Typical histological section after 3-months period. (Alcian blue stain x 100). (A) The Sham group: Intact osteochondral architecture was shown. The surface of cartilage layer is smooth and the arrangement of chondrocyte is well. (B) The without-LIPUS-treatment group: The cartilage layer was thin because of lack of superficial zone, intermediate zone and radial zone of cartilage layer. Irregular surface without proliferative layer was shown (arrow). (C) The with-LIPUS-treatment group: The layers of superficial zone, intermediate zone and radial zone were lost over the cartilage defect, instead of deposition of acellular tissue layer (arrow). SZ: superficial zone; IZ: intermediate zone; RZ: radial zone; CZ: calcification zone; SB: subchondral bone.