Hemorrhage and thrombus formation in early experimental osteonecrosis

The aim of the current study was to test the hypothesis that the induction of an underlying immunologic condition in rabbits may enhance the developme nt of steroid-induced osteonecrosis. Thirty-five adult rabbits were divided into four groups. Group I: 10 rabbits were immunized at 15-day intervals f or 2 months by murine antibodies to deoxyribonucleic acid autoantibodies. F our weeks after the end of the immunization, the animals received injection s of methylprednisolone for 7 days and then prednisolone per os for 8 month s. Group II: 10 animals only received immunizations according to the protoc ol used in Group I. Group III: 10 animals only were treated with corticoste roids according to the protocol used in Group I. Group IV: five animals wer e used as controls. Various changes were observed in the proximal metaphysi s and diaphysis of the femur in eight of 10 animals in Group I (80%) and in five of 10 animals in Group II (50%) when compared with the animals in Gro up III and Group IV. The most common feature was evidence of new and old he morrhage through the sinusoids, exudative reaction and thrombus formation i n veins and small arteries. Focal necrotic areas of bone marrow showed an a ccumulation of cell debris, residue of hemorrhage, and disappearance of mar row elements. These findings suggest that (1) corticosteroids may potentiat e the effects of a preexisting condition to increase the risk of osteonecro sis; (2) immunologic reaction may be an important factor in the pathogenesi s of necrotic lesions; and (3) repeated intramedullary hemorrhage and throm bus formation may represent early major pathologic findings in bone necrosi s.