Intraoperation of repaired articular cartilage and low-power-field microscopic evaluation. (a) Articular defect fully filled with new cartilage tissue. (b) Flat cartilaginous proliferation and smooth surface compared with normal articular cartilage on the left-hand side (arrow) in the autologous chondrocyte transplantation treatment group. (c) Subchondral bone exposed with small intralesional cartilage island showing a velvet surface. (d) Exuberant fibrocartilaginous proliferation with irregular surface compared with normal articular cartilage on the left-hand side (arrow). (b, d) Stain: hematoxylin and eosin; original magnification: × 40.