Fluorodeoxyglucose positron emission tomography imaging for diagnosing periprosthetic hip infection: the importance of diagnostic criteria

Fluorodeoxyglucose positron emission tomography (FDG-PET) is a novel method of assessing suspected periprosthetic hip infection. However, a heterogeneity of sensitivity and specificity using different diagnostic criteria across clinical studies has been published. The objective of this study is to evaluate the various diagnostic criteria using FDG-PET in diagnosing periprosthetic hip infection. FDG-PET scans of patients suffering from painful hip prostheses between 2008 and 2015 were retrospectively reviewed. The PET images were considered positive for infection using five criteria: any increased uptake at the (1) bone-prosthesis-interface, (2) periprosthetic soft tissue (PST), or (3) both, (4) increased uptake in the bone-prosthesis-interface compared to the PST, and (5) increased uptake along the femoral bone-prosthesis-interface. The final diagnosis of infection was based on the pre-operative and intra-operative findings with clinical follow-up > 12 months. A total of 33 hip prostheses were evaluated in this study, of which 16 were determined to be infected and 17 uninfected. Any periprosthetic FDG uptake was found in all symptomatic prostheses (sensitivity 100%; specificity 0%). When increased uptake in the bone-prosthesis-interface (sensitivity 100%; specificity 65%) or PST (sensitivity 94%; specificity 59%) was considered infected, specificity increased. A higher intensity of uptake at the bone-prosthesis-interface than PST demonstrated only moderate specificity (sensitivity 44%; specificity 71%). The most specific criterion for infection was an increased FDG uptake along the femoral bone-prosthesis-interface (sensitivity 81%; specificity 94%). Our results demonstrated that the accuracy of FDG-PET is highly dependent of the diagnostic criteria used for periprosthetic hip infection. Only an acceptable diagnostic accuracy (sensitivity 81%; specificity 94%) was found when increased FDG uptake along the femoral bone-prosthesis-interface was considered positive for infection.