**2. Background**

Median sternotomy was originally introduced by Milton in 1897 and was performed infrequently for various conditions of the mediastinum until cardiac surgery as a field blossomed in the 1950s [17]. Shumacker first suggested median sternotomy as the procedure of choice for approaches to the heart and great vessels [18] since it avoided the significant pain and other complications, primarily pulmonary- or pleural-based, of the bilateral anterior thoracotomy ("clamshell") incision, which was most frequently used up to that point. However, not until Julian and colleagues demonstrated discrete advantages of the median sternotomy incision for cardiac surgery, particularly improved surgical efficiency, excellent exposure the heart, great vessels, and pulmonary hila, and reduced pulmonary trauma, was a convincing argument for median sternotomy as the incision of choice for cardiac surgical procedures put forth [19 Table 1]. The utility of this incision, the ease and speed of performance, and the common nature of surgically-treated cardiovascular and

Sternal Wound Complications Following Cardiac Surgery 285

comparing different treatment modalities for sternal wound infection, it is important to be

Two prominent classification schemes have been proposed and are in use. Mediastinal dehiscence or the more chronic form, sternal nonunion, is defined as sternal wound disruption without any evidence for infection either clinically or pathologically [23, 24]. These entities will not be discussed in any detail. In contrast, mediastinitis, as characterized by the U.S. Centers for Disease Control and Prevention (CDC), is an infection of the mediastinum diagnosed by isolation of pathogenic organisms from the mediastinal fluid or tissue especially when there is obvious evidence of infection at the time of sternal exploration [25]. Alternatively, a combination of clinical features including chest pain, sternal drainage with bony instability, fevers, radiographic findings such as widened mediastinum, and bacterial isolation may also warrant a diagnosis of mediastinitis. Obviously, from the surgical perspective, these definitions are somewhat lacking since either superficial infections, confined to the soft tissues, or deep infections, involving the bone and/or retrosternal space could produce bacteremia and clinical signs of severe

Fortunately, more descriptive classification schemes have been introduced and provide more specific insight into the pathologic involvement of the sternal tissues and the clinical consequences and course [23, 26, 27]. For example, the classification scheme introduced by El Oakley and Wright is based on the time at which the patient presents with mediatiastinitis relative to the initial surgical procedure [23]. Schulman et al have advocated a similar classification system [27]. In addition, the El Oakley description also accounts for relevant risk factors underlying the clinical scenario and whether or not previous attempts to treat the sternal wound infection have been made and failed [Table 2]. Therefore, five distinct categories of infection are described, each with important treatment implications. For example, the subtypes I and II appear to respond well to primary sternal closure with mediatinal irrigation, while subtypes III-V appear to require more aggressive sternal

Type 1 Mediastinitis within 2 weeks of operation

Type 2 Mediastinitis between 2 and 6 weeks of

Type 5 Mediastinitis presenting 6 weeks or more

Table 2. Classification scheme of mediastinitis introduced by El Oakley and Wright based on the time at which the patient presents with mediatiastinitis relative to the initial surgical

Type 3a Type 1 with one or more risk factors Type 3b Type 2 with one or more risk factors Type 4a Type 1, 2, or 3 after one failed therapy Type 4b Type 1, 2, or 3 after more than one failed

without risk factors

therapy

after operation

operation without risk factors

clear about the extent of infection, since heterogeneity could skew reported results.

infection [23].

debridement and repair techniques [23].

procedure (modified from El Oakley and Wright [23]).

Classification Description of Infection


Table 1. Comparison of exposure of various intrathoracic anatomic structures through median sternotomy, right thoracotomy, or left thoracotomy. (+++ denotes excellent, reliable exposure; 0 denotes no reliable exposure)

thoracic diseases in multiple populations approached through this incision are factors which combine to make median sternotomy the most commonly performed osteotomy worldwide [20]. Recently, several alternatives to median sternotomy have been promoted, including thoracoscopic and robotic approaches to cardiac and thoracic procedures [21, 22]. These approaches are possible as a result of high fidelity instrumentation and video platforms but are limited by steep learning curves and expense. Therefore, for most hospital systems performing cardiac surgical procedures, median sternotomy remains the mainstay incision.
