Bone Grafts and Substitutes in Fracture Repair – Part 2

Osteogenesis: Direct Bone Formation

The osteogenic properties of a bone graft determine its ability to generate new bone tissue from the graft itself. Osteogenic grafts contain the osteoprogenitor cells, growth factors and matrix that are required to form new bone.

• Fresh autografts and bone marrow aspirates retain living osteoblasts or MSC, enabling direct new bone formation.

• Allografts and synthetic materials lack osteogenic cells but can support bone formation when paired with osteoinductive signaling molecules (1-4).

Osteoinduction: A Key Step in Activating Bone Formation

Osteoinduction refers to the ability of a graft to stimulate osteoprogenitor cells such as mesenchymal stem cells (MSC) to differentiate into bone-forming osteoblasts and chondroblasts, leading to new bone formation. This process is regulated by factors that orchestrate cell differentiation, proliferation, growth, and matrix deposition, including:

• Bone Morphogenetic Proteins (BMP)

• Fibroblast Growth Factors (FGF)

• Platelet-derived Growth Factor (PDGF)

• Vascular Endothelial Growth Factor (VEGF)

• Others

Osteoconduction: Providing a Scaffold for Growth

Osteoconduction refers to the ability of the graft to serve as a scaffold, allowing new bone cells to adhere, proliferate, and integrate with the patient’s existing bone. As discussed in our last post, BGS with osteoconductive properties include:

• Porous ceramic-based substitutes like hydroxyapatite and β-TCP that provide structural support while permitting cell infiltration.

• Bioactive materials like synthetic polymers that encourage capillary formation and cellular migration.

• Next-generation synthetic carbohydrate polymers, like Osteo-P® BGS, that support cell and vascular infiltration, and sequester the patient’s own osteoinductive factors for bone formation.