[The effect of steroid use on the pathogenesis of avascular necrosis of the femoral head: an animal model].

Objectives: We investigated the effect of corticosteroid treatment on the femoral head of healthy and serum disease-induced rats.

Methods: Thirty Sprague-Dawley rats weighing 250-300 g were divided into three groups equal in number. In group A, serum disease was induced by two intraperitoneal injections of sterile human serum (10 ml/kg), interspersed with a two-week interval. The rats were then treated with methylprednisolone (40 mg/kg/day) for three consecutive days two weeks after the last injection. In group B, the animals received only methylprednisolone (40 mg/kg/day) for three days. In group C (controls), the same procedures were applied as those in group A, but with saline solution alone. All the rats were sacrificed two weeks after the last procedure. The left and right femora were sectioned axially and sagittally, respectively, to be examined under light microscopy with respect to vasculitis, hemorrhage in bone marrow, and changes in cell morphology.

Results: Histological examination showed decreased bone marrow, necrotic areas, diffuse hemorrhage, lacunae, and small areas of osteonecrosis in group A rats. Necrosis in the smooth muscle of the arteriole walls, and degenerative changes in the tunica media were suggestive of vasculitis. In group B, major findings were cellular differentiation of bone marrow, without findings of osteonecrosis in bone trabeculae. In the control group, no pathologic findings were observed other than intramedullary hemorrhage.

Conclusion: Even though it is not the main cause of bone necrosis, steroid administration increases the risk for avascular necrosis of the femoral head.