Solid Growth: Bone Grafts’ Role in Spine Surgery and Fusion Success
Today’s bone graft options extend beyond your own bones
Bone graft is used in spine fusion surgical procedures. The purpose of bone grafts—and there are many different types—is to enable new bone to grow and heal the spine into a stable structure—often called stabilization. Bone graft material can be placed onto or within the spine to serve as a scaffold or foundation from which new bone grows, fusing/joining bone together during the healing process. After the fusion heals, the spine is stable.
Bone Remodeling: How New Bone Grows
The bone remodeling illustration below may help you appreciate how new bone grows—a vital part of spinal fusion. During the process of bone remodeling, bone cells called osteoclasts break down and help remove old bone. Osteoblasts follow-up by producing a cellular matrix that helps to stimulate new bone cells (osteocytes) to grow and lay down new bone; similar to the way the asphalt of an old road is removed and replaced with smooth, strong new asphalt. The activity of osteoblasts is essential to achieving bone fusion.
Types of Bone Grafts and Graft Products
Medical advances throughout the years have delivered a variety of bone graft and grafting products, some of which are synthetic or use a manipulated version of a natural product. They are generally considered safe and help provide a foundation for the body to produce its own bone.
Autograft is bone taken from your body. Your spinal surgery may involve removing some bone from your spine, and it can be repurposed for bone grafting. Alternatively, bone may be surgically removed from a part of the body other than the spine, such as the hip bone, during a separate procedure (called harvesting).
- Potential Advantage: Autograft contains your own bone cells that can help stimulate new bone growth, called bone remodeling. Autograft may increase fusion success.
- Potential Disadvantage: Harvesting bone from another part of the body (ie, hip bone) is a separate and additional surgical procedure with its own risks such as bleeding and infection. Furthermore, recovery can be is painful.
Image courtesy of Blausen gallery 2014
Allograft is human donor bone obtained from a certified donor bone bank. Healthy human donor bone is tested for diseases (eg, HIV), cleaned, and sterilized before it is sent to your surgeon’s outpatient center or hospital. Allograft has been used for decades.
Bone banks follow stringent selection and processing guidelines to help ensure the allograft is safe, although there is potential risk for disease transmission despite safety measures. The guidelines are established by the US Food and Drug Administration and American Association of Tissue Banks.
Allograft is made available in different forms and sizes, such as morsels, spinal spacers, strips, and wedges.
- Potential Advantage: You may avoid a separate surgical procedure to harvest your own bone, which may help speed recovery. It be used as a bone graft extender when more bone graft material is needed, and can be added to autograft.
- Potential Disadvantage: Allograft does not contain living bone cells, doesn’t stimulate new bone growth and is not as potent as your own bone.
Demineralized Bone Matrix (DBM)
DBM is a type of human allograft. The difference between DBM and other allograft is the mineral has been removed (demineralized) from the bone leaving behind collagens and proteins that help stimulate new bone growth. Demineralized bone matrix is available in many different forms, including powder, crushed granules, putty, chips, or gel.
- Potential Advantage: The risk for disease transmission is very low because the product is highly processed.
- Potential Disadvantage: It does not provide structural strength that may be required in the surgical treatment of certain spinal disorders.
Bone Morphogenetic Proteins (BMPs)
These proteins, produced in the human body, can help speed fusion and may protect against rejection of donor bone and nonbone substitutes. BMP proteins are found in trace amounts in human bone and are produced in larger amounts through genetic engineering.
Ceramics are synthetic bone grafts made from calcium substances. Ceramic-based bone graft extenders are available in different forms, including porous and mesh. They do not contain proteins that promote bone growth, so they are often used in combination with another bone source(s). One disadvantage to ceramics is it may cause inflammation in some patients.
With its unique, porous structure, coral bone implants are used for spinal surgery as a graft extender or to provide a framework for bone to grow into.
How Do Surgeons Choose Which Bone Graft to Use?
The decision of which bone graft material a surgeon chooses to use takes into consideration:
- Patient preference
- Need for immediate structural support
- Anticipated difficulty for that individual patient to grow bone (increasing age, smoking, diabetes, steroid use are all factors that can make it harder to grow bone)
- The surgeon's unique technical preferences
Ever-advancing medical technology has afforded patients undergoing spinal fusion or other type of neck or back surgery a wealth of options when it comes to bone grafts. Every type of bone graft comes with its own set of pros and cons, and your surgeon will discuss your options with you so you can make the right decision for you.