Diagnosis of joint effusion on lateral and axial projections of the knee.

Lateral and axial scout radiographs of 100 patients undergoing knee arthrography were evaluated for the presence of joint effusion by multiple observers. Specific observations were characterized. Knee joint effusions were diagnosed with comparable overall accuracy on lateral and axial projections. The combination of both projections increased sensitivity from 75% to 91% and decreased specificity from 87% to 27%.