Ultrasound abnormalities in septic arthritis are associated with functional outcomes

Abstract Objectives To describe the ultrasound abnormalities seen in septic arthritis and to assess their associations with clinical, biological, and radiological outcomes. Methods We prospectively included 34 patients with septic arthritis of a native joint (knee, n = 19; shoulder, n = 6; hip, n = 4; ankle, n = 3; or wrist, n = 2). Ultrasonography was performed to record synovial-membrane thickness and vascularity, joint effusion, and abnormalities of adjacent soft tissues, at baseline then 4 days, 2 weeks, and 3 months later. Motion-range limitation of the affected joint was evaluated after 3 months. Radiography was performed at inclusion and after 3 months. Results Mean age was 63.7 ± 17.6 years. After 3 months, 20 (58.8%) patients had motion-range limitation with worsening of the total radiological score ( P < 0.001). The proportion of patients with synovitis was very high initially (96.4% at baseline, 96.3% after 4 days, and 100% after 2 weeks) then diminished to 77.8% after 3 months ( P = 0.051). Synovial-membrane thickness was significantly higher after 4 days and 2 weeks compared to baseline (median, +17.3% and +20%, respectively; P = 0.015) and was significantly lower after 3 months compared to the earlier time points (median, −31.5%, P = 0.015). A positive Doppler signal was common at baseline ( n = 18, 64.3%) then significantly less so after 3 months ( n = 7, 25.9%; P = 0.04). An unchanged or higher Doppler grade after 2 weeks compared to baseline was associated with motion-range limitation at last follow-up ( P = 0.033). Conclusion We report the first study on ultrasound evidence of synovitis, joint effusion, and soft tissue alterations at baseline and over time in patients with septic arthritis. Persistent synovitis and joint effusion 3 months after starting antibiotic therapy was not associated with treatment failure. However, Doppler signal changes over the first 2 weeks were associated with the 3-month functional outcome.