Abstract
<title>Abstract</title> <p> Background The microbiological characteristics, surgical procedures, and treatment outcomes of knee infections may differ substantially. This investigation focused on assessing the microbial profiles, treatment approaches, and rates of infection-free survival in cases of periprosthetic joint infections (PJI) following total knee arthroplasty (TKA), unicompartmental knee arthroplasty (UKA), and native knee septic arthritis (NKSA). While TKA‑PJI and NKSA are relatively well studied, the microbiological and treatment profiles of UKA‑PJI remain poorly defined. Methods We retrospectively reviewed patients treated for knee infections at two institutions between May 2015 and May 2025. The study included 33 cases of TKA-PJIs, 13 cases of UKA-PJIs, and 33 instances of NKSA. The analysis focused on demographic information, the microorganisms involved, surgical interventions, and the infection-free survival rates at the last follow-up. Results Notable differences were observed in microbial profiles among the three groups. <italic>Coagulase-negative staphylococci</italic> (CoNS) were most prevalent in the UKA-PJI group (38.5%). Furthermore, the occurrence of CoNS was considerably higher in the UKA-PJI group when compared to the TKA-PJI group (OR = 6.25; 95% CI: 1.24–31.45; <italic>P</italic> = 0.027), while Gram-negative bacilli were more frequent in the NKSA group (21.2%). Culture-negative rate was highest in the TKA-PJI group(36.4%). Nonetheless, <italic>Staphylococcus aureus</italic> (including MRSA) was frequently identified in all categories. Two-stage reconstruction was performed in 84.8% of TKA-PJI cases but only in 46.2% of UKA-PJI cases, while debridement, antibiotics, and implant retention (DAIR) was utilized more often in the UKA-PJI group. DAIR success was higher in UKA-PJI (80.0%) than in TKA-PJI (60.0%). After an average follow-up period of 47.4 months, the infection-free survival rates were recorded as 84.8% for TKA-PJI, 92.3% for UKA-PJI, and 93.9% for NKSA. Conclusion In our cohort, UKA-PJI was associated with a predominance of CoNS, a relatively high DAIR success rate, and effective overall infection control;TKA-PJI exhibits a significant rate of culture negativity, typically managed with a two-stage revision procedure; NKSA is primarily associated with acute infections from <italic>Staphylococcus aureus</italic> ; therefore, immediate debridement should be considered, with subsequent two-stage reconstruction possible after eradication of infection. Our findings support an implant-specific treatment algorithm, with DAIR as a viable option for selected acute UKA-PJI cases, while two-stage revision remains the mainstay for TKA-PJI and chronic infections. Limitations include the retrospective design and the small UKA‑PJI cohort, which warrant cautious interpretation. </p>