Histopathology is More Reliable Than Microbiology for Detecting Residual Osteomyelitis After Conservative Surgery for Diabetic Foot: The Pitfall of False-Positive Cultures and the Role of Pseudomonas aeruginosa.

The optimal method for assessing residual osteomyelitis after conservative surgery for diabetic foot infection remains controversial. Microbiological cultures are frequently used due to their rapid turnaround and utility in guiding antibiotic therapy, but their diagnostic reliability is uncertain. This study compared microbiological cultures and histopathology in evaluating bone resection margins, using histopathology as the gold standard. We included 93 patients undergoing conservative surgery for diabetic foot osteomyelitis. Bone samples were obtained from the proximal resection margin for both microbiology and histopathology. A microbiological result was considered contamination when cultures were positive but histopathology was negative. Microbiological cultures at bone resection margins yielded 52 true positives, 23 false positives (contamination), 10 false negatives, and 8 true negatives when compared to histopathology. This resulted in a sensitivity of 83.9%, specificity of 25.8%, positive predictive value of 69.3%, and negative predictive value of 44.4%. Contamination was not associated with the severity of infection, presence of soft tissue involvement, inflammatory markers, or glycemic control. No association was found between contamination and polymicrobial flora in the primary surgical specimen. However, Pseudomonas aeruginosa was the only species significantly associated with contamination (p = .008), suggesting species-specific factors may contribute to microbiological false positives. These findings emphasize that microbiology, while sensitive, is not a specific method for assessing residual bone infection and should not be used in isolation. Histopathology remains the more reliable diagnostic tool. Future research should explore biofilm-targeted strategies and intraoperative antiseptic protocols to reduce contamination of bone biopsy specimens obtained from resection margins.