Paradoxical motion of the chest wall occurs in which of the following injuries?

• A. Barrel chest
• B. Flail chest
• C. Funnel chest
• D. Pigeon chest

Answer: (B)

Paradoxical motion of the chest wall occurs when a portion of the rib cage becomes unstable and moves opposite to the rest of the chest during breathing. This happens with a flail chest, where multiple adjacent ribs are fractured in two or more places, creating a free-floating segment. During inspiration, the healthy chest expands while the flail segment is pulled inward by the negative intrathoracic pressure; during expiration, it moves outward with the positive pressure. This opposite movement impairs ventilation and can worsen oxygenation, often alongside underlying lung injury. The other terms describe chest-wall deformities that change shape but do not produce this paradoxical inward–outward motion: barrel chest is an increased anterior–posterior diameter from hyperinflation, funnel chest is a sunken sternum (pectus excavatum), and pigeon chest is a protruding sternum (pectus carinatum).