stern/o is a combining form that refers to “sternum (breastbone)”.
The sternum or breastbone is a flat, long bone that is positioned in the center of the chest. It is attached to the ribs by cartilage and makes up the front of the rib cage. By doing so, the heart, lungs, and major blood vessels are protected from injury. Similar in shape to a necktie, the sternum is one of the largest and longest in the flat bone in the body.