2. Department of Orthopedic Surgery, Mayo Clinic 200 First Street S.W., Rochester, MN 55905, USA.
Background: While patients with rheumatoid arthritis (RA) are known to be at an increased risk of periprosthetic joint infection (PJI), it remains unclear if the optimal threshold for the Musculoskeletal Infection Society (MSIS) minor criteria differs in patients with RA. The purpose of this study was to determine which of the MSIS minor criteria is best in patients with RA and to determine optimal thresholds for the MSIS minor criteria in this patient population.
Methods: A retrospective review of 842 patients from 2004 to 2016 was conducted and included 58 RA and 784 non-RA patients. The diagnosis of PJI was based on the revised MSIS criteria. Receiver operating characteristic (ROC) curves were used to evaluate erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and synovial fluid white blood cell (WBC) count and polymorphonuclear neutrophil percentage (PMN%) for diagnosing a PJI with Youden J statistics to determine optimal thresholds.
Results: In the RA group, the synovial fluid WBC count area under the curve (AUC) was 94% with a cutoff of 4600 cells/μL, while in the non-RA group, the AUC was 96% with an optimal cutoff of 3100 cells/ μL (p=0.49). The threshold value for synovial fluid PMN% was 80% with an AUC of 94% in RA patients and 87% with an AUC of 94% in non-RA patients (p=0.31). The threshold ESR value was 58 mm/hr with an AUC of 84% in RA patients and 52 mm/hr with an AUC of 85% in non-RA patients (p=0.83). The threshold value for CRP was 27 mg/L with an AUC of 77% in RA patients and 21 mg/L with an AUC of 86% in non-RA patients (p=0.31). However, none of the differences in threshold values were statistically significant.
Conclusion: While the MSIS minor criteria have standard defined thresholds for the diagnosis of a PJI, not all minor criteria are equivalent and the ideal thresholds for some of the minor criteria may vary based on underlying patient medical comorbidities. In this cohort, synovial fluid WBC count was the best diagnostic test for the diagnosis of a PJI in patients with RA.
Keywords: Total Joint Arthroplasty, Periprosthetic Joint Infection, Musculoskeletal Infection Society, Rheumatoid Arthritis