Sternal Dehiscence

• General considerations
  
  
• Follows median sternotomy usually for cardiothoracic surgery
• Defined as complete separation of the sternum
• Frequently associated with sternal wound infection, most often by S. aureus
• May or may not be associated with mediastinitis
• Definitions for post-sternal mediastinitis and sternal wound infection vary, some including clinical findings only, some requiring microbiological confirmation
• Incidence has been reported in 4.5% of coronary artery bypass graft (CABG) surgery
• While diagnosis is usually made clinically, imaging plays a key role in either initial diagnosis and/or confirmation of the clinical diagnosis
• Females are at greater risk than male
• Risk factors
• Hypertension
• Smoking
• COPD
• Obesity
• Diabetes
• Prolonged bypass time
• Prolonged post-operative support on ventilators
• Re-operation
• Clinical findings
• Pain
• Most incisional pain normally subsides over first month
• Fever
• “Clicking” sound from the sternum
• Imaging findings
• Originally it was thought that a mid-sternal stripe of lucency seen on frontal chest radiographs was an indicator of sternal dehiscence but this is now felt to be of little diagnostic value
• With dehiscence, sternal wires are displaced to one side or the other as they tend to pull through the sternum, rather than break
• Most frequently 2 cm of displacement is seen in 2 or more wires
• Sternal wire breaks alone are not an indicator of sternal dehiscence and single breaks are usually of no clinical significance
• CT findings of mediastinitis can include small air bubbles or an air-fluid level in a mediastinal collection
• Treatment
• Wide debridement of devitalized infected soft tissue and bone
• Culture-specific antibiotics
• Flap closure (e.g., muscle, musculocutaneous, omentum) for best wound healing
• Prognosis
• While mortality rate has dropped, it is still significant
• Had been reported as high as 25%
• Mortality rate from sternal wound dehiscence has now dropped to less than 10%

Sternal dehiscence. The blue arrows point to one group of sternal wires that are displaced to the right of the midline while the red arrow points to a lower wire that has traveled with the left half of the dehisced sternum (see below). Normally, the sternal wires should align in the midline. The black arrow points to a prosthetic aortic valve.

For the same photo without the arrows, click here

Axial CT images of Sternal Dehiscence. Four axial contrast-enhanced CT images of the chest are shown, from highest (top left) to lowest (bottom right). The sternum has separated (white arrow) with some of the wires attached to the right half (blue circles) and one of the wires attached to the left half (red circle). There is a fluid collection between the two halves of the sternum (green arrow).
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Wandering Wires: Frequency of Sternal Wire Abnormalities in Patients with Sternal Dehiscence  American Journal of Roentgenology, Vol 173, 777-780 Phillip M. Boiselle, Alberto V.  Mansilla, Mary S. Fisher, Theresa C. McLoud