Direct compression causes rib and sternal fractures (128). Fractures indicate energy dissipation of the applied force (129). The weakest point of the chest wall is along its lateral aspect (128). Typical fracture patterns emerge depending on the site of compression: anterior compression—sternal and anterolateral rib fractures; posterior compression— posterior rib fractures; and lateral force—posterior fractures and costochondral disruption (128). Older individuals, because of osteoporosis and decreased musculature, are more likely to sustain chest wall fractures following injury (128,130-133). Chest wall fractures in children indicate a high degree of force (e.g., motor vehicle collision) applied to relatively more elastic ribs (128,134).
Because chest wall trauma can contribute to death directly or indirectly, the autopsy examination is not limited simply to the dissection of organs, but the integrity of the chest wall must also be inspected (Fig. 28).
Contiguous fractures, involving at least three ribs and having two fracture sites along each of the affected ribs, create a loose segment that moves paradoxically with respiration ("flail chest" [128,135]). Fractures of any part of the thorax can lead to flail chest (128,136). A transverse sternal fracture enhances paradoxical movement (135). Posterior rib fractures are better supported by back muscles and the scapulae (135). Flail chest is complicated by respiratory insufficiency and, if the trauma victim is hospitalized, atelectasis and consequent pneumonia can develop (128,135,137-139).
The distribution and extent of rib fractures provide information about the direction of force, the relative severity of the applied force, and the presence of underlying visceral injuries (128,136,139,140). Visceral injuries are not invariably accompanied by chest wall fractures, particularly in young individuals (140). A sternal fracture points to mediastinal trauma. Lower rib fractures are a sign of diaphragmatic and abdominal organ injuries. Three or more rib fractures is associated with an increasing risk of visceral trauma and mortality (130,141). A clinical review of 1490 patients admitted with blunt chest injuries showed a mortality rate of 4.7% in those with more than two rib fractures and 17% in patients with flail chest (131). When compression overcomes the integrity of the chest wall (thoracic stability limit), then collapse and considerable visceral injuries result (6). Based on cadaver studies, the "limit" is at least six rib fractures (see ref. 6 and Subheading 6.5.).
Hemothorax and pneumothorax are common findings when chest wall fractures are observed (137,140,141). The risk of these complications rises when the number of rib fractures increases (131,139). Pneumothorax is caused by lung laceration. Hemothorax is commonly caused by lung, heart, and great vessel trauma (see Subheadings 6.4.2., 6.5.-6.7. and ref. 140).
During the examination of the chest cavity, the pathologist must not only document any fractures, but also realize that injury to intercostal vessels is another source of of hemothorax (142). Hemothorax following rib fractures can be delayed (143-146). The usual source of bleeding is from an intercostal artery (143-145). Delayed hemorrhage may occur during a period of clinical improvement when deep breathing and coughing increase chest movement (144). Rarely, no rib fractures are present (145). Failure to examine the sternum, separated from the chest during the autopsy, means that an internal mammary artery or vein tear can be missed (Fig. 29). This is a rare injury (147,148). It is also associated with clavicle or rib fractures (149). Sudden deceleration can avulse the internal mammary artery from its origin at the subclavian artery. The consequent hemothorax or mediastinal hematoma leads to shock in a few hours (147,149,150).
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