Detection of Knee Effusion by Ultrasonography

Objectives: The purpose of this study was to assess which scan view was sensitive in detecting knee effusion by ultrasonography while infusing normal saline in cadaveric specimens. Design: Intraarticular injection of normal saline with contrast dye was done in increments (5, 10, 15, and 20 ml) into the knee joint of eight fresh cadavers. After infusion of each amount, sonographic images were obtained with five different scans: medial, midline, and lateral on longitudinal scans, and medial and lateral on transverse scans. When 20 ml had been injected, the knee was flexed at 30 degrees and serial images were taken. Results: After infusion of 10 ml, effusion of more than 2 mm depth with ultrasonography was most frequently seen in lateral transverse scans (14/14), and the next most frequent view was a lateral longitudinal scan (11/14). After knee flexion, the amount of effusion was increased on medial and middle longitudinal scans and was decreased on transverse scans. Conclusions: For detecting knee effusion by ultrasonography, lateral transverse and longitudinal scans were the most sensitive in the knee extension posture. With knee flexion at 30 degrees, effusion was more readily detected on the medial and midline longitudinal scans than with knee extension.