Institutional Review Board approval was attained before the commencement of this study and then, this study was performed in a tertiary care orthopedic center. A longitudinally institutional PJI database was queried from 2015 to 2019 for all PJI patients who were managed with surgeries (including DAIR, one-stage revision, and two-staged arthroplasty) at a single tertiary care joint center.
All PJI patients within this database met the 2011 MSIS criteria and the inclusion criteria were as follows:
1) PJI patients diagnosed by the 2011 MSIS criteria
2) PJI patients managed with revisions at this tertiary joint center
3) patients with preoperative aspiration culture results from preoperative intra-articular aspiration within 90 days from revisions.
4) Only the latest aspiration culture results were included in this study if repeated joint aspirations were performed before revisions.
Patients were excluded if the only available preoperative aspiration culture was performed at the outside hospital.
The process of inclusion and exclusion was shown in figure 1.
Chart Review and Data Collection:
Following demographic variables of included patients were also scrutinized and collected: the age, gender, BMI, joint, ASA scores, and comorbidities. Moreover, the culture results of preoperative and intraoperative specimens and corresponding AST were also recorded.
In this tertiary joint center, preoperative joint aspiration cultures were performed routinely in these PJI patients according to our institutional standards and this process had been described in previous studies. All preoperative aspirations and the surgeries for PJI were done at the same treating institution, and the intraoperative aspiration before capsular incision was considered as the intraoperative aspiration for comparison to pre-op results. The process of preoperative aspiration culture and intraoperative synovial fluid culture were summarized in figure 2.
The obtained synovial fluid was injected into a BacT/ALERT FA FAN (fastidious antimicrobial neutralization) (BioM´erieux) bottle for anaerobic bacterial culture and a BacT/ALERT PF Pediatric FAN (BioM´erieux) bottle for aerobic bacterial and fungal culture. Each bottle was incubated for 2 weeks, and VITEK-MS (BioM´erieux) was used for microorganism identification if pathogens were detected.
If a microorganism was revealed in either an aerobic bottle or an anaerobic bottle, this pathogen was recorded as the preoperative aspiration culture results. Then, antibiotic sensitivity tests were performed by disk diffusion according to the laboratory standard protocols.
According to the institutional protocols for PJI, if the patient received antibiotics within 2 weeks before joint aspiration, the joint aspiration was delayed until the patient was away from antibiotics for 2 weeks. Besides, no antibiotics were administrated before obtaining specimens sent for cultures in the PJI management surgeries.
The definition of concordance and discordance was consistent with previous studies and the patients were divided into 2 categories: the concordant group, and the discordance group. The concordant group was defined if both preoperative aspiration and intraoperative synovial fluid cultures revealed the same bacteria species with identical antibiotic resistance profiles. Otherwise, discordant cultures were defined.
To calculate the SE, SP, PPV, and NPV of preoperative aspiration culture and compare the difference between preoperative aspiration culture and intraoperative synovial fluid culture, the result of intraoperative synovial fluid culture was considered as the “gold” standard).
If the discordant rate between preoperative aspiration culture results and the intraoperative synovial fluid cultures results were significantly (95%CIlower>0), the necessity of intraoperative synovial fluid cultures was defined.
The baseline characterizes of the patients are described as continuous data and dichotomous data. The continuous data were presented as means or medians. The T-test is adapted to compare these data if the normal distribution is achieved for continuous variables. Otherwise, the rand-sum test is utilized. Dichotomous data were presented as frequencies and percentages. Then, these data were compared by chi-squared test or Fisher exact test. Statistical significance was defined if P<0.05 and statistical analysis was performed on SPSS (IBM version: 22.0), Power BI (Microsoft version: 2019), and Excel (Microsoft version: 2018). Power analysis was performed on PASS 11.0.