Bone grafting is a surgical procedure used to repair complex bone fractures, fuse joints, or replace bone volume lost due to trauma, disease, or surgery. The fundamental purpose of any bone graft material is to act as a physical scaffold, providing a supportive structure that guides the body’s natural regenerative processes. This scaffolding function, known as osteoconduction, allows new bone cells and blood vessels to migrate into the area and form new, native bone tissue. The composition of the graft material determines its biological behavior and effectiveness in promoting healing.
Materials Sourced From the Patient (Autografts)
Autografts are bone materials harvested directly from the patient’s own body, often from sites like the iliac crest (hip), fibula, or ribs. This material is regarded as the “gold standard” because it is the only type of graft that contains living bone cells, giving it osteogenic properties. The graft is composed of the full biological matrix, including bone cells (osteocytes), structural proteins like collagen, and a rich supply of growth factors.
Because the bone is genetically identical, there is no risk of immune rejection or disease transmission. The living cells actively contribute to the bone repair process, leading to a predictable outcome and faster healing. Natural growth factors, such as bone morphogenetic proteins (BMPs), also give autografts strong osteoinductive properties, encouraging undifferentiated cells to become bone-forming cells. However, harvesting the graft requires a secondary surgical site, which introduces the possibility of pain, complications, and a longer recovery time.
Donor and Animal-Based Materials (Allografts and Xenografts)
Materials sourced from human donors are called allografts; those from animal sources, typically bovine or porcine, are known as xenografts. Since these materials come from an external biological source, they must undergo extensive processing to eliminate the risk of disease transmission and prevent an immune reaction. This preparation renders the final graft material non-living, meaning it lacks the osteogenic cells found in autografts.
Allografts, sourced from deceased human donors, are commonly prepared as freeze-dried bone allograft (FDBA) or demineralized bone matrix (DBM). DBM is created by using acid to remove the inorganic mineral content, leaving behind the organic collagen matrix, which exposes naturally occurring growth factors like bone morphogenetic proteins. This demineralization process enhances the graft’s osteoinductive potential, while FDBA primarily functions as an osteoconductive scaffold.
Xenografts, often derived from bovine bone, are subjected to high heat and chemical treatment to completely remove all organic and cellular components, leaving behind only the mineral structure. The resulting material is a highly purified mineral scaffold, primarily composed of hydroxyapatite, which is the main mineral component of human bone. This processing leaves a sturdy, non-living framework that acts purely as an osteoconductive bridge for the patient’s new bone to grow across.
Manufactured and Synthetic Materials (Alloplasts)
Alloplasts are entirely man-made, synthetic materials designed to mimic the structural and chemical composition of natural bone. These manufactured alternatives eliminate the need for a donor site or biological sourcing, making them readily available and consistent in composition. Their function is primarily osteoconductive, acting as a scaffold for new bone growth to migrate into, and they are not inherently osteoinductive or osteogenic.
The chemical composition of alloplasts is dominated by calcium-based ceramics, which closely resemble the inorganic mineral phase of bone. The most common components include hydroxyapatite (HA) and tricalcium phosphate (TCP), which are often used alone or in combination as a biphasic calcium phosphate (BCP). Hydroxyapatite is chemically stable and has a calcium-to-phosphate ratio similar to native bone, which allows it to integrate well, though its high stability means it resorbs very slowly in the body.
Tricalcium phosphate, particularly the beta-tricalcium phosphate (B-TCP) form, is more soluble and designed to resorb more quickly, allowing the body to replace the synthetic scaffold with native bone over a period of months. Other synthetic options include bioactive glass, which can chemically bond with surrounding tissue, and bio-resorbable polymers, which degrade over time. These materials are engineered to degrade at a rate that matches the pace of new bone formation, ensuring the repair site maintains structural support throughout healing.