Real-world experience of the role of 18F-fluorodeoxyglucose positron emission tomography/CT refractory fracture-related infection on lower limbs : a retrospective diagnostic study.

Aims: This study aims to evaluates the diagnostic accuracy of F-FDG positron emission tomography (PET)/CT for refractory fracture-related infections (FRIs) in the lower limbs, identifying optimal maximum standardized uptake value (SUVmax) thresholds and analyzing sub-group-specific diagnostic performance.

Methods: This retrospective study included 429 PET/CT scans performed between November 2016 and October 2021 at a tertiary orthopaedic centre. Patients with suspected refractory FRI, characterized by infection persisting after at least two prior treatments, were included. The reference standard combined intraoperative findings, histological analysis, microbiological cultures, and follow-up data. Diagnostic performance metrics, including sensitivity, specificity, and area under the curve (AUC), were calculated using receiver operating characteristic curve analysis. Sub-group analyses stratified patients based on symptomatic presentation and the interval since previous surgery.

Results: PET/CT demonstrated robust diagnostic performance with an overall AUC of 0.84. The optimal SUVmax threshold was 4.75, yielding sensitivity of 70.7% and specificity of 85.6%. Sub-group analyses revealed that tailored thresholds improved diagnostic accuracy, with the 'No signs + Early phase' group achieving the highest accuracy (87.5%) and specificity (89.4%) at a threshold of 5.05. Conversely, a stricter cut-off of 3.95 in the 'No signs + Over phase' group minimized overdiagnosis by distinguishing residual metabolic activity from infection. The 'Over phase' group exhibited the highest specificity (90.1%) at a cut-off of 4.65 but also the highest false-positive rate (42.45%), reflecting the challenges of diagnosing chronic infections. These findings emphasize the variability in SUVmax thresholds across different clinical settings.

Conclusion: F-FDG PET/CT is a reliable diagnostic tool for refractory FRI, with stratified SUVmax thresholds improving diagnostic accuracy based on the time since previous surgery and symptom presentation. Despite its high initial cost, PET/CT demonstrates long-term cost-effectiveness by improving infection management and reducing recurrence rates.