The ‘Silent’ Fracture-Related Infection: Can F-18 (Fdg) Fluoro Deoxy Glucose - Positron Emission Tomography-Computed Tomography (Pet Ct) Scan AId in Diagnosis?

The clinical presentation of infection complicating fracture fixation is extremely varied, ranging from obvious purulence and exposed implants to subclinical infection with subtle signs and symptoms. Diagnosis of these silent subtle infections is difficult, and a combination of clinical features, radiology, biomarkers and histology is used for making an accurate diagnosis. We looked at the diagnostic utility of F-18 FDG PET CT scans in the diagnosis of late fracture related infection (12 weeks after the index surgery). Patients with metallic trauma implant in situ and ‘suspected’ fracture related infection (AO/ EBJIS criteria) were included in the study. All patients underwent F-18 FDG PET scans prior to surgery necessitated by the suspected infection. PET CT scans were considered positive if increased diffuse 18F-FDG uptake was detected around the implant (especially at the bone–prosthesis interface), or in the surrounding tissue and negative if there was no uptake in the region. Post surgery patients were diagnosed positive for fracture related infection if at least two deep cultures grew the same organism or histopathological analysis showed more than 5 PMN/high power field. The diagnostic utility of the 18F-FDG PET/CT scan in diagnosing FRI was assessed using culture and histopathology as a reference. 17 patients, inclusive of 4 diabetics with metallic trauma implants suspected of fracture related infection underwent a F-18 FDG PET CT scan prior to surgery. 9 patients presented more than a year after the index surgery and 8 patients had an associated fracture non-union along with the suspected infection. 14 patients had FDG tracer uptake suggestive of infection (PET positive), while the remaining 3 patients were PET negative. All 14 PET positive patients were also diagnosed as fracture related infection positive by histopathological criteria. However, only 11 PET positive patients were culture positive with Staph aureus being the most commonly isolated microorganism (n=5). 18 FDG PET CT demonstrated 100 % sensitivity (95% CI : 26.24 −100 %) and 100 % specificity (95 % CI :76.84 −100 %), negative predictive value and positive predictive value of 100 % in detecting fracture related infection in this study 18F-FDG PET/CT scan is useful tool for the diagnosis of fracture related infection associated with a trauma implant especially when clinical presentation is not obvious.