process does not fully join the body of the sternum until adulthood.

Anatomy

The word sternum originates from the ancient Greek word ‘sternon’, meaning chest. The sternum is also known as the breastbone. It is a flat bone that articulates with the clavicle and the costal cartilages of the upper 7 ribs (true ribs), while the 8th, 9th and 10th ribs (false ribs) are indirectly attached with sternum via costal cartilage of the ribs above. The bone is divided into three parts:

The manubrium.
The body of the sternum (mesosternum).
The xiphoid process (xiphisternum).

The sternum lies very superficially in the anterior thorax and is easily palpable below the skin of the chest in the midline. The bone covers and protects the heart and great vessels in part, as well as the trachea and esophagus.

Test what you already know about the sternum with the following quiz:

Manubrium

The manubrium is a large quadrangular shaped bone that lies above the body of the sternum. The lower border is narrower, is quite rough, and articulates with the body with a thin layer of cartilage in between. At the superior border of the bone is the jugular notch or suprasternal notch, fibers of interclavicular ligaments are attached here. The clavicular notches for the articulation of clavicles are projected upward and laterally on both sides of the jugular notch. The costal cartilages of the first rib and part of the second rib also articulate with the manubrium, and they fit into facets on its lateral border.

The sternal fibers of pectoralis major and sternocleidomastoid are attached to the anterior surface. Posterior surface gives attachment to sternohyoid and sternothyroid muscles. The superior sternopericardial ligament connects the pericardium (that lies in the superior part of the middle mediastinum) to the manubrium. The lower border of the manubrium articulates with the body of the sternum at the sternal angle (of Louis), it is where the second pair of costal cartilage attaches to the sternum and at the level of the inferior border of T4, is also clinically known as the Angle of Louis. The second intercostal space can be palpated on either side of this projection and is the location for auscultation of the pulmonary and aortic area on left and right respectively.

Sternum in cadaver: Notice how manubrium articulates with the clavicle via the clavicular notches and with the first rib at its lateral surface.

Body of the sternum

The body of the bone (also known as the gladiolus) is a long flat structure, with a convex anterior surface, and a concave posterior surface. It has facets on each of its lateral borders for articulation with the costal cartilage of the 3rd to 7th ribs along with part of the second costal cartilage.

The sternocostal head of the pectoralis major muscle attaches the sternum, on the lateral sides of its anterior surface. The posterior surface of the body gives rise to the transversus thoracis muscle (innervated by intercostal nerves). The lower part of the bone is narrower and articulates with the xiphoid process.

Xiphoid process

The xiphoid process is a small projection of bone which is usually pointed. It possesses demifacets for part of seventh costal cartilage at its superolateral angle.

The fibres of rectus abdominis and aponeurosis of internal and external obliques are attached to its anterior surface. Posterior surface gives rise to the inferior sternopericardial ligament.

It also is the site of insertion of part of the thoracic diaphragm. Blood supply to the sternum arises from the internal thoracic artery.

Clinical points

Sternotomy/cardiothoracic surgery

Open cardiothoracic surgery requires the sternum to be divided and splayed open to access the thoracic organs. This technique can be used for coronary artery surgery, and open abdominal aortic aneurysm repair. However, as minimally invasive radiologically guided techniques such as EVAR (endovascular aneurysm repair) have developed, sternotomy is being used less and less. The newer approaches lead to a shorter recovery time and less morbidity for the patient.

Sternoclavicular joint dislocation

This is an uncommon dislocation, and due to its close location to the great vessels, is potentially rapidly dangerous. Symptoms will include soreness around the area, and if the great vessels are compromised, sudden death.

Sternal fracture

This is a rare fracture and most commonly results from a motor vehicle accident, or high impact direct trauma of another cause. The manubrium is the most commonly injured part of the bone. Due to their direct connection and proximity, the ribs are also commonly fractured in the process. The vital organs can be compromised.

Bone marrow biopsy

The sternum is used as the site for bone marrow biopsy in obese or overweight patients, where access to the iliac crest is limited.

Pectus excavatum

Pectus excavatum is a condition also known as funnel chest, where the sternum and superior ribs grow abnormally, creating a sunken chest appearance. Causes include Marfan syndrome (fibrillin defect) and Ehler’s Danlos syndrome (collagen defect).

Pectus carinatum

This is the opposite of pectus excavatum, and occurs when the ribs and sternum grow abnormally, so the sternum protrudes outwards. The chest is shaped like a bird’s, this condition is also a feature in many syndromes like Down’s syndrome, Marfan syndrome, and osteogenesis imperfecta.

Sources

All content published on Kenhub is reviewed by medical and anatomy experts. The information we provide is grounded on academic literature and peer-reviewed research. Kenhub does not provide medical advice. You can learn more about our content creation and review standards by reading our content quality guidelines.

References:

Frank H.Netter MD: Atlas of Human Anatomy, 5th Edition, Elsevier Saunders.
Chummy S.Sinnatamby: Last’s Anatomy Regional and Applied, 12th Edition, Churchill Livingstone Elsevier.
Richard L. Drake, A. Wayne Vogl, Adam. W.M. Mitchell: Gray’s Anatomy for Students, 2nd Edition, Churchill Livingstone Elsevier.
Ibrahim D. MD and Knipe H. MD et al: Sternal fracture. Radiopaedia.org (accessed 14/02/2016).
Hacking C. MD: Normal lateral sternum. Radiopaedia.org (accessed 14/02/2016).
Neil K. Kaneshiro MD: Pectus carinatum. MedlinePlus (accessed 14/02/2016).
The Sternum. Henry Gray (1821–1865). Anatomy of the Human Body (accessed 14/02/2016).

Illustrators:

Overview of the sternum (lateral and anterior view) - Begoña Rodriguez
Bones of the thorax (cadaveric dissection) - Prof. Carlos Suárez-Quian

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