Bone grafts help bones heal. Common cases that may require a bone graft include severe fractures, jaw reinforcement before dental implants, areas of missing bone due to disease such as cancer or bone infections, spinal fusion procedures, and artificial joint replacement surgeries.

Bone grafting is a dental, spinal, or orthopedic surgical procedure in which a bone replacement material is physically added to the area of missing bone. The goal of bone grafting is to have the patient’s own bone cells grow into the replacement material over time, eventually creating strong, healthy bone.

What is a synthetic bone graft?  

Bone grafting material comes in many forms and from different sources. Natural sources include the patient’s own body, bone tissue from another human body (usually cadavers), or tissue from an animal. Synthetic bone graft material is manufactured in a lab setting and includes polymers, ceramics, metals, and composites. The most successful synthetic bone graft materials are those substances that mimic and closely resemble human bone scaffolding. These biomaterials are often porous, calcium-based substances such as calcium phosphates. Hydroxyapatite (HA) is a calcium phosphate that’s particularly suited to synthetic bone grafts thanks to its biocompatibility and osseointegration abilities.

Defining common bone graft terminology

Bone graft materials from different sources have specific terminology. Further bone grafting terms refer to the desired biological interaction between bone grafts and the patient’s native bones.  

• Autograft: As the prefix “auto” suggests, an autograft is derived from the self, or the patient’s own body. Typically, a small portion of bone is surgically removed from an area of the body. This area is often the top of the pelvic bone, or iliac crest, but can also come from leg bones (often the fibula), spine, the jaw, and the ribs. 

• Allograft: Since “allo” means other, it makes sense that an allograft comes from another human. Generally this is bone material harvested from living donors, such as patients undergoing a hip replacement, or from cadavers.

• Xenograft: The third natural source of bone graft material comes from animals, quite often from bovines.   

• Calcium Phosphate: A porous, naturally occurring mineral, made up of the same mineral components as bone. As a synthetic bone grafting material, calcium phosphate, is highly biocompatible due to its porosity and compatibility with bone.

• Hydroxyapatite: A highly crystalline calcium phosphate compound that’s well suited to bone grafts and cements. 

• Osseointegration: The root word “osseo” refers to bone. Osseointegration happens when living bone tissue fuses and assimilates with another element, such as an osseointegrated implant. In the case of bone grafts, osseointegration refers to the integration of the grafting material with native bone. 

• Osteogenesis: The formation of bone, which is necessary for bone replacement treatments. 

• Osteoinduction: A process that inspires osteogenesis. Generally, the human body naturally undergoes osteoinduction to repair a damaged bone. In the case of bone grafting, if the grafting materials are osteoinductive they will induce the body to generate new bone tissue. 

• Osteoconduction: A situation in which native bone grows on the surface of another material, such as around an implant. In bone grafting, osteoconduction happens when the bone graft acts as a scaffolding across which new bone cells form, eventually replacing the graft material.
  
  

Autograft vs allograft vs synthetic bone graft material

There are benefits and drawbacks to both natural and synthetic bone grafts. Autografts have the benefit of coming from the patient's own body. Factors such as biocompatibility and osseointegration are greatly improved as the material is not seen as foreign and the chance of disease or pathogen transference from another source is eliminated. However, autografting requires the removal of bone, which can be painful, takes time to heal, and subjects the patient to complications of a second surgery (in addition to the bone graft surgery). The amount of healthy bone tissue that can be removed from the patient’s own body is, obviously, limited. 

Allografts solves most of the drawbacks of an autograft, but comes with its own set of considerations. Allograft material can come from fresh-frozen cadavers or in the form of freeze dried bone matrix. If the tissue comes from a cadaver, the amount that may be harvested is far less limited. A second surgery is also not required.  Compatibility and immunogenic rejection issues can sometimes arise when using bone graft material harvested from another person. Allografts have also resulted in slower osseointegration. 

Like allografts, synthetic bone grafts eliminate the risks of an additional operation on the patient. As a completely sterile material, the risk of introducing human pathogens is completely eliminated, which is a small risk with allografts. Like human bone material, synthetic bone graft material has osseointegration and osteoconduction properties. Bioactive synthetic bone graft materials have been shown to have osteoinduction properties on par with autografts, especially when chemical composition and particle structure are optimized.

Osteoinductive vs osteoconductive 

The end goal for all bone grafting procedures is the regeneration of healthy bone where there had previously been a void, damage, or disease. Both osteoinduction and osteoconduction play a role in this desired outcome, but the terms have slightly different meanings and play different roles in the bone grafting process. 

In the simplest terms, you can think of osteoinduction as the process by which osteoconduction occurs. As mentioned above, complete osteoconduction in bone grafts occurs when the patient’s own bone cells have fully replaced the grafting material with living bone tissue. That can’t happen if the cells surrounding the bone graft material are not inspired to create osteogenic (or bone-forming) cells. Osteoinduction happens because the grafting material, in contact with nearby cells, induces them to create bone cells (as opposed to other tissue) and begin the process of regenerating bone.

As osteoconduction is the goal, it’s extremely important that the bone graft material be capable of osteoinduction. Autograft bone has the benefit of supplying its own osteogenic cells, from the patient’s own body, that lead to osteoinduction. Allograft materials also contribute to osteoinduction as they still contain bone morphogenetic proteins to stimulate bone growth.

Osteoinductive synthetic bone graft materials

Synthetic bone graft materials can be made from a wide variety of materials, including polymers, ceramics, bioglasses, metals, and composites. Critically for osteoinduction, bone graft materials made from calcium phosphate ceramics are bioactive and have the ability to induce cellular responses in nearby tissue. Factors such as porosity, surface chemistry, and surface morphology all have an effect on nearby cells and encourage osteroinduciton and eventual osteoconduction.

As manufacturers of pure, bioactive calcium phosphates, Himed works with members of the orthopedic and dental industries to produce effective bone graft materials to nearly any specification.