Flail chest is a serious breach of the integrity of the rib cage when at least three ribs are broken in two or more places. Instead of rigidly holding the normal shape of the chest, as the ribcage is meant to do, flail chest results in a segment of the chest wall flailing back and forth in the opposite direction of the rest of the chest wall (what’s known as paradoxical movement).
Flail chest can occur due to a very serious accident, such as a motor vehicle crash. This is a dangerous injury to the ribs that requires emergency medical treatment.