Experimental steroid-induced osteonecrosis in adult rabbits with hypersensitivity vasculitis.

Osteonecrosis (ON) was experimentally induced in rabbits by employing a combined protocol of hypersensitivity vasculitis and administration of high-dose corticosteroids. Thirty-five adult rabbits were used: five were injected twice with horse serum (Group A), five were injected three times with methylprednisolone acetate (Group B), 20 were treated with a combination of horse serum and methylprednisolone acetate (Group C), and five were used as a control (Group D). Both femurs of each rabbit were obtained one to five weeks after the final treatment and were histologically examined. There was no evidence of ON in Groups A, B, and D, whereas vasculitis was prominent in the femurs of Group A rabbits. In Group C, 14 of 20 specimens (70%) showed histologic evidence of ON in the femoral metaphysis: seven showed marrow necrosis and seven marrow and trabecular necrosis. Intramedullary hemorrhage was detected in eight animals. All specimens that showed ON or marrow necrosis revealed arteriopathy (i.e., severe damage to the vascular wall structure of arterioles). These findings were similar to those observed in early ON of clinical materials. The authors conclude that arteriopathy plays an important role in the pathogenesis of ON.