BACKGROUND: Using bone marrow mesenchymal stem cells (MSCs) infected by an adenoviral vector cen-ying human hepatocyte growth factor (HGF) gene, which was independently developed by our laboratory and has been approved by SFDA in clinical trial to repair bone defects via cell therapy.OBJECTIVE: To investigate the bone restoration effect of mssenchymal stem cell and hepatocyte growth factor in the pathophysiological course of femoral head osteonecresis defects.DESIGN, TIME AND SETTING: An in vivo experiment of ceUular-rnatedal science. The experiment was performed at the Beijing Institute of Radiation Medicine and the 66400 Orthopaedic Hospital of Chinese PLA from September to December 2007. MATERIALS: Eighteen New Zealand rabbits with clean grade, aged 26-28 weeks, were supplied by Beijing Kaiyuan rabbit livestock farm. Bone matrix gelatin was purchased from Shanghai Xiaobo Technological Development Limited Co., Ltd. METHODS: MSCs from New Zealand white rabbit were isolated and culture-expanded by adhesion method and their in vitro ostengenesis and adipogenesis were identified. Eighteen New Zealand white rabbits were created femoral heads defect models and randomly divided into 3 groups, with 6 animals in each group. Animals in each group were treated with scaffold of bone matrix gelatin (27 mm3 per defect) only, scaffolds seeded with MSCs (1×107 per defect) or MSCs infected by an adenoviral vector carrying human hepatocyte growth factor gene (MSC/HGF, 1×107 per defect), respectively. Histological examination was conducted at 3 months post operation. MSCs or MSC/HGF were labeled with carboxyfluorescein diacetate succinmidyl ester dye, treated with cobalt chloride for 72 hours and their proliferative status was evaluated and compared by flow cytomatric techniques. MAIN OUTCOME MEASURES: The differentiation of MSCs, therapeutic effect of MSCs in treating femoral head necrosis, and potent ability of MSCs/HGF against hypoxia.RESULTS: The adherent cells could differentiate into osteoblasts and adipocytes under in vitro inductive condition. Histological examination revealed that the bone defects from both control and MSCs-treated groups were fille:d with fibrous tissue, though blood vessels were evident in MSCs-treated group, whereas new bony tissues were obvious in MSC/HGF group. The result was further confirmed by Lane-Sandhu scaling, which indicated that new bone formation was more evident in MSC/HGF-treated group compared with MSCs-treated or control group (P< 0.01). Flow cytometry analysis showed that the proportion of MSC/HGF-treated group that had experienced cell division was significantly higher than that of MSCs-treated group after cobalt treatment (P < 0.001).CONCLUSION: MSC/HGF exhibit greater osteogeneeis in vivo in this model compared their counterparts, which might be attributed to their resistance to hypoxic injury. The results here suggest that HGF gene modification might be an optional strategy for the application of MSCs in the management of avascular osteonecrosis.