Following blunt chest trauma, a patient has shallow, painful breathing and the left chest wall collapses in during inhalation and bulges during exhalation. This pattern indicates which injury?

• A. Isolated rib fracture
• B. Pulmonary contusion
• C. Pneumothorax
• D. Flail chest

Answer: (D)

The key idea is that this pattern is a paradoxical chest wall movement after blunt trauma, which defines a flail chest. When several adjacent ribs are fractured in multiple places, a segment of the chest wall becomes detached from the rest of the thorax. Normally, the chest expands outward during inspiration. With a flail segment, that portion moves inward as the person tries to breathe in and then bulges outward as they exhale. That opposing movement makes breathing shallow and painful and impairs ventilation.

This isn’t explained by an isolated rib fracture, which would cause local tenderness without a free-floating chest wall segment. It isn’t a pulmonary contusion, which is damage to lung tissue and presents with signs of lung injury but not paradoxical chest wall motion. It isn’t a pneumothorax, which involves air in the pleural space and signs like diminished breath sounds or hyperresonance, but not a chest wall segment moving paradoxically with respiration.

Because the chest wall is unstable, flail chest can lead to significant respiratory compromise and often requires pain control and respiratory support, sometimes even positive-pressure ventilation, to stabilize the chest from the inside and improve oxygenation.