Tapping our resources: do preoperative aspirations add diagnostic value in hip and knee periprosthetic joint...

Background: Discrepancies exist between preoperative synovial aspirations and intraoperative cultures. It is unclear whether the results of preoperative arthrocentesis add diagnostic value for patients with possible prosthetic joint infection (PJI). Methods: We retrospectively identified adult patients treated surgically for hip and knee PJI who underwent both preoperative aspiration and intraoperative sampling. Synovial and intraoperative culture results were analyzed. Cultures were defined as concordant if they yielded the same organism(s) or if both were negative. Cultures were considered to be discordant if different organisms were isolated or if one had growth and the other was sterile. Demographic, clinical, and laboratory variables between groups were compared. Results: Among 75 patients, 54 (72 %) had concordant results, and 21 (28 %) had discordant results. In the discordant group, 7 of 21 patients (33 %) had negative synovial cultures with positive intraoperative cultures. Among culture-positive concordant patients, staphylococci and streptococci were the most common isolates, with 20 % gram negatives. True culture-negative PJI was uncommon ( $n=1$ ). Preoperative antibiotic exposure was frequent ( $>50$ %) in both groups. Conclusion: In a cohort of hip and knee PJI patients treated surgically, preoperative synovial aspiration cultures were concordant with intraoperative cultures in 72 % of cases, but negative synovial aspirations did not reliably exclude infection. Given the observed discordance, our findings support the obtainment of preoperative synovial aspiration and the collection of multiple intraoperative specimens at the time of surgery.