Types of bone grafts. ( A) Autograft: The surgeon harvests bone from another site of the patient's skeleton, often from the iliac crest, and implants it into the bone defect site. This type of bone grafts leads to two surgeries, thus, two scars, more pain, and additional infection risk. ( B, C) Allograft and xenograft: Here the bone graft is obtained from a human donor or animal model, respectively. These types of bone grafts, particularly xenografts, carry the risk of immunologic response and transmission of viral and bacterial disease and with xenografts, zoonotic disease. ( D) Synthetic bone graft substitute: There are different types of synthetic grafts. These biomaterials are safe and need no second surgery site.