Alpha-defensin lateral flow test does not appear to be useful in predicting shoulder periprosthetic joint infections.

Periprosthetic joint infections (PJIs) remain a challenging complication after shoulder arthroplasty. The antimicrobial peptide α-defensin has been proposed as a new synovial fluid biomarker in diagnosing PJIs. To date, only little data are available on the diagnostic accuracy of α-defensin in shoulder PJIs; thus, we aimed to evaluate its diagnostic value in a cohort of patients with a suspected shoulder PJI. Between June 2016 and June 2018, we prospectively enrolled patients with a diagnostic shoulder aspiration due to painful shoulder arthroplasty or planned revision surgery. PJI diagnostics were performed according to the Musculoskeletal Infection Society (MSIS) criteria. All patients with an antibiotic therapy within two  weeks before enrollment, insufficient amount of synovial aspirate, or bloody aspiration were excluded. α-Defensin was measured in the synovial fluid using the α-defensin lateral flow (ADLF) test (Synovasure®). Out of 60 patients, we could include 29 (59% female) patients with a mean age of 70 (range, 50-92) years. A shoulder PJI was detected in five cases (Staphylococcus aureus, n = 2; Staphylococcus epidermidis, n = 2; Cutibacterium acnes, n = 1). The ADLF test was positive in seven out of 29 cases. According to the MSIS criteria, the ADLF test was false-negative in two patients and false-positive in four patients, resulting in sensitivity, specificity, and positive and negative predictive value of 60%, 83%, 43%, and 91%, respectively. The overall accuracy was 79%. The ALDF test does not appear to be useful in predicting shoulder PJIs but may be used as an additional diagnostic factor in rejecting these infections.