Effects of PAM treatment on cartilage surface erosion. The sections were stained with safranin-O (red stain) for glycosaminoglycans, rapid green for bone. (a) The Sham group had no erosion-like changes in the cartilage surface. (b,c) Short-term and long-term treatment with PAM significantly increased chondrocytes and matrices, while fibroses of the cartilage surface were significantly reduced compared with the ACLT group at 6 and 14 weeks. (d) ACLT group at 2 weeks, no significant changes were observed in the cartilage surface. (e) ACLT group at 4 weeks, staining of safranin O had been partially lost and various degrees of surface fibrosis, cracks, cell loss proliferation were observed in the surface layer of the hyaline cartilage. (f,g) ACLT group at 6 and 14 weeks, chondrocytes of the hyaline cartilage surface were massively reduced, fibroses were extensive, osteophytes had formed, vertical fractures had increased and safranin O staining in the cartilaginous area was significantly reduced. Bar represents 200 μm.