Histological morphology of femoral articular cartilage with safranin-O staining at contact, transitional, and non-contact areas in the control (CON), low- (LIR), moderate- (MIR), and high-intensity (HIR) groups. Grossly normal histological characteristics of cartilage sections were observed in the CON, LIR and MIR groups, though the increased staining for Safranin O was found in the LIR and MIR groups in comparison with the CON group. Within the CON, LIR, and MIR groups, no distinct difference was found among the contact, transitional, and non-contact areas. In contrast, osteoarthritic histological changes of surface irregularities, cell cloning, and marked reduction in the safranin-O staining were found in the HIR group, with the most severe changes at the contact area. NCA: non-contact area, TA: transitional area; CA: contact area. Scale bar = 50 μm.