The term “flail chest” has typically been used to describe a biomechanically unstable chest wall following a traumatic injury. This results in a pathological degree of instability such that normal respiratory mechanics are interfered with: paradoxical respiration is often the result. This occurs during normal inspiratory effort, when, as a negative intrathoracic pressure is produced, the unstable chest wall collapses or caves in, rather than expands (Fig. 1.2). This compromises respiratory function and gas exchange. There is no generally accepted standard definition of a flail chest: it ranges from a minimum of two segmental fractures of adjacent ribs to as many as four segmental fractures of adjacent ribs [5–7]. For the purposes of defining this injury for research, clinical trials, and other studies, we have used the following definition of flail chest:

It is very difficult to break a bony ring (such as the pelvic ring or the rib cage) at only one spot; therefore, most fractures of a circular bony structure tend to occur at two sites. This is also the case for rib fractures. Although a number of different fracture patterns can be seen, typically, one fracture site is displaced and the rib “hinges” or deforms without translational displacement at the other site. This is important clinically, as often only the displaced fracture site needs to be reduced and stabilized: this corrects the angular deformity at the “hinge” site, which is intrinsically stable. This is discussed further in Chaps. 6 and 9 and is a principle by which unnecessary dissection can be avoided. Of course, if both fractures are displaced and unstable, they must both be stabilized [8]. The sternum may represent a separate site of injury and produces the same biomechanical effect as a displaced rib fracture. Fortunately, there is abundant experience with sternal fixation in the cardiac surgery realm, and specialized plates and instruments are available. Additionally, a number of other patterns can have a similar negative clinical effect as a standard flail chest and may represent operative indications, including:

The traumatic force delivered to the chest wall in an injury of this nature typically produces instability and deformity, which has both short-term and long-term consequences for the patient [9–11]. This deformity can be static or fixed, as demonstrated in the computerized tomography (CT) scan depicted in Fig. 1.3, with severe, fixed loss of chest wall contour, loss of thoracic cage volume, and subsequent interference with respiratory function. It must be remembered that the chest wall and rib cage are in constant motion during the ventilatory process, and associated deformity or instability can be dynamic in nature. In some cases, when static deformity may not be severe, the primary manifestation of chest wall instability can be incapacitating pain for the patient. In this situation, it may be difficult or impossible to wean a patient from mechanical ventilation. Mechanical instability of the chest wall can result in severe pain, the requirement for heavy sedation and analgesia, resultant respiratory depression, poor respiratory toilet, and a progressive downward spiral of prolonged mechanical ventilation and the potential complications therein. An example is demonstrated in Fig. 1.4, depicting a young patient with severe chest wall pain following a left-sided chest wall injury. Reduction and fixation of the patient’s rib fractures resulted in an immediate decrease in narcotic medication requirement and rapid weaning and extubation. There is increasing evidence that this type of early primary fixation of multiple rib fractures may be superior to nonoperative treatment [12–15].