Flail chest is a life-threatening medical condition that occurs when a segment of the rib cage breaks due to trauma and becomes detached from the rest of the chest wall. Two of the symptoms of flail chest are chest pain and shortness of breath. It occurs when multiple adjacent ribs are broken in multiple places, separating a segment, so a part of the chest wall moves independently. The number of ribs that must be broken varies by differing definitions: some sources say at least two adjacent ribs are broken in at least two places, some require three or more ribs in two or more places. The flail segment moves in the opposite direction to the rest of the chest wall: because of the ambient pressure in comparison to the pressure inside the lungs, it goes in while the rest of the chest is moving out, and vice versa. This so-called "paradoxical breathing" is painful and increases the work involved in breathing. Flail chest is usually accompanied by a pulmonary contusion, a bruise of the lung tissue that can interfere with blood oxygenation. Often, it is the contusion, not the flail segment, that is the main cause of respiratory problems in people with both injuries. Surgery to fix the fractures appears to result in better outcomes. Signs and symptoms Two of the symptoms of flail chest are chest pain and shortness of breath. The characteristic paradoxical motion of the flail segment occurs due to pressure changes associated with respiration that the rib cage normally resists: During normal inspiration, the diaphragm contracts and intercostal muscles pull the rib cage out. Pressure in the thorax decreases below atmospheric pressure, and air rushes in through the trachea. The flail segment will be pulled in with the decrease in pressure while the rest of the rib cage expands. During normal expiration, the diaphragm and intercostal muscles relax increasing internal pressure, allowing the abdominal organs to push air upwards and out of the thorax. However, a flail segment will also be pushed out while the rest of the rib cage contracts. Paradoxical motion is a late sign of flail segment; therefore, an absence of paradoxical motion does not mean the patient does not have a flail segment. The constant motion of the ribs in the flail segment at the site of the fracture is extremely painful, and, untreated, the sharp broken edges of the ribs are