Best, mean and worst results of safranin O staining in experimental (A, C and E) and control group (B, D and F) at 12 weeks. (A) The repair tissue showed homogenous intense safranin O staining. Tidemark formation was observed, and subchondral bone formation was good. The surface was not smooth, with fibrous tissue existing. (C) The staining of the repair tissue was homogenously intense. No fissues or cracks were seen. But, no tidemark formation was observed. (E) Subchondral bone formation was poor with a large crack in the center of the repair tissue. But, safranin O staining was still intense in the extracellular matrix (ECM) of the repair tissue. No tidemark formation was found. (B) The ECM of the repair tissue was stained slightly and heterogeneously. The surface was not regular. No tidemark formation was seen. Subchondral bone formation was not good. (D) The repair tissue was stained negatively. No tidemark formation was seen, and subchondral bone formation was poor. (F) Little subchondral bone was seen. Safranin O staining was negative in the ECM of the repair tissue. All the magnification was 20X.