Objective To observe microvascular changes in hormone-induced bone necrosis and also to study the mechanism of hyperbaric oxygen (HBO) in the treatment of femoral head bone necrosis.Methods Forty-eight adult Japanese white rabbits were randomly divided into 2 groups:the experiment group (n =36) and the control group (n =12).The animals in the model group (or the experimental group) were injected with 10mg/kg of prednisone acetate,twice a week for a duration of 6 weeks,while the animals in the control group were injected with 2 ml of normal saline,also twice a week for a duration of 6 weeks.Then,the rabbits in the experimental group were randomly divided into the HBO group (n =17) and the control group (n =17).The HBO group received HBO treatment,for 6 successive weeks,while the control group breathed normal fresh air.At the end of 2,4,6,8,10 and 12 weeks after experiment,blood rheology,vascular endothelial growth factor (VEGF),pathological changes in the tissue involved and radiological imaging changes were observed closely.Results At the end of the 2nd week,4th week and 6th week after experiment,features of hemorheology in the model group deteriorated.The animals of the model group developed endangium,thrombosis,osteoporosis of the femoral head,increased numbers of empty bone lacunae and fat cells,rupture of certain bone trabecula,volume reduction of bone cells of the femoral head and quite a few bone cells were seen to be dead and dissolved into fragments under the electron microscope.In the HBO treatment group,hemorheologic features tended to be better,positive expressions of VEGF could be seen in the osteoblasts on the bone trabecula surface and blood vessels as well,and positive expressions were mainly detected in endangium.Repair of necrostic bone cells to some extent could be seen under the light microscope,and neogenetic bone cells could also be seen under the transmission electron microscope.Conclusions Large dosage of hormone could induce damage to endangium,which might be the main cause of avascular necrosis of the femoral head.HBO could accelerate the processes of vascular regeneration and bone ossification through the expressions of VEGF and other cytokines and promote bone repair,which might provide an important theoretical evidence for the treatment of hormone-induced bone necrosis of femoral head.