Effect of Metabolic Derangement and Inflammatory Conditions on Diagnostic Criteria for Septic Arthritis

Introduction & Aim Septic arthritis describes inflammation of the synovial capsule and represents a true orthopaedic emergency. There is no single diagnostic criteria for septic arthritis, although clinical presentation, in conjunction with synovial fluid analysis, is used to support the diagnosis. Traditional thresholds of synovial fluid analysis based on total nucleated cell counts (TNC) (>50,000 cells), polymorphonuclear (PMN) cell percentages (>90% PMN), and gram stain are commonly employed. However, there remains a paucity of information regarding how immune dysregulation of metabolic and/or inflammatory disorders affects the immune response in the synovial fluid, and subsequently, diagnostic criteria. The current study investigated whether immune dysregulation from metabolic and inflammatory conditions affect synovial characteristics. Methods Patients >18 years of age diagnosed with septic arthritis between 01/01/2014 - 12/31/2024 were reviewed retrospectively to determine sources of immune dysregulation present at the time of diagnosis. Baseline patient characteristics, synovial fluid values, serum markers, and immune system classification were collected. Immune status characterizations included: cancer treatment, organ transplant recipient, medication-induced immunodeficiency, primary immunodeficiency, HIV infection, systemic illness (end-stage renal disease, decompensated cirrhosis, poorly controlled diabetes), and inflammatory conditions (rheumatoid arthritis, systemic Lupus erythematosus, or inflammatory bowel disease). Planned preliminary comparisons were made between immune status groups using ANOVA with post-hoc correction if significance was found at p<0.05. Results 583 patients were returned in the initial search with 93 determined to have potential immune dysregulation: 62 chronic systemic disease (66.67%), 21 inflammatory conditions (22.58%), 4 undergoing active cancer treatment (4.30%), 2 primary immunodeficiency (2.15%), 1 organ transplant recipient (1.07%), 1 neutropenia (1.07%), 1 acquired immunodeficiency (1.07%), and 1 myelodysplastic syndrome (1.07%). Due to the small sample size in many of the groups, a student t-test was used to compare the chronic systemic disease and inflammatory condition patients only. Conclusion Patients with chronic systemic disease and inflammatory conditions demonstrated variability in synovial and serum inflammatory markers with no statistically significant differences suggesting diagnostic criteria between the two may not differ. It is important to note that total nucleated cell counts were above the traditional 50,000 cell threshold for septic arthritis. These findings do not support changes to diagnostic criteria depending on presence of systemic disease or inflammatory condition. Therefore, larger cohorts are needed to better define these findings.