<unk>  is found in 30–75% of severe cases of chest injury, making it the most common serious injury to occur in association with thoracic trauma. Of people who have multiple injuries with an injury severity score of over 15,<unk>  occurs in about 17%. It is difficult to determine the death rate (mortality) because<unk>  rarely occurs by itself. Usually, deaths of people with<unk>  result from other injuries, commonly traumatic brain injury. It is controversial whether<unk>  with flail chest is a major factor in mortality on its own or whether it merely contributes to mortality in people with multiple injuries. The estimated mortality rate of<unk>  ranges from 14–40%, depending on the severity of the<unk>  itself and on associated injuries. When the<unk> s are small, they do not normally increase the chance of death or poor outcome for people with blunt chest trauma; however, these chances increase with the size of the<unk> . One study found that 35% of people with multiple significant injuries including<unk>  die. In another study, 11% of people with<unk>  alone died, while the number rose to 22% in those with additional injuries.<unk>  is thought to be the direct cause of death in a quarter to a half of people with multiple injuries (polytrauma) who die. An accompanying flail chest increases the morbidity and mortality to more than twice that of<unk>  alone.<unk>  is the most common cause of death among vehicle occupants involved in accidents, and it is thought to contribute significantly in about a quarter of deaths resulting from vehicle collisions. As vehicle use has increased, so has the number of auto accidents, and with it the number of chest injuries. However an increase in the number of airbags installed in modern cars may be decreasing the incidence of<unk> . Use of child restraint systems has brought the approximate incidence of<unk>  in children in vehicle accidents from 22% to 10%. Differences in the bodies of children and adults lead to different manifestations of<unk>  and associated injuries; for example, children have less body mass, so the same force is more likely to lead to trauma in multiple body systems. Since their chest walls are more flexible, children are more vulnerable to<unk>  than adults are, and thus suffer from the injury more commonly.<unk>  has been found in 53% of children with chest injuries requiring hospitalization. Children in forceful impacts suffer twice as many<unk> s as adults with similar injury mechanisms, yet have proportionately fewer rib fractures. The rates of certain types of injury mechanisms differ between children and adults; for example, children are more often hit by cars as pedestrians. Some differences in children's physiology might be advantageous (for example they are less likely to have other medical conditions), and thus they have been predicted to have a better outcome. However, despite these differences, children with<unk>  have similar mortality rates to adults.
Pulmonary contusion
Hemothorax
Pulmonary hematoma
Diaphragmatic rupture
Urinothorax
Hemopneumothorax
Hydropneumothorax
Flail chest