Periprosthetic Joint Infection in Patients With Inflammatory Arthritis: Optimal Tests to Differentiate From Flares

Area of Science:

• Orthopedics
• Rheumatology
• Infectious Diseases

Background:

• Diagnosing periprosthetic joint infection (PJI) in patients with inflammatory arthritis (IA) presents a challenge due to overlapping symptoms between IA flares and infection.
• Existing diagnostic criteria for PJI in osteoarthritis may not be directly applicable to patients with IA.

Purpose of the Study:

• To evaluate the utility of established periprosthetic joint infection diagnostic markers in patients experiencing inflammatory arthritis flares.
• To determine if optimal tests for diagnosing PJI in osteoarthritis are effective in patients with IA flares.

Main Methods:

• A cross-sectional study enrolled 52 patients from October 2020 to July 2022 into three groups: PJI revision, IA flare, and IA aseptic revision.
• Blood and synovial fluid markers were compared between cohorts using Kruskal-Wallis and Fisher exact tests to assess sensitivity and specificity.
• Key markers analyzed included C-reactive protein (CRP), synovial fluid polymorphonuclear neutrophil percentage (%PMN), and alpha-defensin.

Main Results:

• Periprosthetic joint infection cases exhibited elevated CRP and synovial fluid %PMN.
• Alpha-defensin tested positive in 93% of PJI cases, significantly higher than in IA flare (20%) or IA aseptic (6%) groups (p < 0.01).
• Synovial white blood cell count >3000/μL and positive alpha-defensin demonstrated 100% sensitivity for infection but had lower specificities (50% and 79%, respectively).

Conclusions:

• Synovial %PMN, CRP, and alpha-defensin are sensitive indicators for diagnosing PJI.
• However, these markers lack sufficient specificity and can yield positive results during inflammatory arthritis flares, complicating diagnosis.
• Further refinement of diagnostic strategies is needed for PJI in the context of inflammatory arthritis.