What is the Clinical Utility of Synovial Alpha Defensin Testing of Antibiotic Spacers Before Reimplantation

Abstract Introduction The purpose of this study was to evaluate the diagnostic performance of standalone alpha-defensin (AD) testing of antibiotic spacers during two stage exchange, and to determine if the addition of AD testing to other commonly utilized laboratory tests improves the ability to detect persistent infection in an antibiotic spacer. Methods Cases of two-stage exchange for periprosthetic joint infection (PJI) from 2016-2019 at a single institution were retrospectively reviewed. Cases were classified as persistently infected or not infected according to 2014 and 2018 Musculoskeletal Infection Society (MSIS) criteria to determine if AD provided any clinical utility beyond the other commonly utilized tests that make up both criteria. Delphi Consensus criteria at 1 year were used as the gold standard for determining recurrent PJI. Results Fifty-two spacers (25 hips, 27 knees) in 51 patients were included for analysis. Five spacers were persistently infected based on MSIS criteria. One spacer underwent re-resection and the remaining 4 underwent reimplantation with no subsequent infectious complications. All 48 patients that were categorized as not infected underwent reimplantation; at 1 year postoperatively, 7 (13%) had failed due to infection. Three spacers (6%) had a positive AD test. Two spacers with positive AD tests underwent reimplantation; neither had failed at 1 year postoperatively. Sensitivity of standalone AD testing was 0% and specificity was 96%. Conclusion Standalone AD testing for the purpose of predicting repeat infection following two-stage exchange arthroplasty exhibits sensitivity of 0% and low predictive value. Addition of synovial AD testing did not increase the diagnostic performance of commonly utilized synovial and serologic markers of infection.