Abstract: Objective To observe the relationship between the subchondral plate and cartilage in the osteoarthritic rabbit knee, and to investigate the effect of calcitonin on subchondral plate to protect cartilage. Methods Male rabbits were randomly divided into three groups(8 animals per group)，control, model, and experiment groups. In the model and experiment groups，anterior cruciate ligament transaction (ACLT) operation was carried out in the right knee joint. After that, rabbits in the experiment group received subcutaneous injections of calcitonin with 5 IU/(kgI>&#/I>8226;d) dosage. Rabbits in the model group were injected saline. All the rabbits were sacrificed after ACLT operation for 8 weeks. The paraffin sections were stained with HE and von Gieson and graded by Mankin’s scale. Immunohistochemical expressions of matrix metalloproteinases (MMP-13) in cartilage were detected by integral absorbance (IA) analyses. The histomorphometry was applied to analyse the subchondral plate at the proximal tibia. Results Analyzed by the Mankin`s scale in cartilage, the scores of the model group were significantly higher than that of the control and experiment group( P <0.05) and the scores of the experiment group were markedly higher than that of the control group( P <0.05). MMP-13 immunochemical staining in the model group showed a significant overexpression in comparison with those in the control group and experiment group( P <0.05). There was a strong difference of IA scores between the control group and experiment group ( P <0.05); There were significant differences in volume, thickness and porosity of the subchondral plate among the three groups( P <0.05). Conclusion The structures of the subchondral plate and cartilage were destroyed in osteoarthritic rabbit knee induced by ACLT operation, and there was a strong relationship between the subchondral plate and cartilage. Calcitonin treatment on the subchondral plate in the early stage of osteoarthritis may partialy provide protection on

Key words: Osteoarthritis, Anterior cruciate ligament transaction, Cartilage, Subchondral plate, Calcitonin, Immunohistochemistry, Rabbit