Improvement in the Detection Rate of PJI in Total Hip Arthroplasty Through Multiple Sonicate Fluid Cultures

Introduction Sonicate fluid cultures (SFC) are more sensitive than conventional microbiological methods in identifying periprosthetic joint infections (PJI), because sonication enables a sampling of the causative bacteria directly from the surface of the endoprosthetic components. Because of their high sensitivity SFC can be positive while all other microbiological methods remain negative. It is therefore difficult to interpret a single SFC as being truly or falsely positive. The aim of this prospective study was to improve the interpretation of SFC in the diagnosis of PJI in patients after total hip arthroplasty through the use of multiple SFC. Material and methods 102 patients of which 37 had a defined PJI according to the following criteria were included: intraarticular pus or a sinus tract, a periprosthetic membrane (PM) indicative of infection, or a positive microbiological culture in a minimum of 2 separate microbiological samples. A single positive microbiological sample was classified as false positive. In 35 patients multiple SFC were acquired from the separate endoprosthetic components. Results Out of all individual diagnostic parameters SFC achieved the highest sensitivity with 89% and a specificity of 72%. PM was able to achieve a sensitivity of 78% for the detection of PJI. Out of the 35 patients with multiple SFC it was possible to newly diagnose a PJI in 3 cases solely through multiple isolations of the same bacterial species in SFC. In the same group it was also possible to exclude the suspicion of PJI in 3 cases, because only one of the multiple samples presented a bacterial isolation, while the other samples remained negative. When multiple SFC were employed it was possible to increase the sensitivity to 100% and the specificity to 85%. Conclusion In our study SFC were the most sensitive diagnostic parameter for detection of PJI and our results show that it is possible to further increase the sensitivity and specificity of SFC when multiple samples are used. The acquisition of multiple SFC facilitate the diagnosis of PJI, since they are able to present the 2 positive bacterial isolations that are needed for making the diagnosis of PJI. Multiple SFC can help to solve the orthopaedic surgeon9s diagnostic dilemma of having to interpret a single positive bacterial isolation by confirming the bacterial isolation in a second SFC sample.