Assessing diagnostic accuracy: 18F-FDG PET-CT scans in low-grade infection detection among post-traumatic long bone non-unions; a literature review and clinical data.

Abstract

The diagnosis of low-grade infection in post-traumatic long bone non-unions poses challenges due to the absence of clinical signs. This study aimed to review the available literature on the diagnostic accuracy of imaging techniques for low-grade infections and assess the diagnostic accuracy of 18F-FDG PET-CT scans for low-grade infection in post-traumatic long bone non-unions. A mini-review was conducted using Pubmed in March 2024. A retrospective study was conducted including adult patients with a long bone non-union, suspected of infection. All patients underwent 18F-FDG PET-CT scans as the index test before surgical intervention, with peri‑operative cultures obtained during surgery serving as the reference standard. Quantitative analyses were performed on the standardized uptake value (SUV) measurements obtained from the 18F-FDG PET-CT scans. Diagnostic accuracy measures including sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated. Receiver operating characteristic (ROC) curve analysis was employed to evaluate the discriminatory ability of SUV measurements. Literature suggests that 18F-FDG PET-CT is the most accurate imaging technique to detect low-grade infections. The study included a total of 51 18F-FDG PET-CT scans and cultures from 50 patients with long bone non-unions. The diagnostic accuracy was found to be 0.67 (95 % CI 0.44-0.87). The PPV and NPV were calculated as 0.79 (95 % CI 0.53-1.00) and 0.52 (95 % CI 0.30-0.73), respectively. Quantitative analyses of SUV measurements demonstrated a low level of accuracy, with all area under the curve (AUC) values < 0.75 and ROC curves showing a trajectory fairly parallel to the diagonal line. The findings of this study indicate that in post-traumatic long bone non-unions, where a low-grade fracture-related infection (FRI) is suspected, the 18F-FDG PET-CT has a performance that is advantageous over other imaging techniques. A careful interpretation of the scan results is warranted, possibly including the quantitative analysis on tracer uptake as an adjunct. Nevertheless, the diagnostic accuracy in this condition is not as good as in early-onset FRI cases, and this should be taken into account when treating these challenging cases.