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Flail Chest Definition
Flail chest is an injury associated with the rib cage. It is known as rib fractures in at least four consecutive costals ipsilaterally. The fractures must be in at least two places to create fragments. These segments then move independently of the rib cage.

Causes
A flail chest occurs by blunt force trauma to the thoracic cavity in any direction causing costal fractures in at least two segments, instead of a single fracture that is commonly seen. This can be caused by a significant fall, car accident or other forceful accidents. In the elderly, it can be caused by deterioration of bone, although rare. In children, the majority of flail chest injuries can be a result of the common blunt force traumas or metabolic bone diseases, one known as osteogenesis imperfecta.

Paradoxical Movement
Pulmonary contusions are commonly associated with flail chest and that can lead to respiratory failure. This is due to the paradoxical motions of the chest wall from the fragments interrupting normal breathing and chest movement. Paradoxical motion is when the chest wall projects out during expiration and depresses in during inspiration. This movement can be fatal because since the chest cannot expand correctly when inhaling it cannot take in the proper amount of air needed for the body. Typical paradoxical motion is associated with stiff lungs, which requires extra work for normal breathing, and increased lung resistance, which makes air flow difficult. The respiratory failure from the flail chest requires mechanical ventilation and a longer stay in an intensive care unit. It is the damage to the lungs from the flail segments that are life-threatening.