[Diagnosis of Periprosthetic Joint Infections]

Diagnosing periprosthetic joint infection (PJI) can be challenging, particularly in cases involving biofilm-forming organisms or low-virulence pathogens. Currently, no single test provides perfect sensitivity and specificity. However, distinguishing septic from aseptic complications is crucial for selecting an appropriate treatment strategy, reducing morbidity and mortality, and preserving joint function.The introduction of standardized infection definitions in 2011 has supported diagnostic accuracy and improved comparability between studies. Based on these PJI definitions, diagnosis relies on a combination of test methods, including clinical signs, serum parameters, joint aspiration, microbiological cultures (synovial fluid, tissue, sonication), histological analysis, and imaging.Preoperatively, the most accurate tests are the synovial leukocyte count and the percentage of polymorphonuclear neutrophils (%PMN). While synovial fluid culture may enable preoperative pathogen detection, its sensitivity is limited. Intraoperatively, 4-6 tissue samples should be collected for culture and histological evaluation. Tissue cultures are highly specific but may yield false-negative results in low-grade infections or in patients pre-treated with antibiotics. Histology (permanent sections), when performed with an optimal sampling technique, is one of the most reliable intra- and postoperative diagnostic modalities. Frozen sections allow for rapid intraoperative diagnosis. Sonication of removed implants is used to complement microbiological analysis. Additionally, molecular techniques such as next-generation sequencing (NGS) show promising results and may serve as useful adjuncts to conventional culture methods.