A basic part of any spinal fusion surgery is the use of bone graft. Bone grafting is used for many types of orthopedic procedures that require bones to heal. In spine surgery, bone grafting stimulates healing and provides support to the spine by filling gaps between two bones.
Bone graft is used to stimulate and speed the fusion healing process. Bone can be crushed into powder and placed around a fusion site. Chemicals in bone graft stimulate nearby bones to heal. If the bone is taken from the person's own body, there may also be osteocytes (living bone cells) that survive the transfer to do their intended work of making new bone. Even bone taken from someone else can stimulate bone healing.
Bone graft is also used for structural support for fusion. Larger pieces of bone may be used to fill a gap between two bones. For example, in a fusion surgery the surgeon removes an intervertebral disc and may place a chunk of bone graft into the now empty space. Over time the entire piece of bone that was grafted will be "remodeled" and replaced by the body with new bone. The time it takes to fuse depends on the size of the piece of bone that was used. It is sometimes a slow process that may take several years.
A common approach for bone grafting is to use your own bone whenever possible. Bone taken from your own body is called autograft. Bone can be removed from the area being operated on and used for the fusion. Bone graft taken from someone else is called allograft. The surgeon may mix allograft with autograft. Allograft can come from many types of bones in many different forms. Allograft is usually removed from organ donors and placed in bone banks. Bone banks make sure the bone graft is sterile by testing it for diseases such as hepatitis and AIDS, just like testing in a blood bank. Even though allograft bone is rigidly tested, it carries a very small risk of contracting a disease from the allograft bone. Advantages include not harvesting extra bone from the patient, which potentially means a shorter surgery with less post-operative pain. The disadvantage of an allograft is that new bone may not always grow as well or as quickly. In those cases, a bone-growing protein can be added to the area to make up for what the bone graft naturally lacks. Allograft is very useful when the operation requires more bone graft than your own body can supply.
There is growing research in progress to design bone graft substitutes, chemicals, and devices that stimulate bone fusion. It is well known that electrical current stimulates bone growth. Surgeons can use electrical stimulation devices during the first weeks of surgery to encourage fusion. Several artificial bone graft materials have been developed and your surgeon will discuss whether use of these materials would be beneficial.