Ultrasonography is superior to clinical examination in the detection and localization of knee joint effusion in rheumatoid arthritis.

Objective: Musculoskeletal ultrasonography allows real-time imaging of joint structures and may be used to complement clinical examination in rheumatological practice. We compared ultrasonography (US) with clinical examination (CE) in the detection of effusion, suprapatellar bursitis, and Baker's cyst of the knee in rheumatoid arthritis (RA) in order to determine whether US provided additional clinical information.

Methods: A total of 22 patients with RA (ACR criteria) underwent independent clinical and US examination of both knees for suprapatellar bursitis, knee effusion, and presence of Baker's cyst. US was performed using an ATL HDI 3000 machine with L7-4 MHz and CL10-5 MHz probes. Clinical examination was performed using standard techniques by an experienced rheumatologist. Patients with previous knee surgery were excluded from the study.

Results: A total of 44 knees were examined at a total of 130 sites (one patient was unable to lie prone for US of popliteal fossae). US detected soft tissue abnormality (suprapatellar bursitis, knee effusion, or Baker's cyst) at 54/130 (42%) sites, while CE detected soft tissue abnormality at 36/130 (28%) sites. US detected 17 (39%) cases of suprapatellar bursitis in 44 knees, 7 (16%) of which were detected on CE. US detected 27 (61%) knee joint effusions in 44 knees, 16 (36.36%) of which were detected on CE. US detected 10 (23.81%) Baker's cysts in 42 knees, 2 (4.76%) of which were detected on CE. Taking US of the knee as the gold standard, CE was specific but not sensitive in the detection of soft tissue abnormality of the knee in RA.

Conclusion: US is more sensitive than CE in the detection of suprapatellar bursitis, knee effusion, and Baker's cyst in RA. CE underestimates knee inflammation in RA. This has implications for the use of CE as a component of standardized disease activity scores and in guiding knee joint aspiration.