This retrospective study was performed after receiving approval from the institutional review board. The inclusion criterion was patients undergoing irrigation and debridement surgery for acute PJI after primary TKA between 2012 and 2019 in the two institutions. Four attending surgeons (ST, MW, MM, MN) performed approximately 3800 primary TKAs during the study period. All PJIs with acute onset were initially treated with irrigation and debridement surgery. All surgical site infections were validated according to the 2018 International Consensus Meeting on Musculoskeletal Infection . The clinical presentation of PJI was classified as early postoperative infection, acute hematogenous infection, or chronic infection according to Segawa et al. . The exclusion criteria were patients with chronic PJI and patients who experienced PJI after revision TKA.
During irrigation and debridement surgery, the modular polyethylene insert was routinely exchanged. We removed hematoma, fibrous membrane, devitalized soft tissue, and scrubbed the surface of the implant. The selection of antibiotics was left to the discretion of the attending surgeons.
This study focused on the implant retention rate after acute PJI. We reviewed all medical records of patients undergoing irrigation and debridement surgery for acute PJI and investigated retention of all knee prostheses other than tibial inserts without the use of suppressive antibiotics at the final follow-up. We also identified the antibiotics used as initial intravenous therapy, causative organism, age, sex, height, body weight, body mass index, Charlson comorbidity index, and the time interval from symptom onset of infection to irrigation and debridement surgery.
First, eligible patients were divided into those receiving beta-lactam antibiotics as initial intravenous empirical therapy (beta-lactam group) and those receiving antibiotics other than beta-lactams (non-beta-lactam group). We compared the success rate of implant retention after acute PJI between the two groups. In addition, other parameters were compared between the groups. Tests were two-sided, and the level of significance was set at p < 0.05.
Second, multivariate logistic regression analysis was used to control for confounding factors and to distinguish independent risk factors for the failure of implant retention after irrigation and debridement surgery. The beta-lactam antibiotic as initial intravenous empirical therapy was included as a risk factor in the model. In addition, we employed the following factors that were shown in previous studies to affect the success rate of implant retention: (1) whether the causative organism was resistant to antibiotics or not , (2) the Charlson comorbidity index , and (3) the time interval from onset of infection to irrigation and debridement surgery . Adjusted odds ratios and 95% confidence intervals are presented.
All analyses were performed using the R statistical package (version 3.4.1; R Foundation for Statistical Computing).