Impact of removed prostheses sonication on prosthetic joint infections diagnosis and outcome

Background: Sonication of removed implant may improve the rate of microbiologic diagnosis of prosthetic joint infections (PJI) but the value of a sonication-guided therapy is unknown. Objectives: To evaluate the impact of sonication in ameliorating quality of microbiological diagnosis and consequently in improving cure rate of PJI. Methods: PJI undergoing two-stage exchange consecutively observed during a 4-year period were enrolled. PJI were defined by clinical, microbiological and radiologic findings. In each case, we reported demographic, clinical and microbiological data, including the method employed to obtain microbiological cultures such as conventional culture of intraoperative specimens or culture of the fluid obtained by sonication of the removed implant. Cure was defined by disappearance of any evidence of infection during a 6-month follow-up period. Results: Thirty-seven cases with PJI were observed (median age 64 [range 48–82], 16 hip implants and 21 knee implants). Microbiological investigations revealed bacterial growth in 30 (81%). Staphylococcus aureus was identified in 12 (40%) cases (eight methicillin resistant), Coagulase Negative staphylococci (CoNS) were identified in 10 (33%), Pseudomonas aeruginosa in 3 (10%), and other bacteria in 5 (17%). In 15 PJI the attempt to microbiological diagnosis was made only by conventional methods reporting a 67% success rate. In 22 cases undergoing both culture of the fluid obtained by sonication and culture of conventional intraoperative specimens, bacterial growth was obtained in 20 (90%) by sonication and 15 (68%) by conventional methods. Three cases reported discordant microbiological evidences between sonication and conventional methods and received antimicrobial therapy according to sonication. Overall, cultures were positive in 90% by sonication and 68% by conventional methods (20/22 vs. 25/37; RR 1.35, 95% CI 1.04–1.74; p = 0.04) with an increase of CoNS isolated among those diagnosed by sonication. Failure after twostage replacement was reported in 3 (20%) diagnosed by conventional methods and 1 (5%) diagnosed by sonication. Conclusion: Sonication of the implant improved the accuracy of PJI microbiological diagnosis revealing a higher number of cases sustained by CoNS which are better revealed by sonication since are embedded within biofilm. Sonication resulted in slight better cure rate, probably because of the reduction of cases needing broad spectrum empiric therapy.