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


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Anatomy, Thorax, Sternum

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

Author Information

Introduction

The sternum is a partly 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 connect the ribs via the costal cartilages forming the anterior rib cage. The manubrium is the broad superior segment, the human body is the middle portion, and the xiphoid process is a narrow distal segment developing the partial T-shape. The anatomical position and also variations make the sternum crucial bony structure of operation significance. In enhancement to the anatomy that the sternum, clinical and forensic ramifications of the sternum are also 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 exceptional segment that the manubrium sterni. On either side, the left and also right clavicular notches are present. The clavicular notches that the sternum articulate through the medial finish of every clavicle to form the sternoclavicular joints. The manubrium sterni also articulates through the costal cartilages the the first pair that ribs. 
The xiphoid procedure (xiphisternum/xiphoid) is triangular shaped and also forms the distal-most component of the sternum. The size and shape the the xiphoid process are very variable. That is mainly cartilaginous until the age of 40 and also becomes completely calcified by the age of 60. However, these age-related alters in the adult xiphoid procedure are likewise highly variable.
The sternal angle is the projection created by the junction between the manubrium sterni and also the human body of the sternum. This two components of the sternum lie in slightly various planes resulting in the angulation. This angle coincides anteriorly come the intervertebral disc between the 4th and fifth thoracic vertebrae. This edge is additionally known together the edge of Louis.
The sternum"s primary duty is to safeguard the underlying mediastinum and its contents from injury. 

Embryology

During the 6th developmental week of fetal life, the sternum creates independently from a pair of sternal bands called “sternal bars” which space concentrations of mesenchymal cell on either side of the midline.<3> by the 10th week of intrauterine life, these 2 sternal bands arise from the parietal layer of the lateral plate mesoderm bilaterally, climate convert into pre-cartilaginous structures that migrate and fuse in a craniocaudal direction to kind the sternal plate. In the 7th main of intrauterine life, the mesenchyme condenses resulting in the formation of the main cartilaginous version of the three sternal segments (manubrium sterni, the body of the sternum and also the xiphoid process). The cartilaginous sternal model is composed of six horizontal departments known as sternebrae. The superior-most sternebra and also the inferior-most sternebra ultimately represent the manubrium sterni and xiphoid process, respectively. The four sternebrae the lie in between represent the human body of the sternum.<3> The first part the the sternum to type 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 obtained from the medial horizontal branches of the right and also left inner thoracic arteries i m sorry originate straight from the an initial part the the subclavian arteries bilaterally or occasionally originate from a usual trunk. The internal thoracic artery provides off sternal, anterior intercostal, perforating and also non-collateral branches. Sternal branches that the inner thoracic arteries which are the main branches giving the sternum space primarily located in the intercostal spaces. Not just sternal branches but also perforating branches show up to contribute to the sternal blood supply.<4><5>

The blood supply of the sternum has a significant role in the process of healing adhering to sternotomy procedures.<4> that is additionally important to understand the blood supply of the sternum as sternal infections are not uncommon adhering to the harvest the the internal thoracic artery because that coronary artery bypass grafting.<5>

For the venous drainage, the inner thoracic veins drain into the brachiocephalic vein on each side.


Muscles

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


Physiologic Variants

Usually, females have actually a much shorter and thinner body of the sternum when compared to males.

Anatomic Variations

There are countless variations in the sternum that commonly exist. Variations room most usual in the distal-most an ar of the sternum. Among the many prevalent sternal variations is the bifid xiphoid.

Anatomical sports of the sternal angle likewise exist, for example, the sternal angle can be misplaced causing inaccurate counting of the ribs and also thereby leading to errors on physics examination that the chest and procedural errors throughout nerve blocks and also needle thoracostomies. Also, a misplaced sternal angle have the right to increase the hazard of sternal fracture in blunt chest trauma. Sometimes second sternal symphysis “angle” have the right to exist, i m sorry on imaging studies deserve to mimic a sternal fracture, traumatic fissure or osteolytic lesion.<6>

Another congenital defect that the anterior chest wall surface is the sternal cleft, which outcomes from the fail of midline combination of the sternum. Depending on the degree of separation, the sternal cleft can be complete or incomplete. The sternal cleft pipeline the heart and good vessels unprotected and exposed. A narrow sternal cleft deserve to be also mistaken because that a sternal fracture i m sorry is another reason why this slot is that clinical significance.<6><7>

Incomplete combination of the cartilaginous sternal model have the right to lead come the development of a circular shaped sternal foramen.<8> This anomaly need to not it is in mistaken because that an abnormality during imaging researches of the thorax. Radiologists and also surgeons must be well versed in the anatomical sports of the sternum. Moreover, the lack of awareness the the sternal foramen is a subject of issue for the forensic pathologist or anthropologist throughout the forensic examination of bones remains.


Surgical Considerations

The sternum renders up among the most necessary landmarks supplied by surgeons for various procedures.

Median Sternotomy: Sternotomy is considered the benchmark incision because that cardiac surgery.<9> The median sternotomy is considered a common an important incision through which the surgeon splits the sternum along the typical plane, permitting the surgeon to have a much better view of the heart, an excellent vessels, and also the lungs. That is taken into consideration the most common osteotomy carry out worldwide.<2>

Sternal Aspiration and Sternal Biopsy: These are procedures adopted to collect specimens that bone marrow native the sternum. The sternum is a frequently used website for collection of bone marrow since sternal hematopoietic marrow stubborn throughout life.<2> examination of bone marrow is generally indicated because that the diagnosis the blood dyscrasias and also metastatic cancer.


Clinical Significance

Sternal Malformations/Defects


Cleft sternum
Pectus excavatum

Other Issues

Forensic profile of the Sternum

Examination that skeletal remains for forensic purposes may include the examination of the sternum. Frequently the forensic pathology or osteologist intends to develop the forensic identity, i m sorry primarily includes ethnicity, sex, age, and stature, the an separation, personal, instance from the skeletal continues to be subjected because that examination. Stature estimation from the sternum is a relatively new trend under research when compared to period estimation and also sex decision from the sternum. However, not lot is released on the decision of ethnicity indigenous the sternum. Forensic anthropological studies are population-specific, and also various studies on forensic to know of the sternum are conducted concerning details populations worldwide.


Sex determination from the sternum
Age estimation from the sternum

Forensic implications of Sternal Bone Marrow Aspiration Fatalities

A surgical procedure-related fatality is a medicolegal death that requires more investigation. In together cases, a meticulous forensic autopsy is necessary. A forensic autopsy instance report exist documenting a fatality from hemorrhage because of an iatrogenic penetrating injury the the thoracic aorta an additional to the procedure that bone marrow aspiration from the sternum.<36> Ultrasound-guided sternal bone marrow aspiration must be taken into consideration to minimization the hazard of untoward occurrences of deadly cardiovascular injury.

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<37> Utmost precautions have to be very closely taken to avoid any type of uncalled for allegations of clinical negligence.