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Background: 18 F-fluorodeoxyglucose ( 18 F-FDG) positron emission tomography (PET)/computed tomography (CT) has proven to have a high diagnostic accuracy for the detection of bone infections. In patients with delayed union it may be clinically important to differentiate between aseptic and septic delayed union. The aim of this study was to evaluate the efficacy and to assess the optimal diagnostic accuracy of FDG-PET/CT in differentiating between aseptic and septic delayed union in the lower extremity., Methods: This is a retrospective study of consecutive patients who underwent FDG-PET/CT scanning for suspicion of septic delayed union of the lower extremity. Diagnosis of aseptic delayed union or septic delayed union was made based on surgical deep cultures following PET/CT scanning and information on clinical follow-up. FDG-uptake values were measured at the fractured site by use of the maximum standardized uptake value (SUV max ). Sensitivity, specificity and diagnostic accuracy of FDG-PET/CT were calculated at various SUV max cut-off points., Results: A total of 30 patients were included; 13 patients with aseptic delayed unions and 17 patients with septic delayed unions. Mean SUV max in aseptic delayed union patients was 3.23 (SD ± 1.21). Mean SUV max in septic delayed union patients was 4.77 (SD ± 1.87). A cut-off SUV max set at 4.0 showed sensitivity, specificity and diagnostic accuracy of FDG-PET/CT were 65, 77 and 70% to differentiate between aseptic and septic delayed union, respectively., Conclusion: Using a semi-quantitative measure (SUV max ) for interpretation of FDG-PET/CT imaging seems to be a promising tool for the discrimination between aseptic and septic delayed union.

Introduction: Fluorine-18 fluorodeoxyglucose (F-FDG) PET/computed tomography (CT) has proven to be a valuable imaging modality with high diagnostic accuracy for the detection of bone infections. However, the physiological uptake values for F-FDG in the long bones of the lower extremity have not been established yet. This hampers correct interpretation of a F-FDG-PET/CT scan., Purpose: The purpose of this study was to determine the physiological uptake values of F-FDG in the long bones of the lower extremities, including the femur and the tibia., Patients and Methods: We retrospectively analyzed the F-FDG-PET/CT scan of 84 consecutive patients from our database. F-FDG uptake parameters included mean standardized uptake value (SUVmean) and maximum standardized uptake value (SUVmax). Both SUVs were determined in the diaphyseal region of the femur and the tibia., Results: SUVmean for the femoral diaphysis was 0.46 [95% confidence interval (CI) 0.42-0.49] and SUVmax was 0.81 (95% CI 0.74-0.88). For the tibial diaphysis, SUVmean was 0.34 (95% CI 0.32-0.37) and SUVmax was 0.61 (95% CI 0.56-0.65). SUVmean and SUVmax of the femur were significantly higher than that of the tibia (both P<0.01). SUVs for men were not significantly different from that for women and did not discriminate between age classes., Conclusion: For a correct interpretation of the F-FDG-PET/CT scan, we have determined the F-FDG uptake values in the long bones of the femur and the tibia. A SUVmean less than 0.5 and a SUVmax less than 0.8 can be considered as normal bone, irrespective of sex or age.