Absence of Signature Inflammatory Markers in Synovial Fluid for Total Knee Arthroplasties Revised for Arthrofibrosis

Introduction: Current diagnostic criteria for arthrofibrosis are limited. Since many patients will be aspirated during their clinical course, synovial fluid analysis may supplement current diagnostic criteria for arthrofibrosis. The goal of this study was to determine a unique synovial fluid and inflammatory marker profile for diagnosing arthrofibrosis. Hypothesis: Patients with arthrofibrosis following total knee arthroplasty will have a unique synovial fluid aspirate profile compared to control patients to aid in diagnosis. Materials and methods: Between 2013 and 2017, 32 patients (32 total knee arthroplasties [TKAs]) underwent revision TKAs for arthrofibrosis. Fourteen patients had pre-revision aspirations. They were 2:1 matched based on age, sex, body mass index (BMI), and year of revision to 28 patients who underwent aseptic revision TKAs for reasons other than arthrofibrosis (control group). Mean age at revision was 66 years, with 64% males. Results: In TKAs revised for arthrofibrosis, mean total cell count was 828 cells/uL. These aspirates contained a mean distribution of 46% macrophages (range, 4–76%), 31% lymphocytes (range, 11–68%), 21% neutrophils (range, 0–75%), 1% other cells (mainly synovial cells; range, 0–11%), and 1% eosinophils (range, 0–7%). There was no significant difference in mean total cell count (p = 0.8) or mean distribution of macrophages (p = 0.6), lymphocytes (p = 0.1), neutrophils (p = 0.2), eosinophils (p > 0.9), or serum inflammatory markers (p > 0.7) when compared to controls. All aspirations were culture negative for infection. Discussion: The profile of arthrofibrotic synovial fluid aspirates and serum inflammatory marker values were similar to patients revised for non-arthrofibrotic aseptic etiologies. This suggests synovial fluid and serum inflammatory markers in non-infected knees with arthrofibrosis should expect to have characteristics similar to synovial fluid and inflammatory marker profiles in other aseptic diagnoses. Level of evidence: III; Retrospective case-control study.