Etiology
Rib fractures most commonly result from motor vehicle collisions (MVCs), falls, assaults, and industrial accidents.[8] A flail chest is defined as consecutive, segmental (i.e., multiple fractures in the same rib) ipsilateral rib fractures, classically causing paradoxical motion of the chest wall during inspiration and expiration. These are usually the result of high-energy MVCs with concomitant injuries leading to increased morbidity and mortality.[11] Significant intrusion of the steering column can apply dramatic force to the thoracic cage.
Traumatic fractures can also occur due to cardiopulmonary resuscitation (CPR). In patients receiving external cardiac massage as a form of CPR, rib fractures were caused in 77% of males and 85% of females.[12] However, the incidence of rib fractures following CPR in children, who have a much more flexible chest wall, is estimated to be <2%.[13]
Among infants younger than 12 months presenting with rib fractures, as many as 82% sustained these injuries non-accidentally (i.e., through physical abuse).[2][3] Of all skeletal injuries, rib fractures have the highest likelihood of being the result of physical abuse.[14]
Metastasis from lung, prostate, breast, and liver cancer can also involve the ribs, accounting for 12.6% of metastatic lesions.[15] Furthermore, there are numerous primary bone tumors that can present as pathologic rib fractures, including osteochondroma, enchondroma, plasmacytoma, chondrosarcoma, and osteosarcoma. About 37% of these lesions are malignant.[16] Multiple myeloma can present with rib fractures and even with a flail chest.[17]
Stress fractures can result from severe coughing or athletic activities, such as golfing, swimming, baseball, and competitive rowing.[18][19][20][21] Rib stress fractures occur in 2% to 12% of rowers as a result of cyclic loading to the rib cage.[22]
As age increases, the absolute risk of sustaining a fragility fracture is inversely proportional to the bone mineral density of the patient, with about 27% of these fractures occurring in the ribs.[4]
Pathophysiology
There are 12 ribs on each side of the normal human thorax (24 ribs in total) that function to protect the intrathoracic and upper abdominal organs and to aid in respiration. The first 2 ribs are shorter than ribs 3 through 10 and are intimately associated with the subclavian artery and the brachial plexus. Greater force is required to fracture these 2 ribs than the others, and such fractures should alert the physician to the possibility of vascular or neurologic injury.[23][24][25] Fractures of ribs 3 through 10 can be single, segmental, or multiple. These injuries are the direct result of a significant force, resulting in fracture and often displacement of the rib fragments. As a result, these rib fragments have the potential to injure the thoracic or abdominal viscera. Upper rib injuries tend to injure the lung parenchyma by direct penetration. The presence of multiple rib fractures correlates with an increased incidence of solid organ injury (about 35%).[26]
On the inferior surface of each rib are the intercostal nerve, artery, and vein. This neurovascular bundle has the potential to be injured with fractures of the rib, resulting in hemothorax and substantial pulmonary insufficiency.
Ultimately, rib fractures impair adequate ventilation, resulting in atelectasis, poor oxygenation, and respiratory compromise.[27]
Ribs and costal cartilage are more elastic in children, making substantial force necessary to cause a fracture. Therefore, in the absence of a known traumatic event, nonaccidental trauma should be suspected, as up to 82% of patients in this category are victims of physical abuse.[2][3]
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