In spinal fusion surgery, the bone graft is the material that is used to form the bridge between two vertebral segments in the spine to obtain the fusion. Bone grafts can be divided into three main categories based on where they are obtained.
- Autograft bone graft is the term used when the patient’s own bone is used to for the bone graft in the spine fusion. The most common donor area is the iliac crest, which is located in the patient’s pelvis. Local bone from the area of surgery such as lamina and spinous process bone are technically considered to be autograft as well. However, the iliac crest autograft is considered to be the gold standard and is most often used as bone graft in a spine fusion. However, it does carry the risk of donor site morbidity, or unwanted aftereffects such as postoperative pain at the donor site (the pelvic rim).
- Allograft bone graft is bone obtained from cadavers, and comes in many shapes and forms for use in a spine fusion. There are different techniques of sterilization as well as different storage techniques for allograft bone, such as fresh frozen or freeze-dried. At present, this is the most commonly used alternative to autograft bone, and is most commonly used as a bone graft supplement (to the patient’s own bone) in the back of the spine in adult patients. It may also be used in a fusion procedure to treat scoliosis in adolescent patients.
- Bone graft substitutes are products that either assist or replace the need for autograft or allograft bone in a spine fusion. For example, tricalcium phosphate acts as a structural lattice for bone formation. Other bone graft substitutes such as demineralized bone matrix, are used as graft extenders and can be used to mix with allograft and increase fusion rates.
Bone Morphogenetic Protein (BMP) is a commercially available protein, which has been shown (when placed in fusion cages for interbody fusion) to have the same rate of fusion as the iliac crest allograft without the potential for donor site morbidity (unwanted aftereffects, such as postoperative pain). However, at present BMP is extremely expensive, and this product is only approved by the FDA for an anterior approach (when the fusion is done from the front).
The addition of the patient’s bone marrow aspirate (obtained thru a needle rather than an additional incision) to allograft, has promise of obtaining better fusion rates than allograft alone, and may be more cost effective than other bone graft substitute options.
The choice of which type of bone graft to use is largely dependent upon where the fusion is done in the spine (in the cervical, thoracic, or lumbar spine), and the surgical approach to the fusion (anterior or posterior). A number of other factors also play a role in the decision, such as whether or not the patient smokes or has other risk factors that may inhibit a successful fusion.
This article has reviewed many of the different options available to achieve a spine fusion. All of the different approaches with spine fusion have certain risks and complications. One common risk among all types of spine fusion that is important to keep in mind is the risk of clinical failure, which means that despite achieving a successful fusion the patient’s pain is not alleviated.