Sagittal view proton density fast spin echo sequence MR images (TR/TE 4000/30) of operated knee in the with-LIPUS-treatment group. Subchondral bone demonstrated lower signal intensity, while articular cartilage showed intermediate signal intensity and joint fluid showed high signal intensity. (A) Pre-surgery: Intact articular surface of femoral condyle (arrow), and a boundary between joint fluid and articular cartilage were seen. (B) Post-surgery: Cartilage defect showed loss of continued articular surface over femoral condyle (arrow). (C) Post-LIPUS treatment: Proliferative tissue filled the cartilage defect of femoral condyle (arrow). A boundary between joint fluid and proliferative tissue was seen, which presented intermediate signal intensity.