UPDATED:The sternal angle is the term used to denote the angulation at the joint between the manubrium and the body of the sternum. This transverse joint is called the "manubriosternal joint" and is a secondary cartilaginous joint of a type known as a symphysis. The angle varies between 160 and 169 degrees.
It is know eponymously as the "angle of Louis" named after Antoine Louis1 (1723-1792), a French physician. The importance of the sternal angle is that of an anatomical superficial landmark, which forms a horizontal plane which indicates a series of anatomical occurrences, as follows:
• Location of the cartilages of the second rib
• Beginning and end of the aortic arch
• Boundary between the inferior and superior mediastinum
• Location of the bifurcation of the trachea
• Posteriorly, the plane of the sternal angle passes trough the T4-T5 intervertebral disc (sometimes a little lower, through the superior aspect of T5)
• Highest point of the pericardial sac.
• It is the point where the right and left pleurae meet in the midline. They touch, but their pleural spaces do not communicate.
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1. Some authors contest the eponym, adjudicating it to Pierre Charles Alexander Louis (1787-1872), another French physician.
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