I heard a talk at our hospital about why we are moving more toward using bone graft substitutes. I'm just a nurses aid on the orthopedic floor, so I really didn't understand it all. They said these new substitutes are inductive and conductive. After that they lost me. What does that mean? And why is it better than using your own bone?

There are different reasons to fuse the spine and different ways to do the fusion procedure. Surgeons are studying the results of fusion techniques to get an idea of which one works best for each problem. Fusing two or more vertebral bones together prevents motion at those segments and stabilizes the spine. Instrumentation such as screws or metal plates and screws may be used to perform the fusion. Bone grafting using the patient's own harvested bone or bone from a bone bank (either without instrumentation) is another approach.

More recently, bone graft substitutes have come onto the scene. These materials made from bone are called recombinant human bone morphogenetic proteins (rhBMP). There are two types of recombinant BMPs available: rhBMP-2 and rhBMP-7. BMP bone graft materials rely on growth factors within the bone to do two things: make more bone cells (osteoinductive) and build a scaffold for the new bone cells to live (osteoconductive).

Bone graft materials are useful because they eliminate the risk of rejection with donor bone and the risk of infection at the donor site with patients who have donated their own bone. There are other potential problems with using patient-harvested bone for the graft. For example, the donor site can be very painful or sore for a long time. It takes time in the operating room to gain access and then remove the donor bone, which can increase the risk of complications. And then after all that, the bone graft may fail and the patient ends up with a nonunion fusion. In other words, the vertebral bones still move when they shouldn't so the spine still isn't stable.

Bone cells from a bone bank are really only osteoconductive -- they provide a framework for the body to fill in with its own live bone cells. The donated bone is no longer alive, so it is not osteoinductive (able to make new bone cells). That's where bone substitutes like bone morphogenetic proteins (BMPs) come in handy. BMPs contain both the bone mineral matrix and growth factors, which makes them osteoconductive (provides a scaffold) AND osteoinductive (helps fill the scaffold in with new bone).

Rajender Agarwal, MD, MPH, et al. Osteoinductive Bone Graft Substitutes for Lumbar Fusion: A Systematic Review. In Journal of Neurosurgery: Spine. December 2009. Vol. 11. No. 6. Pp. 729-740.

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