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BACKGROUND: For the therapeutic purpose, glucocorticoids have been widely used in clinic, resulting in an increased risk of steroid-induced avascular necrosis of the femoral head (SANFH). However, the detailed pathogenesis of SANFH is not yet clear. Internal heat-type acupuncture therapy has a good clinical effect in the treatment of SANFH, but its specific mechanism has not been clearly analyzed. OBJECTIVE: To explore the effect of internal heat-type acupuncture on the expression of osteoprotegerin and nuclear factor kappa B receptor activator ligand (RANKL) in SANFH femoral head tissue. METHODS: Thirty healthy Sprague-Dawley rats without specific pathogens were randomly divided into blank group (n=10) and model group (n=20). The SANFH model was made by methylprednisolone combined with Escherichia coli endotoxin. After successful modeling, the model rats were further randomly divided into model group (n=10) and treatment group (n=10). In the treatment group, the bilateral buttocks of Sprague-Dawley rats were treated with internal heattype acupuncture once a week for 20 minutes, and the temperature was set at 42 °C. Both the blank group and the model group were not given any treatment. The general state and behaviors (number of voluntary activities and holding power) of Sprague-Dawley rats were detected before and after intervention, and the bilateral femoral heads of rats were taken after 4 weeks of intervention. The histomorphological changes of the rat femoral head were observed by hematoxylin-eosin staining and the rate of empty lacunae was calculated. The mRNA and protein expressions of osteoprotegerin and RANKL in the femoral head tissues of each group were detected by real-time fluorescence quantitative PCR, immunohistochemical staining and western blot, respectively. RESULTS AND CONCLUSION: The behavioral scores of rats in the model and treatment groups were significantly lower than those in the blank group (P < 0.01). After intervention, the behavioral scores of rats in the treatment group were significantly higher than those in the model group. Compared with the blank group, the histomorphology of the femur became significantly worse and the rate of empty bone lacuna was significantly higher in the model group (P < 0.001). Compared with the model group, the histomorphology of the femur was significantly improved and the rate of empty bone lacuna was decreased in the treatment group (P < 0.05). Compared with the blank group, the expression levels of RANKL protein and mRNA in the rat femoral head tissue were significantly higher in the model group, while the protein and mRNA expression levels of osteoprotegerin were significantly lower in the model group (P < 0.001). After intervention, the expression levels of RANKL protein and mRNA in the rat femoral head tissue in the treatment group were significantly lower than those in the model group, while the protein and mRNA expression levels of osteoprotegerin were significantly higher than those in the model group (P < 0.05). To conclude, internal heat-type acupuncture may up-regulate the expression of osteoprotegerin, down-regulate the expression of RANKL, and inhibit the function and activity of osteoclasts, thus inhibiting bone resorption and promoting new bone formation and bone tissue repair. [ABSTRACT FROM AUTHOR]