What is paradoxical movement in flail chest?

In flail chest, paradoxical movement refers to the abnormal motion of a section of the rib cage that has become separated from the rest of the thoracic wall due to multiple rib fractures. In this condition, the flail segment moves in the opposite direction to the normal chest wall during respiration.

During inspiration, when the diaphragm contracts and negative pressure in the thoracic cavity typically causes the chest to expand, the flail segment instead moves inward. This inward movement occurs because the chest wall surrounding it expands, leaving the flail segment to collapse inward due to the lack of supportive structural integrity from the ribs. Conversely, during expiration, when the chest normally compresses and the diaphragm relaxes, the flail segment moves outward. This is a paradoxical response and is a hallmark of flail chest, illustrating the loss of coordinated movement in the thoracic wall, which is critical for effective breathing.

Understanding this principle is essential for recognizing the clinical implications of flail chest, which can compromise breathing and lead to respiratory distress, necessitating careful management.