Flail chest is defined as which phenomenon?

• A. Paradoxical movement of a chest wall segment during respiration
• B. Single rib fracture without instability
• C. Pectus excavatum
• D. Spontaneous pneumothorax

Answer: (A)

The key idea here is paradoxical movement of a chest wall segment during breathing. Flail chest occurs when multiple adjacent ribs are fractured in two or more places, creating a free-floating segment that loses contact with the rest of the chest wall. Because of this instability, that segment moves inward with inspiration (as the rest of the chest expands due to negative intrathoracic pressure) and outward with expiration, opposite to the motion of the intact chest. This paradoxical motion is the defining feature.

Other conditions don’t produce this pattern: a single rib fracture without instability doesn’t create a free-floating segment; pectus excavatum is a congenital chest wall deformity; spontaneous pneumothorax is air in the pleural space causing lung collapse, not abnormal chest wall motion.