The role of bone marrow in bone morphogenetic protein-induced repair of femoral massive diaphyseal defects.

The midshaft of the femur of one-year-old rats was resected and the reparative process completely blocked by distraction of the bone ends with an omega-shaped wire. Bone repair extended retrograde instead of across the diaphyseal defect and invariably culminated in nonunion. New bone was induced to grow across the defect by implantation of BMP, and regeneration was similarly enhanced by transplantation of autologous marrow, but union was produced only by composite transplants of marrow and implants of BMP. Union occurred more rapidly from the transplant-implant composite than from autologous cortical bone. These observations suggest that bone marrow stroma cell include both pre-existing osteogenic precursor cells and mesenchymal cells that respond to BMP by differentiating into osteoblast for the repair of large femoral bone defects.