title: Joint effusion of the knee: potentialities and limitations of ultrasonography.
abstract: OBJECTIVE
  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.
  
  
  CONCLUSIONS
  US showed high specificity and sensitivity in diagnosing knee joint effusion and could be used in patients who cannot undergo MRI.
authors.affiliation: Institute of Radiology, University of Pavia, Viale Golgi 5, 27100 Pavia, Italy.
authors.forename: Ferdinando
authors.initials: F
authors.lastname: Draghi
authors.affiliation: Institute of Radiology, Second University of Naples, Naples, Italy.
authors.forename: Luigi
authors.initials: L
authors.lastname: Urciuoli
authors.affiliation: Institute of Radiology, University of Pavia, Viale Golgi 5, 27100 Pavia, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Alessandrino
authors.affiliation: Institute of Radiology, University of Pavia, Viale Golgi 5, 27100 Pavia, Italy.
authors.forename: Riccardo
authors.initials: R
authors.lastname: Corti
authors.affiliation: Biostatistics and Clinical Epidemiology Unit, IRCCS Policlinico San Matteo Foundation, Pavia, Italy.
authors.forename: Luigia
authors.initials: L
authors.lastname: Scudeller
authors.affiliation: Institute of Radiology, Second University of Naples, Naples, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Grassi
keywords: Knee; Knee effusion; Magnetic resonance imaging; Ultrasound