[An animal model of Perthes disease and an experimental research of VEGF expression].

OBJECTIVE: To make a rabbit model of Perthes disease and to explore the change and its significance of VEGF expression in the femoral head.

METHODS: Twenty-four 3-month-old New Zealand rabbits (weighing 1.6-1.8 kg) were randomly divided into experimental group (n=16) and control group (n=8). A rabbit model of Perthes disease was made by excision of left ligamentum teres and retinacular blood supplies of femoral head. The gross appearance, X-ray film and histological observations were made and the immunohistochemistry and VEGF mRNA in situ hybridization were carried out 1, 2, 4, 8 weeks after operation.

RESULTS: The rabbit model of Perthes disease was made successfully; only 1 was infected 5 days after operation and was made quit. The gross appearance: The femoral heads had no necrosis changes in control group at every time. The femoral heads became coarse, tarnish and smaller, and even collapsed in experimental group. The HE staining observation: The femoral heads had no necrosis changes in control group at every time after operations. New vessels and granulation tissues grew into the necrosis part in the experimental group 4 weeks and 8 weeks after operations. New bone could be seen in repaired bone. Immunohistochemistry staining: In the epiphyseal cartilage of the femoral heads in control group, an intensive VEGF immunoreactivity (VEGF-IR) was found in the hypertrophic zone with a low level of VEGF-IR in the proliferative zone. At 1 week after operation, the percentage of VEGF+ cells in the proliferative zone of the femoral heads in experimental group was increased compared with that of the femoral heads in control group. The percentage of VEGF+ cells in the hypertrophic zone of the femoral heads in experimental group was significantly decreased compared with that of the femoral heads in control group. At 8 weeks after operation, VEGF-IR was observed throughout the epiphyseal cartilage surrounding the bony epiphysis in the femoral heads in experimental group. The percentage of VEGF-positive cells in the proliferative zone of the femoral heads in experimental group was significantly increased compared with that of the normal heads. The hypertrophic zone of the femoral heads in experimental group had a similar percentage of the VEGF+ cells to the femoral heads in control group when endochondral ossification was restored at 8 weeks. There were statistically significant differences in the ratios of VEGF+ cells in the proliferative zone of femoral head 1, 2, 4, 8 weeks after operations (P < 0.01); in the ratios of VEGF+ cells in the hypotrophic zone of femoral head 1, 2, 4 weeks after operations (P < 0.01) between experimental group and control group. In situ hybridization results: The results were similar to that of histology. VEGF mRNA expression in the hypertrophic zone of epiphyseal cartilage after necrosis were lower. VEGF mRNA expression in the proliferative zone of epiphyseal cartilage after necrosis increased. VEGF mRNA expression in the hypertrophic zone of epiphyseal cartilage in experimental group could be seen again after endochondral ossification was repaired.

CONCLUSION: It is possible that VEGF may act as a key regulator that couples angiogenesis, cartilage remodeling, and ossification after ischemic damage to restore endochondral ossification in the epiphyseal cartilage.