**6. Diagnosis**

Depending on the virulent nature of the sternal wound infection, patients typically present within 30 days of cardiac surgery. The most common symptoms include sternal wound drainage, sternal instability, fever, and malaise. In many cases, a high index of suspicion is required to establish the diagnosis, especially when classic signs and symptoms are absent. In addition, it is often difficult to distinguish on physical examination the difference between deep sternal wound infection (infection present beneath the sternum) and superficial sternal infection. Therefore, early wound opening and inspection with appropriate sampling of tissue for bacteriologic assessment is strongly encouraged when sufficient clinical suspicion exists.

One of the most reliable signs of DSWI is sternal instability, which frequently implies a deeper problem than can be appreciated at the superficial level [44]. While sternal instability can be tested on physical examination, we have often noted that the patient themselves will typically report sternal clicking with inspiration, cough, or various other physical maneuvers, so this information should be thoughtfully considered if DSWI diagnosis is being entertained.

The use of various radiographic examinations is often encouraged when evaluating for DSWI, and, in fact, is included as part of the CDC guidelines for defining mediastinitis [25]. Formerly, PA and lateral chest radiograph was the investigative procedure of choice, where details such as a "sternal stripe" indicated present of air between the two sternal halves. The lateral displacement of one or more sternal wires, secondary to tearing of the wire through one side of the sternum, has been a frequently noted finding in the case of poststernotomy infection [37]. More recently, chest computed tomography has been suggested as the procedure of choice for assessing sternal wound infection when a diagnosis cannot be established by clinical examination alone [45, 46]. Mediastial fluid collections, free gas bubbles, soft tissue swelling, pleural effusions, sternal dehiscence, and subcutaneous fluid collections have been the predominant CT findings in cases of DSWI [47], but these features appear to be more specific and sensitive for DSWI presenting more than 3 weeks after surgery [48].
