A comparison of osteocyte bioactivity in fine particulate bone powder grafts vs larger bone grafts in a rat bone repair model

The osteogenic potential for bone grafts is based on numbers and activities of cells that survive transplantation. In this study, we compared the bioactivity of osteocytes in 300–500 μm fine particulate bone powder grafts to 2 mm larger bone grafts in a rat radial defect model. Expression levels of bone morphogenetic protein-2 (BMP-2), transforming growth factor-beta 1 (TGF-β1), alkaline phosphatase (ALP), and collagen I were semi-quantified by both immunohistochemistry and RT-PCR at days 1 and 4, as well as weeks 1, 2, 4, 6 and 10 post-transplantation. Within two weeks post-transplantation, more cells stained positively for BMP-2, TGF-β1, ALP, and collagen I within the bone grafts and in the surrounding tissues in the group transplanted with the fine particulate bone powder grafts than in those with larger bone grafts (P < 0.05). The mRNA levels of all four markers in the group transplanted with fine particulate bone powder graft peaked earlier and were expressed more highly than in the larger bone graft group, suggesting that fine particulate bone powder grafts provide more viable and active osteocytes to accelerate bone defect healing than larger bone grafts.