Histological findings of the knee joint at 12 weeks. (A) Hematoxylin and eosin staining and safranin O staining: the injured site in the miR-210 group was morphologically healed whereas the tear in the meniscus still remained in the control group (bar = 100 μm). Safranin O staining revealed that the degeneration of articular cartilage in the miR-210 group was lower than that of the control group. Arrow, injured site. Upper panels, best result; lower panels, worst result. (B) Meniscal healing score in the miR-210 group (3.0 ± 0.0 points) was significantly higher than in the control group (1.3 ± 0.6 points) (*P < 0.05, n = 6 for each group). Degenerative change of cartilage in the control group was more advanced than in the miR-210 group. (C) Mankin score in the miR-210 group (1.0 ± 0.4 points) was significantly lower than in the control group (5.6 ± 1.4 points), showing a significant difference between the two groups (*P < 0.05, n = 6 for each group). Intra-articular injection of miR-210 prevented articular cartilage degeneration.