Bone formation in the fresh autogenous rib graft

Abstract

Cellular mechanism of bone formation in the central portion of a fresh rib which was grafted in a manner to bridge the lower borders of the mandibule was studied in 32 rats.
At one week of the graft, the bone which was undergoing osteoclastic resorption was surrounded by connective tissue containing undifferentiated mesenchymal cells. The bone marrow had been replaced by granulation tissue. Evident osteoblastic bone formation was not observed.
At two weeks, resorption of the grafted bone was still going on, but newly formed bone with osteoblastic lining was seen along the cement line. The newly formed bone was invaded by capillaries and in their vicinity osteoclastic resorption and osteoblastic formation of bone was taking place concurrently. Histochemically, acid phosphatase activity was present in osteoclasts and resorption lacunae in both of the newly formed bone and the grafted bone. In addition cartilage was observed in approximately half of the grafts and it was surrounded by layers of chondroblasts and undifferentiated mesenchymal cells. Matrix vesicles were seen ultrastructually in the areas of newly formed bone and cartilage.
At three weeks the majority of the grafted bone had undergone resorption. Acid phosphatase activity was seen in osteoclasts and resorption lacunae of the grafted bone and adjacent to the osteoclasts. Osteoblasts undergoing active bcne formation were located along the cement line which was continuous to the resorption lacunae, whereas with hypertrophic change of chondrocytes, the cartilage was invaded by vascular endothelial cells and new bone was being formed by osteoblasts.
Injections of EDTA-Pb showed active bone formation at the second and third weeks of the graft.
After the fourth week cartilage was observed in no specimen and the graft had been completely replaced by newly formed bone.
All these findings indicate that the grafted bone is incorporated into newly formed bone either by enchondral ossification or direct bone induction from the grafted bone through coupling mechanism.