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StatPearls . Sweetheart Island (FL): StatPearls Publishing; 2021 Jan-.


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Anatomy, Thorax, Sternum

Abdulraheem A. Altalib; catalent H. Miao; Ritesh G. Menezes.

Author Information

Introduction

The sternum is a partially T-shaped upright bone that forms the anterior portion of the chest wall surface centrally. The sternum is divided anatomically into three segments: manubrium, body, and also xiphoid process. The sternum associate the ribs via the costal cartilages forming the anterior rib cage. The manubrium is the broad exceptional segment, the body is the middle portion, and also the xiphoid process is a narrow distal segment forming the partial T-shape. The anatomical position and variations do the sternum critical bony structure of surgical significance. In addition to the anatomy of the sternum, clinical and also forensic ramifications of the sternum are additionally topics in this article.


Structure and Function


The manubrium (manubrium sterni) is quadrangular shame with four borders. The suprasternal notch (jugular notch) is in ~ the premium segment that the manubrium sterni. On either side, the left and right clavicular notches are present. The clavicular notches that the sternum articulate with the medial end of every clavicle to kind the sternoclavicular joints. The manubrium sterni also articulates v the costal cartilages that the first pair the ribs. 
The xiphoid procedure (xiphisternum/xiphoid) is triangular shaped and forms the distal-most part of the sternum. The size and shape that the xiphoid process are highly variable. The is greatly cartilaginous until the age of 40 and becomes completely calcified through the age of 60. However, this age-related alters in the adult xiphoid procedure are also highly variable.
The sternal edge is the projection developed by the junction in between the manubrium sterni and the body of the sternum. This two parts of the sternum lie in slightly various planes resulting in the angulation. This angle coincides anteriorly come the intervertebral disc in between the 4th and fifth thoracic vertebrae. This edge is additionally known together the edge of Louis.
The sternum"s primary duty is to defend the basic mediastinum and its contents native injury. 

Embryology

During the 6th developmental main of fetal life, the sternum establishes independently indigenous a pair the sternal bands dubbed “sternal bars” which room concentrations of mesenchymal cells on either next of the midline.<3> by the 10th week of intrauterine life, these 2 sternal bands arise from the parietal class of the lateral bowl mesoderm bilaterally, then convert into pre-cartilaginous frameworks that migrate and fuse in a craniocaudal direction to form the sternal plate. In the 7th week of intrauterine life, the mesenchyme condenses resulting in the formation of the major cartilaginous design of the 3 sternal segment (manubrium sterni, the human body of the sternum and also the xiphoid process). The cartilaginous sternal model is composed of 6 horizontal departments known together sternebrae. The superior-most sternebra and also the inferior-most sternebra at some point represent the manubrium sterni and also xiphoid process, respectively. The 4 sternebrae the lie in between represent the human body of the sternum.<3> The an initial part of the sternum to kind during embryogenesis is the manubrium sterni followed by the sternal body and also the xiphoid process.   


Blood Supply and Lymphatics

The blood supply of the sternum is mainly derived from the medial horizontal branches that the right and also left inner thoracic arteries i beg your pardon originate directly from the first part that the subclavian arteries bilaterally or periodically originate native a common trunk. The inner thoracic artery offers off sternal, anterior intercostal, perforating and also non-collateral branches. Sternal branches of the interior thoracic arteries which space the main branches providing the sternum space primarily located in the intercostal spaces. Not only sternal branches but additionally perforating branches appear to add to the sternal blood supply.<4><5>

The blood it is provided of the sternum has a significant role in the process of healing following sternotomy procedures.<4> the is likewise important to recognize the blood it is provided of the sternum as sternal epidemic are not uncommon following the harvest of the interior thoracic artery because that coronary artery bypass grafting.<5>

For the venous drainage, the interior thoracic veins drainpipe into the brachiocephalic vein on every side.


Muscles

There are several muscles (muscles of the neck, muscles of the thorax, muscles of the anterior abdominal wall) attached come the sternum.<1> The sternocleidomastoid, sternohyoid and also sternothyroid attach to the manubrium sterni. The transversus thoracis muscle attaches come the body of the sternum and also xiphoid process. Pectoralis major is another significant muscle attached to the body of the sternum. The xiphoid procedure provides an attachment site for the diaphragm, the most vital muscle that respiration, and also the abdominal muscular consisting of the external oblique, interior oblique, transversus abdominis, and also rectus abdominis muscles.


Physiologic Variants

Usually, females have a shorter and thinner body the the sternum when contrasted to males.

Anatomic Variations

There are plenty of variations in the sternum that generally exist. Variations room most typical in the distal-most an ar of the sternum. Among the many prevalent sternal sports is the bifid xiphoid.

Anatomical variations of the sternal angle likewise exist, for example, the sternal angle can be misplaced bring about inaccurate count of the ribs and thereby causing errors on physical examination the the chest and also procedural errors throughout nerve blocks and needle thoracostomies. Also, a misplaced sternal angle deserve to increase the hazard of sternal fracture in blunt chest trauma. Sometimes second sternal symphysis “angle” deserve to exist, i beg your pardon on imaging studies can mimic a sternal fracture, traumatic fissure or osteolytic lesion.<6>

Another congenital defect of the anterior chest wall surface is the sternal cleft, which results from the fail of midline combination of the sternum. Relying on the level of separation, the sternal cleft deserve to be complete or incomplete. The sternal cleft leaves the heart and an excellent vessels unprotected and also exposed. A small sternal cleft deserve to be even mistaken because that a sternal fracture which is one more reason why this slit is that clinical significance.<6><7>

Incomplete blend of the cartilaginous sternal model can lead come the formation of a circular shaped sternal foramen.<8> This anomaly need to not it is in mistaken because that an abnormality throughout imaging researches of the thorax. Radiologists and surgeons need to be fine versed in the anatomical sports of the sternum. Moreover, the absence of awareness the the sternal foramen is a topic of problem for the forensic pathologist or anthropologist during the forensic check of skeletal remains.


Surgical Considerations

The sternum renders up among the most crucial landmarks used by surgeons for various procedures.

Median Sternotomy: Sternotomy is considered the benchmark incision for cardiac surgery.<9> The average sternotomy is taken into consideration a common an essential incision by which the surgeon splits the sternum follow me the mean plane, permitting the operated doctor to have a better view the the heart, great vessels, and the lungs. It is taken into consideration the most typical osteotomy carry out worldwide.<2>

Sternal Aspiration and Sternal Biopsy: These are procedures embraced to collect specimens that bone marrow indigenous the sternum. The sternum is a commonly used website for arsenal of bone marrow due to the fact that sternal hematopoietic marrow stubborn throughout life.<2> check of bone marrow is typically indicated for the diagnosis the blood dyscrasias and also metastatic cancer.


Clinical Significance

Sternal Malformations/Defects


Cleft sternum
Pectus excavatum

Other Issues

Forensic file of the Sternum

Examination of skeletal continues to be for forensic purposes may incorporate the examination of the sternum. Frequently the forensic pathology or osteologist aims to develop the forensic identity, i m sorry primarily includes ethnicity, sex, age, and also stature, the an individual from the skeletal stays subjected for examination. Stature estimation from the sternum is a relatively new trend under research when contrasted to period estimation and sex determination from the sternum. However, not lot is published on the decision of ethnicity native the sternum. Forensic anthropological studies are population-specific, and also various research studies on forensic identification of the sternum are conducted concerning specific populations worldwide.


Sex determination from the sternum
Age estimate from the sternum

Forensic effects of Sternal Bone Marrow Aspiration Fatalities

A operation procedure-related fatality is a medicolegal fatality that requires more investigation. In such cases, a meticulous forensic autopsy is necessary. A forensic autopsy situation report exists documenting a death from hemorrhage because of an iatrogenic penetrating injury of the thoracic aorta second to the procedure that bone marrow aspiration native the sternum.<36> Ultrasound-guided sternal bone marrow aspiration should be considered to minimization the risk of untoward events of deadly cardiovascular injury.

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<37> Utmost precautions need to be very closely taken to avoid any kind of uncalled because that allegations of clinical negligence.