Refining the Role of Routine Synovial Alpha-Defensin in Periprosthetic Joint Infection Following Total Knee Arthroplasty: An Analysis of Limitations.

Background: The utility of the synovial alpha-defensin test in diagnosing periprosthetic joint infections (PJIs) remains controversial. This study aimed to examine the diagnostic utility of this test.

Methods: A retrospective review was conducted to identify adults evaluated for PJI following total knee arthroplasty at a single institution. Patient demographics, laboratory results, and operative details were recorded. Using the 2018 Musculoskeletal Infection Society (MSIS) criteria, cases were categorized as definitive, inconclusive, or negative for PJI. The sensitivity, specificity, positive predictive value, and negative predictive value of each MSIS criterion was determined. The number of patients whose PJI diagnosis was contingent on alpha-defensin positivity was calculated.

Results: Overall, 172 total knee arthroplasty patients were included, who had an average age of 70.4 years (range, 39 to 95). Of the 21 patients who met major criteria, 20 (95.2%) were alpha-defensin positive. Of the remaining 151 patients, 85 did not meet minor criteria, all of whom were alpha-defensin negative. Among the 30 patients who met minor criteria, 28 (93.3%) were alpha-defensin positive and 2 (6.7%) were negative. The remaining 36 patients were deemed inconclusive preoperatively. In total, alpha-defensin testing changed the diagnosis in only 9 of 172 patients (5.2%). The sensitivity, specificity, positive predictive value, and negative predictive value of alpha-defensin in this cohort were 94.1, 100, 100, and 97.6, respectively.

Conclusion: Alpha-defensin may assist in the diagnosis of PJI when a preoperative workup is inconclusive. However, this test is often unnecessary when the diagnosis of PJI can be made using the 2018 MSIS criteria.