Predictors of Repeat Washout in the Isolated Septic Knee

Despite urgent operative management of septic knee arthritis with irrigation and debridement and culture-specific antibiotic therapy, the incidence of additional washouts in knee septic arthritis has been noted to be between 11.4 and 40%. The purpose of this study was to analyze preoperative and postoperative variables associated with failure of primary washout in septic knees. A retrospective review was conducted at a Level I trauma center for all patients with septic arthritis who underwent open irrigation and debridement from 2010 to 2023. Patients were excluded if they were noted to have a knee arthroplasty or additional infection source aside from bacteremia. Demographic information, comorbidities, dates of operative washouts, vitals, and inflammatory markers were noted. Ninety-seven patients met inclusion and exclusion criteria. Forty-two required an additional washout. The average number of days between the primary and secondary washouts was 4.9 days. Decreased age (p = 0.03) and primary Staphylococcus aureus culture (p < 0.01) were found to be significantly associated with failure of the primary washout. Preoperative vitals, inflammatory markers, age, body mass index, intravenous drug use, diabetes, and smoking were not found to be predictors of repeat septic knee washouts. Additional subgroup analysis on bacteremic patients and on C-reactive protein (CRP) trends postoperative day 1 and 2 found no significant predictors of single or repeat septic knee washout. Younger age and presence of S. aureus in aspiration cultures were significantly associated with failure of primary washout. Trending CRP in the immediate postoperative period is not an accurate predictor of repeat septic knee washout.