Flail chest is defined as

• A. Segment of ribs broken causing paradoxical movement
• B. A mild chest contusion
• C. A tear in the pleural lining
• D. A collapsed lung due to air in pleural space

Answer: (A)

Flail chest is defined by a segment of the chest wall that becomes unstable due to fractures of two or more adjacent ribs in two or more places, creating a floating portion that moves paradoxically—opposite to the rest of the chest during breathing. This paradoxical movement is the defining feature and leads to impaired ventilation and increased work of breathing, often with underlying lung contusion.

This differs from a mild chest contusion, which is just a bruise without chest wall instability. A tear in the pleural lining would cause pneumothorax, an air in the pleural space, not the multiple-rib instability seen in flail chest. A collapsed lung due to air in the pleural space describes pneumothorax, which is a different injury and can occur with or without flail chest but is not the definition of it.