Diagnostic Accuracy of Physical Examination of the Knee in Rheumatoid Arthritis: Clinical and Ultrasonographic Study of Joint Effusion and Baker's Cyst

Abstract

In patients with rheumatoid arthritis (RA), knee pain can be inflammatory, mechanical or extraarticular. The physical examination (PE) doesn't always detect the presence of knee joint effusion or Baker's cyst (BC) in the knees of these patients.To determine the diagnostic accuracy of PE in the diagnosis of effusion and BC in patients with RA evaluated with musculoskeletal ultrasound (MSUS), using this technique as the gold standard for comparison.Three different models of ultrasound machines with a 7.5 MHz linear probe were used (Toshiba Tosbee, Toshiba Capasee and Siemens Sonoline). A rheumatologist evaluated the presence or absence of knee joint effusion or BC in patients. We registered age, gender, time of evolution of RA, rheumatoid factor, treatment, functional class of RA (FCRA) and previous clinical diagnosis to the MSUS study.40 patients (80 knees) with RA were evaluated. Eighty percent were women, mean age 61.3±15 years. Time since onset of RA was 9.5±11.3 years, rheumatoid factor was positive in 80%, FCRA I (3 patients), FCRA II (27), FCRA III (8), FCRA IV (2). Fifty five percent of the patients received methotrexate. Patients reffered pain in 26 knees (32.5%). Joint effusion was reported by the clinician in 35 knees (43.7%) and corroborated by MSUS in 31 knees (38.75%), BC was reported by the clinician in 12 knees (15%) and corroborated by MSUS in 6 knees (7.5%). The sensitivity of the PE for detection of joint effusion was 0.63 and specificity of 0.87, for the detection of BC was 0.43 and 0.91, respectively.The PE showed acceptable diagnostic accuracy for the clinician. The complementary use of the MSUS can change the therapeutic and diagnostic approach in patients with RA.