Sonication fluid cultures enhance pathogen identification in fracture-related-infection (FRI)

Background: Sonication fluid culture (SFC) of osteosynthesis material may be a valuable adjunct tool to diagnose fracture-related infection (FRI). This study aims to evaluate the added diagnostic value of SFC as a diagnostic tool. The diagnostic value of SFC was assessed by evaluating its impact on confirming microbiological results and changing diagnosis. Methods: We analysed patients undergoing osteosynthesis hardware removal between 2012 and 2021. We categorized patients using FRI consensus criteria: suspected FRI or confirmed FRI. The sensitivity and specificity of tissue cultures and SFC were assessed. The added value of SFC was determined as the number of cases where SFC was essential for confirming FRI and the influence on antibiotic therapy selection. Results: We included 96 patients with three or more tissue cultures. Based on diagnosis without SFC, we found 14 aseptic, 35 suggestive FRI cases, and 47 confirmed FRI cases. Following SFC results, four cases changed diagnosis from aseptic to suggestive FRI, and three cases changed from suggestive FRI to confirmed FRI. The sensitivity of tissue culture was 74 %, and the specificity was 98 %. The sensitivity of SFC was 84 %, and the specificity was 83 %. Combining tissue cultures with SFC significantly increased sensitivity compared with tissue cultures alone, from 74 % to 88 % ( $p<0.001$ ). In 21 confirmed FRIs (42 %), SFC results were concordant with tissue cultures and would not alter FRI management. SFC detected an additional virulent pathogen in three confirmed FRIs (6 %) and low-virulent pathogens in eight confirmed FRIs (16 %) which could influence the antibiotic regimen. Conclusions: SFC plays a significant role in diagnosing FRI by enhancing pathogen detection. SFC may influence FRI management in approximately 6 % to 16 % of confirmed FRI. In every FRI, an adequate number of cultures according to protocol should be obtained, and SFC should also be performed.