Joint effusion of the knee: potentialities and limitations of ultrasonography.

PURPOSE: This study aimed at comparing the diagnostic accuracy of ultrasonography (US) and magnetic resonance imaging (MRI) for the detection of joint effusion of the knee. METHODS: For this retrospective study, approbation by the institutional review board was not required, and written informed consent from the patients was waived. One hundred and fifty-eight patients (83 men and 75 women; median age 41.2 years; age range 13-81 years) who underwent US and MRI of the knee were included in the study. The sensitivity and specificity of US with respect to MRI in the evaluation of the effusion of the knee and in each recess were compared. RESULTS: In evaluating joint effusion of the knee, compared with MRI, US correctly identified 78 of 96 patients with joint effusion, showing a sensitivity of 81.3 % and a specificity of 100 %, with a positive predictive value (PPV) of 100 % and a negative predictive value (NPV) of 77.5 % (p value = 0.001). Various results were obtained comparing ultrasound with MRI, regarding the various recesses. CONCLUSION: US showed high specificity and sensitivity in diagnosing knee joint effusion and could be used in patients who cannot undergo MRI