Pyogenic granuloma-like reaction in the necrotic, vessels-deprived femoral head of the rat.

Osteonecrosis of the femoral head was produced in rats by cutting the ligamentum teres and incising the cervical periosteum. As of the second postoperative week, fibrous tissue pervaded the necrotic epiphyses, macrophages and osteoclasts removed the debris, osteoblasts deposited lamellar-fibred and woven-fibred intramembranous bone, and remodeling began. In 16% of the rats killed during the 2nd postoperative week, the epiphyses contained big fragments of necrotic bone enclosed by densely packed, capillary-sized vessels. Ingrowth of this hypervascularized, pyogenic granuloma-like tissue is presumably due to the presence of excessive growth factors, reflecting an exaggerated pathophysiological reaction within the framework of organization of the necrotic epiphyses.