Tissue Engineering Designed to Help Spine Surgery Patients
Developing natural or synthetic substances to replace the body's tissues, organs or functions is the goal of biomaterials research. In tissue engineering, synthetic compounds are used to augment patients' living tissue. For example, replacing bone grafts used in spinal fusion surgery with an engineered substance is under study at the biomaterials research laboratory at the Orthopaedic Rehabilitation and Engineering Center (OREC). OREC is a collaboration of the Medical College of Wisconsin and Marquette University.
A bone graft is a piece of bone transplanted to another part of the skeleton where it is needed to improve function or strengthen the structure of the area. Sometimes a bone graft is taken from a cadaver, but usually it is harvested from the patient for which it will be used. Aside from blood, bone is the most frequently transplanted tissue in humans. Bone grafts are typically harvested from the patient's iliac crest (top of the hip bone), ribs, or fibula in the lower leg. This can be quite painful and the complication rate can be high. Approximately 40% of spine fusion patients complain of pain at the harvest site for as long as five years after surgery.
Spinal fusion is a common procedure to alleviate certain types of back pain. Bone grafts or bone graft substitutes are used to replace the cartilage-like disc between the bony vertebrae. Over time, the graft and vertebrae form a continuous bony mass to stabilize the spine and relieve pressure on nerve roots, thus relieving pain.
Bone graft substitutes
Since 1992, the OREC biomaterials laboratory has been researching tissue-engineered bone graft substitutes. These include calcium phosphates, porous polylactic acid, tantalum and titanium. These biomaterials eliminate or reduce the need to harvest natural bone, thus avoiding an additional surgery, associated costs and certain surgical complications. A major contributing factor in the 30% failure rate in spinal fusion surgery is the poor performance and complications associated with natural bone. The goal is
to engineer bone graft substitutes that stimulate bone healing while performing well from a mechanical and biological standpoint.
Tissue-engineered bone graft substitutes have uses beyond spinal fusion surgery. They may be used to fill bone defects, such as when a fracture doesn't heal properly, or to replace bone lost to tumor surgery or trauma. They may be used in plastic surgery -- to reconstruct a chin, for example -- or in dental surgery to provide a bony bed for a dental implant. The application and surgical site help determine how a bone graft performs, if it
heals properly and offers the same durability as the original tissue. As a result, the OREC biomaterials laboratory has assembled an interdisciplinary research team that includes engineers, orthopaedic surgeons and dentists.
Reducing the rejection rate for bone grafts
One of the team's findings has led to additional funding from the National Arthritis Foundation. Bone morphogenetic proteins (BMPs) regulate bone healing. When added to biomaterials, BMPs change the way the body reacts to those materials. The combination of BMPs and biomaterials forms a potent bone graft substitute. BMPs speed up bony healing, and also appear to overcome the immune system's response to donor bone, which sometimes results in the body "rejecting" the graft. A co-investigator on the arthritis study is Raj Rao, MD, Assistant Professor of Orthopaedic Surgery at the Medical College.
The OREC biomaterials laboratory has conducted animal experiments to determine whether or not these materials are safe and effective. Some of these materials are in human clinical trials now, but none have yet been approved by the US Food & Drug Administration. It is hoped that additional research may one day render bone grafts obsolete. The OREC team has published a variety of studies on the topic, including "Practical Illustrations in Tissue Engineering: Surgical Considerations Relevant to the Implantation of Osteoinductive Devices," in Tissue Engineering, August, 2000.
The OREC biomaterials laboratory has also been involved in studies of various spinal fixation technologies, providing analysis for the FDA.
Jeffrey M. Toth, PhD
Associate Professor of Orthopaedic Surgery
Medical College of Wisconsin
Associate Adjunct Professor of Biomaterials (Dentistry)
Associate Adjunct Professor of Biomedical Engineering
Associate Adjunct Professor of Mechanical and Industrial Engineering
Marquette University
Article Created: 2001-02-13
Article Updated: 2001-02-13
MCW Health News presents up-to-date information on patient care and medical research by the physicians of the Medical College of Wisconsin.
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