Draining Sinus Tracts and Periprosthetic Joint Infections: Traditional Synovial Fluid Counts May Be Misleading

Serologic and synovial laboratory values guiding the diagnosis of periprosthetic joint infection (PJI) are well-established. We hypothesized that these values would be lower in patients who had a draining sinus tract. The purpose of this study was to determine if patients who had sinus tracts had lower values for serum erythrocyte sedimentation rate (ESR), serum C-reactive protein (CRP), synovial white blood cell (WBC) count, and synovial percent neutrophils.

We retrospectively reviewed 611 primary total joint arthroplasties treated for PJI between 2000 and 2020 at a high-volume academic center. Only 191 patients (94 hips, 97 knees) who met the 2011 Musculoskeletal Infection Society (MSIS) major criteria for PJI and did not receive antibiotics within two weeks before laboratory evaluation were included. Patients were divided into those who had sinus tracts (n = 58) and those who did not (n = 133). Laboratory values for early (less than 90 days) and late (≥ 90 days) postoperative PJI cases were analyzed separately. False negative rates for detecting PJI were compared based on the 2018 International Consensus Meeting (ICM) cutoffs for each diagnostic test.

Median synovial WBC count was significantly lower in early (9,978 versus 76,068 cells/μL; P = 0.01) and late (20,365 versus 63,356 cells/μL; P = 0.03) PJI in those who had a sinus tract. False negative rates for detecting PJI were significantly higher in patients who had a sinus tract compared to those who did not for synovial WBC (38 versus 6%; P = 0.02) and serum CRP (48 versus 15%; P < 0.0001).

Those who had a sinus tract had an approximately six times higher false negative rate for detecting PJI by synovial WBC. The false negative rate for detecting PJI by serum CRP was approximately three times higher in those who had a sinus tract. The presence of a sinus tract is diagnostic of PJI, and relatively lower laboratory values on workup should not lead clinicians to question this diagnosis.

Level IV - retrospective review.