Objective: To investigate the incidence of steroid-induced osteonecrosis (ON) among male and female rabbits. Methods: Forty-seven adult rabbits (male, n = 24; female, n = 23) were injected once intramuscularly into the right gluteus medius muscle with 20 mg/kg of methylprednisolone acetate. Haematological examinations were performed just before and at 1 and 2 weeks after the steroid injection. Two weeks after the injection, both femora and humeri were histopathologically examined for the presence of ON, and the bone marrow fat cells were examined morphologically. Results: Sixteen of 24 male rabbits (66.7%) and 5 of 23 female rabbits (21.7%) developed ON. There was a significant difference in the rate of incidence of ON between male and female rabbits (P = 0.0032). Haematologically, at 1 week after the steroid injection, both the mean low-density lipoprotein (LDL) and the ratio of LDL cholesterol to high-density lipoprotein cholesterol in the male rabbits were significantly higher than those in the female rabbits (P = 0.0001 for both comparisons). The bone marrow fat cells of the male rabbits [61.5 (5.6) μm] were significantly larger than those of the female rabbits [58.9 (3.7) μm; P = 0.0102]. Conclusion: This study indicates that gender may be an important factor in considering the pathogenesis of steroid-induced ON.
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