Fig. 1

Representative images of the suprapatellar effusion area. a Ultrasound scan image of the suprapatellar effusion acquired by placing a linear probe longitudinally on the suprapatellar pouch. The effusion area was calculated by tracing the margin of the echo-free space that corresponds with the suprapatellar pouch. During the examination, the transducers should be placed on the subject as gently as possible to avoid distorting the acquired area. Representative images of the suprapatellar effusion area: 30 mm² (b); 50 mm² (c); and 100 mm² (d)