In this review article, the history and development of bone grafting is presented. Spinal fusion requires the use of bone graft material. Usually bone is taken from the patient’s own pelvic bone. This is called an iliac crest autograft. This type of bone graft material has been done since 1911. It remains the preferred choice or gold standard for posterior spinal fusions.
In 1965, scientists discovered bone morphogenetic proteins (BMPs). Studies now show that BMPs can help bone growth and fusion just as well as iliac crest autografts. Research has been able to identify three ways the biology of bone works.
First is osteoconduction. This refers to the way bone graft material builds a scaffold. This scaffold is the framework for bone to fill in around the area in need of new bone growth for bone fusion. Donor bone from cadavers, coral, and ceramics are examples of osteoconductive materials.
Allograft is the most common osteoconductive material. The bone is taken from a cadaver (donor after death). It works best when used as a graft extender. For example, the surgeon may take a damaged or diseased vertebral bone out of the spine. It is replaced with a titanium cage. The patient’s bone is crushed and put back inside the mesh cage. Allograft materials are then placed around the fusion site for its osteoconductive abilities.
The second type of cell that helps bone growth is called osteopromotive. These materials don’t build a scaffold. Instead, they have several growth factors that help enhance the fusion process once it’s already started. Studies have shown that osteopromotive substances don’t help spinal fusion and may even inhibit fusion.
The third bone-making process is called osteoinduction. This refers to the fact that some materials can actually cause new bone to form where bone doesn’t already exist. Autograft bone and the new BMPs fall into this category. Studies show the best fusion results occur when combining autografts with BMPs. Together, these materials give a 97 per cent fusion rate in the spine.
Research is ongoing to find better ways to use BMPs. The authors predict that it’s only a matter of time before BMPs replace autografts as the gold standard in spinal fusions. There’s less blood loss, shorter time in the operating room, and no pain or problems at the graft site.