Immunohistochemical staining of the sections in experimental (A, C) and control group (B, D) at 12 weeks. Type I and II collagen was visualized by DAB (brown) staining. (A) The staining of type II collagen in repair tissue (R) was strong and similar with that of adjacent cartilage (C). (B) The matrix of the repair tissue (R) was stained slightly. (C) Almost no type I collagen staining was detected in the repair tissue (R) of group 1. (D) Intense type I collagen staining was observed in repair tissue (R) of group 2. All the images are magnified 20X.