Final answer:
Flail chest is the injury that leads to paradoxical motion, where a segment of the rib cage moves opposite to the normal direction due to trauma that causes multiple rib fractures.
Step-by-step explanation:
The kind of injury that leads to paradoxical motion affecting a person's chest is D) Flail Chest.
Paradoxical motion, also known as flail chest, occurs when a segment of the rib cage breaks due to trauma and becomes detached from the rest of the chest wall. This condition is characterized by the abnormal movement of the affected segment that moves inwards during inhalation and outwards during exhalation, opposite to the normal chest wall movements. This is due to multiple adjacent ribs being fractured in multiple places, typically as a result of a strong blow to the chest, such as from a vehicle accident or a fall. As the rigidity and stability of the thoracic cage are compromised, the area of the chest wall affected by the flail chest will not contribute effectively to lung expansion, leading to inadequate ventilation and potential respiratory distress.
Clavicle breaks, hemopneumothorax, and tension pneumothorax are other forms of chest injuries but they do not result in paradoxical motion like flail chest does.