Evaluation of synovial fibrosis. After anterior cruciate ligament transection in both knees, 500 ng BMP-7 in 200 μl PBS was injected weekly into the right knee and the same amount of PBS was injected into the left knee. Whole knee sections stained with Masson's trichrome were evaluated at 12 weeks after ACLT. (a, c) Lower magnified histologies. Bar = 5 mm. (b, d) Higher magnified histologies of infrapatella fat pad. Bar = 1 mm. (e) Quantitation of fibrosis in infrapatellar fat pad. The values are displayed as average ± standard deviation (n = 3). BMP, bone morphogenetic protein; F, femur; IPF, infrapatellar fat pad; P, patella; PBS, phosphate-buffered saline; T, tibia.