Figure 1. Anteroposterior radiograph of the right ankle.
Figure 2. Lateral radiograph of the right ankle.
Figure 3. Image of the wound.
A 65-year-old man presents to the emergency department with a draining wound on the medial side of his right ankle. He underwent open reduction and internal fixation of the ankle 3 months ago for a closed fracture of the distal tibia and fibula. He reports continued pain over the right leg that is made worse with weight bearing. He has difficulty controlling his type 1 diabetes. His appearance is disheveled. Anteroposterior and lateral radiographs are obtained (Figures 1 and 2). An image of the wound is shown in Figure 3.
Which preoperative work-up is most accurate for making the diagnosis of an infected nonunion?
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The tibia lies just under the skin and subcutaneous tissue and is relatively superficial compared with other long bones. The incidence of infection and wound-healing problems can be a major concern in high-energy distal tibia fractures due to the thin soft tissue coverage. Once an infection is introduced into the fracture, either from an open wound or a wound contaminant, the bacteria devitalize surrounding tissue and inhibit healing. If an infected nonunion is present, all infected, nonviable tissue including skin, soft tissue, and bone must be removed with surgical debridement. Bacteria have a predilection for metal implants (foreign bodies) and often form a biofilm on the implant that protects the bacteria against antibiotics and the host immune response, which is why all implants must be removed if an infected nonunion is present.1,2
The diagnosis of an infected nonunion is based on several factors including preoperative labs, diagnostic imaging, and tissue culture. The best preoperative predictor of an infected nonunion includes an elevated white blood cell count, erythrocyte sedimentation rate, and C-reactive protein level. When all 3 labs are positive, the predicted probability of infection is 100%. Wound culture results from a superficial swab are unreliable. Bacterial growth on a wound culture may be influenced by prior antibiotic use, which may cause a false negative. A positive superficial wound culture also grows a different bacteria than the one found in the deep infection nearly 50% of time.1,2
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor-in-chief of the Journal of Orthopedics for Physician Assistants (JOPA).
1. Stucken C, Olszewski DC, Creevy WR,Murakami AK, Tornetta P. Preoperative diagnosis of infection in patients with nonunions. J Bone Joint Surg Am. 2013;95(15):1409-1412.
2. Patzakis MJ, Zalavras CG. Chronic posttraumatic osteomyelitis and infected nonunion of the tibia: current management concepts. J Am Acad Orthop Surg. 2005;13(6):417-427.