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

Diagnosis of periprosthetic joint infection (PJI) in patients with inflammatory arthritis (IA) is challenging, as features of IA flares can mimic infection. We aimed to cross-sectionally determine if the optimal tests to diagnose PJI in osteoarthritis were present in patients with IA flares.

We enrolled patients from October 2020 to July 2022 in 3 groups: ( a ) PJI-total joint arthroplasty patients undergoing revision for infection, ( b ) IA Flare-IA patients with a flaring native joint, and ( c ) IA Aseptic-total joint arthroplasty patients with IA undergoing aseptic arthroplasty revision. We compared blood and synovial fluid markers between the cohorts using Kruskal-Wallis and Fisher exact tests to assess marker sensitivity and specificity.

Of 52 cases overall, 40% had rheumatoid arthritis, 20% psoriatic arthritis, and 11% osteoarthritis (in PJI group). PJI cases had higher C-reactive protein (CRP) and synovial fluid polymorphonuclear neutrophil percentage (%PMN). Alpha-defensin tested positive in 93% of PJI cases, 20% of IA Flares, and 6% of IA Aseptic ( p < 0.01). Synovial white blood cell count >3000/μL and positive alpha-defensin were highly sensitive (100%) in diagnosing infection; however, specificity was 50% for white blood cell counts and 79% for alpha-defensin. PJI diagnosis was nearly 5 times more likely with positive alpha-defensin and almost 6 times more likely with %PMNs >80. Blood markers interleukin-6, procalcitonin, and d -dimer were neither sensitive nor specific, whereas erythrocyte sedimentation rate and CRP showed 80% sensitivity, but 47% and 58% respective specificities.

Although synovial %PMNs, CRP, and alpha-defensin are sensitive tests for diagnosing PJI, they are less specific and may be positive in IA flares.