Abstract
Purpose18F-Fluorodeoxyglucose positron emission tomography (18F-FDG PET/CT) is frequently used to diagnose fracture-related infections (FRIs), but its diagnostic performance in this field is still unknown. The aims of this study were: (1) to assess the diagnostic performance of qualitative assessment of 18F-FDG PET/CT scans in diagnosing FRI, (2) to establish the diagnostic performance of standardized uptake values (SUVs) extracted from 18F-FDG PET/CT scans and to determine their associated optimal cut-off values, and (3) to identify variables that predict a false-positive (FP) or false-negative (FN) 18F-FDG PET/CT result.MethodsThis retrospective cohort study included all patients with suspected FRI undergoing 18F-FDG PET/CT between 2011 and 2017 in two level-1 trauma centres. Two nuclear medicine physicians independently reassessed all 18F-FDG PET/CT scans. The reference standard consisted of the result of at least two deep, representative microbiological cultures or the presence/absence of clinical confirmatory signs of FRI (AO/EBJIS consensus definition) during a follow-up of at least 6 months. Diagnostic performance in terms of sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) was calculated. Additionally, SUVs were measured on 18F-FDG PET/CT scans. Volumes of interest were drawn around the suspected and corresponding contralateral areas to obtain absolute values and ratios between suspected and contralateral areas. A multivariable logistic regression analysis was also performed to identify the most important predictor(s) of FP or FN 18F-FDG PET/CT results.ResultsThe study included 156 18F-FDG PET/CT scans in 135 patients. Qualitative assessment of 18F-FDG PET/CT scans showed a sensitivity of 0.89, specificity of 0.80, PPV of 0.74, NPV of 0.91 and diagnostic accuracy of 0.83. SUVs on their own resulted in lower diagnostic performance, but combining them with qualitative assessments yielded an AUC of 0.89 compared to an AUC of 0.84 when considering only the qualitative assessment results (p = 0.007). 18F-FDG PET/CT performed <1 month after surgery was found to be the independent variable with the highest predictive value for a false test result, with an absolute risk of 46% (95% CI 27–66%), compared with 7% (95% CI 4–12%) in patients with 18F-FDG PET/CT performed 1–6 months after surgery.ConclusionQualitative assessment of 18F-FDG PET/CT scans had a diagnostic accuracy of 0.83 and an excellent NPV of 0.91 in diagnosing FRI. Adding SUV measurements to qualitative assessment provided additional accuracy in comparison to qualitative assessment alone. An interval between surgery and 18F-FDG PET/CT of <1 month was associated with a sharp increase in false test results.
Highlights
Study design and eligibility criteriaFracture-related infection (FRI) is a serious complication following trauma surgery and can lead to increased morbidity and high medical costs [1, 2]
Combining the standardized uptake values (SUVs) measurement data with the qualitative assessment of 18F-FDG PET/CT scans in a separate receiver operating characteristic (ROC) curve yielded an area under the curve (AUC) of 0.89 and a diagnostic accuracy of 0.86, in contrast to an AUC of 0.84 and a diagnostic accuracy of 0.83 for the qualitative assessment on its own
The current study showed that qualitative assessment of 18FDG PET/CT scans has good performance in diagnosing FRI with a diagnostic accuracy of 0.83
Summary
Study design and eligibility criteriaFracture-related infection (FRI) is a serious complication following trauma surgery and can lead to increased morbidity and high medical costs [1, 2]. Clinical symptoms are not always evident, diagnosing FRI can be challenging. This problem was worsened by the fact that, until recently, there was no uniform definition of FRI [3]. The AO Foundation (Arbeitsgemeinschaft für Osteosynthesefragen) and the European Bone and Joint Infection Society (EBJIS) published a consensus definition comprising confirmatory and suggestive criteria for diagnosing FRI [4]. Medical imaging is considered to be only an adjunct to the diagnosis of FRI (i.e. a suggestive criterion). The reason for this is that the evidence for its accuracy in diagnosing FRI is limited. We used the same study design to evaluate the diagnostic performance of 18Ffluorodeoxyglucose positron emission tomography/ computed tomography (18F-FDG PET/CT)
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