α-Defensin as a predictor of periprosthetic shoulder infection

Background: Diagnosis of periprosthetic joint infection (PJI) in revision shoulder arthroplasty can be challenging because of the indolent nature of the common offending organisms. The purpose of this study was to evaluate the diagnostic utility of synovial fluid a-defensin levels in identifying PJI of the shoulder. Methods: Thirty patients evaluated for painful shoulder arthroplasty were prospectively enrolled and underwent revision surgery (n = 33 cases). Cases were categorized into infection (n = 11) and no-infection (n = 22) groups on the basis of preoperative and intraoperative findings. Synovial fluid was obtained from preoperative aspirations or intraoperative aspiration before arthrotomy. a-Defensin was tested by the Synovasure (CD Diagnostics, Wynnewood, PA, USA) test for joint infection. Synovial fluid was also obtained intraoperatively from a control group undergoing arthroscopic rotator cuff repair (n = 16) for baseline data on normal a-defensin levels in the shoulder. Areceiver operating characteristic curve was used to determine the diagnostic utility of synovial fluid a-defensin. Results: Synovial a-defensin had an area under the curve, sensitivity, specificity, and positive and negative likelihood ratios of 0.78, 63%, 95%, 12.1, and 0.38, respectively. There was a significant difference in a-defensin levels between the infection (median, 3.2 S/CO [signal to cutoff ratio]) and no-infection groups (median, 0.21 S/CO; P =.006). Synovial a-defensin was elevated in the presence of a culture positive for Propionibacterium acnes (median, 1.33 S/CO; P =.03) and showed moderate correlation with the number of positive cultures. Conclusion: Synovial fluid a-defensin was more effective than current diagnostic testing in predicting positive cultures and may be an effective adjunct in the workup of shoulder PJI. Level of evidence: Level III, Diagnostic Study. (C) 2015 Journal of Shoulder and Elbow Surgery Board of Trustees.