In recent years, one of the exciting developments in the spine field has been the emergence of the use of biologic materials in spine surgery. This is an important part of spinal surgeries, and has been a recent topic of great controversy in regards to studies, evidence, and potential complications. One of the leaders in this field is Jeffrey C. Wang, MD. Dr. Wang is based at the University of Southern California (USC) and, in addition to his busy practice, he runs a basic science laboratory where he is constantly developing and testing new methods to treat spinal disorders. Recently, Dr. Wang gave SpineUniverse some of his time to help us better understand new biologic materials and the impact they will have on the future of spine surgery.

SpineUniverse: Dr. Wang, to begin, what does the term biologic material mean?
Dr. Wang: A biologic material is typically used to describe a substance that actively alters the surrounding environment and effects a change in the environment that progresses through an active, biological process. In other words, the effects can be seen through increased cellular activity, growth, and differentiation.

For example, pedicle screws and rods are often used in a spine fusion procedure to provide spinal stabilization, which promotes fusion healing. However, those pieces of metal (eg, pedicle screws) do not typically stimulate or activate cellular growth or alter cellular function; the metal is an inert material. On the other hand, a biologic material or bone graft that attracts more cells to the fusion site can actively increase bone formation and stimulate spinal fusion.

SpineUniverse: Are any biologics currently being used in spine surgery?
Dr. Wang: The use of biologics in spine surgery has always been an important component in any spinal fusion surgery. The biologic material or bone graft is a critical element in the fusion healing process. A surgeon cannot perform spinal fusion without considering the biological healing of the actual fusion; the use of a biologic material or agent to promote the fusion process.

In the past, there were few options—primarily using the patient's own bone (ie, autograft). The surgeon removed bone from one area of the patient's body (eg, iliac crest/hip) and used the bone as graft implanted into the spine for fusion. This is described as an autograft.

SpineUniverse: If autograft is available, then why develop other biologics for the spine?
Dr. Wang: Many surgeons still use autograft as their primary bone graft of choice. However, the use of autograft often requires a separate surgical incision and removal of bone from an area of the body outside the spine.

Essentially, this is an additional surgical procedure with a new incision, and potential for a significant rate of morbidity. Removal of bone outside the spine has potential complications that may include:

• Pain
• Infection
• Palpable defect where bone was removed
• Fracture of the weakened bone.

Furthermore, availability of autograft is limited. Typically, bone can only be removed from a area once. This can present a problem for patients who require additional surgery. In children, the areas available for autograft are small, and there may not be enough bone to successfully heal the fusion. These scenarios represents some of the reasons why other types of biologic materials are needed.

SpineUniverse: If my spine surgeon plans to use autograft or allograft during my surgery, should I be concerned?
Dr. Wang: Patients should not be too concerned if their surgeon plans to use autograft or allograft in their spine surgery. Autograft bone is considered the "gold standard" and is the most commonly used graft for spinal fusion. As we study the results of biologic materials and other graft replacements, the use of autograft will most likely diminish, being replaced by other bone graft products that are used as substitutes.

Allograft bone, especially in the cervical spine, works well and the risk of problems specific to the graft material is quite low. There are a number of allograft-derived bone graft extenders that are often used for bone graft replacement. These are commonly used in all areas of the spine. I would caution, although there are a large number of bone graft materials available for use, and they appear to be safe—there is limited evidence, studies, and data demonstrating they are effective.

I am always pushing surgeons to ask for more definitive data on the effectiveness of bone graft products. I personally feel that this is an area that requiring many more studies and proven effectiveness.