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Scoliosis Surgery

Bone Graft

The Allograft - is defined as a tissue graft between individuals of the same species (i.e., humans) but of non-identical genetic composition. The source is usually cadaver bone, which is available in large amounts. This bone however has to undergo many different treatment sequences in order to render it neutral to immune reactions and to avoid cross contamination of host diseases. These treatments may include irradiation, freeze-drying, acid washing and other chemical treatments. In the U.S. virtually all donors are being pre-screened for infectious diseases before their bone is even accepted into the tissue banks. After that the processing of the bone would eliminate virtually any chance of cross-infection.

The Xenograft - is defined as a tissue graft between two different species (i.e. bone of bovine origin). Tissue banks usually choose these graft materials, because it is possible to extract larger amounts of bone with a specific microstructure (which is an important factor for bone growth) as compared to bone from human origin.

The Alloplast - usually includes any synthetically derived graft material not (coming) from animal or human origin. In Oral Implantology this usually includes Hydroxyapatite or any formulation thereof.

The Growth Factors are natural proteins found in our bodies that stimulate growth of certain tissues. With respect to bone, genetic engineers have been able to isolate and clone Bone Morphogenic Proteins (BMPs), which have been shown to induce tremendous bone growth in many animal and recently human clinical studies. BMPs may very well become a potential substitute for autogenous graft material for certain applications in the future; however, these substances still need to pass FDA approval.

Each of the bone graft materials is usually developed with a specific purpose or advantage in mind. Some claims made by tissue banks about a certain bone graft material may sometimes have to be taken with a grain of salt, until independent research can verify those claims. The main purpose of using the latter four of the above graft materials is usually to avoid a secondary surgery for harvesting autogenous bone. Your surgeon will make a decision with respect to the bonegraft material, based on your individual needs and the latest research in that field.

The "gold standard" for bone graft has traditionally been autogenous bone graft, generally taken from the patient's own iliac crest ("hip") through a separate incision. Fusion rates using this bone are generally felt to be around 90% for one-level fusions. If an anterior plate-screw system is also used, several studies have shown that the fusion rate may be slightly higher, between 95% and 100%. For two level surgeries the fusion rates with autogenous (patient's own) bone graft are from 75%-85% range without plates, and 90%-100% if plates are used.

In studies of one level anterior cervical fusions, allograft led to fusion in 73%-95% of cases without plates, and in 88% of cases with a plate. Two level cases with allograft and no plate showed disappointing fusion rates of 38%-62%, but adding anterior plates improved the fusion rate to 75%.

Percentages such as these merely indicate what is likely, not what will definitely happen in your case. Even if some studies report a 100% fusion rate using a certain technique, that does not mean that you are guaranteed a fusion with that same technique. Also, a solid fusion on x-ray is not the same as relief of your symptoms.

Harvesting bone from the iliac crest is not without risks. Although most patients have either no problems or slight discomfort from their bone graft donor site, some people do develop complications that may make you choose not to consider using your own bone as graft material. Everyone has additional pain from the bone graft site, and may have to stay in the hospital an extra day. It is common to have discomfort when walking, since some of the hip muscles you use for walking are detached from the iliac crest so the bone graft can be harvested. These muscles are then sewn back into place.

More significant complications resulting from iliac crest harvest are reported in various studies at between 9%-20%, including infection, hematoma (collection of blood), fracture, and sensory (feeling) nerve injury. One study reported that 2.8% of patients who had iliac crest grafts required reoperations because of these complications.

In order to avoid the problems of harvesting autogenous bone graft, many surgeons have recommended that their patients use allograft (banked bone) since there are no donor site complications, no problems with walking, no hip pain, and generally shorter hospital stays when allograft is used. If allograft had the same fusion percentages as autograft, the decision would obviously be very easy. Although allograft leads to fusion in a high percentage of cases, it does not work quite as well as the patient's own autograft bone.

Using your own bone clearly leads to a higher fusion rate, but there is the added risk of a problem related to the iliac crest donor site. Allograft avoids the problems associated with taking a bone graft from the pelvis, but the trade-off is a somewhat lower fusion rate. As we learn every day of our lives, there are pluses and minuses to most of our decisions. Success and complication rates often vary from the "average" for individual surgeons. You should talk to your surgeon about his or her experience and recommendations, and then decide together what the best surgical plan will be for you.