SONICATION IS ESSENTIAL FOR DIAGNOSING FRACTURE-RELATED INFECTION (FRI)

Aim Fracture related infection (FRI) is a serious complication after fracture fixation. Identifying the causative pathogen is crucial for diagnosis and treatment. Sonication may be a valuable adjunct tool for diagnosing FRI. This study aims to evaluate the clinical benefit of adding sonication as a diagnostic tool. Methods We prospectively collected data of patients requiring removal of hardware after previous osteosynthesis in a large university hospital between 2012 and 2021. Based on preoperative findings, we categorized patients into three groups using AO Foundation and EBJIS FRI consensus criteria: presumed aseptic, suspected FRI, or confirmed FRI. Sensitivity and specificity of tissue and sonication fluid cultures were calculated. Microbiological cultures were analyzed to assess the impact on FRI diagnosis. The added value of sonication was determined as the percentage of cases where sonication was essential for diagnosing FRI. Results We included 337 patients. Based on preoperative findings alone we found: 61 presumed aseptic, 160 presumed suggestive FRI, and 116 confirmed FRI cases. After analyzing microbiology results, 2 presumed aseptic, 28 presumed suggestive, and all 116 confirmed were determined as FRI (146 FRI cases). The individual sensitivity of tissue and sonication fluid cultures were both 83%. The difference in individual specificity between tissue and sonication fluid cultures was not significant (71% vs. 73%, respectively). Combining tissue with sonication fluid cultures significantly increased sensitivity and specificity to 92% and 87%, respectively (p <0.001). Sonication was essential for FRI diagnosis in 65 cases (45%), including 13 delayed FRI, and 52 late FRI. Sonication was less relevant in FRI cases with 3 or more tissue cultures compared to cases with 1 or 2 tissue cultures (30% vs. 61%, p < 0.001). Sonication was required for microbiological diagnosis in 10 of 33 FRI cases with preoperative administration of antibiotics (27%). In polymicrobial cases, sonication detected additional pathogens in 12 out of 53 polymicrobial FRI cases (23%). Conclusions Sonication significantly improves sensitivity and specificity of FRI diagnostics. Without sonication, 65 FRI cases would have been misdiagnosed or were at risk for inadequate treatment. Sonication is essential in both delayed and late FRI, as well as patients who preoperatively received antibiotics. In every patient suspected for FRI, at least 3 deep tissue cultures should be obtained, and additionally sonication should be performed.