The sternal angle or 'angle of Louis', from the Latin

Latin

Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 angulus Ludovici is the anterior angle formed by the junction of the manubrium

Manubrium

The manubrium or manubrium sterni is the broad, upper part of the sternum. Located ventrally with a quadrangular shape, wider superiorly and narrower inferiorly, it articulates with the clavicles and the first two ribs.-Borders:The superior border is the thickest and presents at its center the...

 and the body of the sternum (the manubriosternal junction) in the form of a secondary cartilaginous joint (symphysis). This is also called the manubriosternal joint or Angle of Louis

Antoine Louis

Antoine Louis was a French surgeon and physiologist who was born in Metz.He was originally trained in medicine by his father, a surgeon-major at a local military hospital. As a young man he moved to Paris, where he served as gagnant-maîtrise at the Salpêtrière...

. The sternal angle is a palpable clinical landmark.

It marks the approximate level of the 2nd pair of costal cartilages and the level of the intervertebral disc

Intervertebral disc

Intervertebral discs lie between adjacent vertebrae in the spine. Each disc forms a cartilaginous joint to allow slight movement of the vertebrae, and acts as a ligament to hold the vertebrae together.-Structure:...

 between T4 and T5. It also marks approximately the beginning and end of the aortic arch

Aortic arch

The arch of the aorta or the transverse aortic arch is the part of the aorta that begins at the level of the upper border of the second sternocostal articulation of the right side, and runs at first upward, backward, and to the left in front of the trachea; it is then directed backward on the left...

, and the bifurcation of the trachea

Vertebrate trachea

In tetrapod anatomy the trachea, or windpipe, is a tube that connects the pharynx or larynx to the lungs, allowing the passage of air. It is lined with pseudostratified ciliated columnar epithelium cells with goblet cells that produce mucus...

 into the left and right main bronchi

Bronchus

A bronchus is a passage of airway in the respiratory tract that conducts air into the lungs. The bronchus branches into smaller tubes, which in turn become bronchioles....

.

It also marks the boundary between the superior and inferior portion of the mediastinum

Mediastinum

The mediastinum is a non-delineated group of structures in the thorax, surrounded by loose connective tissue. It is the central compartment of the thoracic cavity...

.

The angle is approximately 140 degrees (varies depending on normal variation of human anatomy).

It is named after Pierre Charles Alexandre Louis

Pierre Charles Alexandre Louis

Pierre Charles Alexandre Louis was a French physician, known for introducing the use of the "numerical method" in the field of medicine — i.e., the concept that knowledge about a disease, its history, clinical presentation and treatment, could be derived from aggregated patient data.Louis became...

, a French physician of the 19th century, who was one of the first to bring mathematics to medicine, disproving bloodletting as a practice by showing statistically that it did not work.