What is the clinical significance of the sternal angle?

The sternal angle is an anatomical landmark physicians use as a starting point for counting ribs and thoracic vertebrae. It is also used as a landmark for placement of a stethoscope.

The sternal angle is located about 5 centimeters down the bony ridge below the suprasternal notch, which is the indent at the base of the neck between the collar bone. The angle is approximately the same location where the second rib attaches to the sternum. The sternal angle is also called the "Angle of Louis" after Dr. Antoine Louis, a French surgeon in the mid- to late-1700s who invented the guillotine.