There are four reasons for patients to undergo a bone graft

Main Category: Bones / Orthopedics
Article Date: 19 Apr 2004 - 0:00 PDT

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According to George F Muschler, MD, there are four reasons for patients to undergo a bone graft. "The largest area where a bone graft is performed is for arthrodesis, which involves fusing two bones together because the joint space in between those bones causes pain. By elim-inating the joint and the motion, the pain is relieved. In fact, about half of all bone grafts involve arthrodesis procedures in the spine, also referred to as spinal fusions. Other grafting procedures relate to the treatment of fractures, defects or skeletal deformities, or instability problems involving joints in the upper and lower extremities."

An estimated 500,000 bone graft procedures are performed each year in the United States and one million worldwide.

Defects in the skeleton are gaps where bone is missing, which can be a result of infection, trauma, or removal of tumors. Bone grafting can be performed early after a fracture occurs if it is at risk of not healing and after a fracture non-union develops in which a fracture fails to heal after conventional treatments have been attempted.

The purpose of all traditional procedures for bone grafting is to stimulate new bone formation. Dr. Muschler says, "the goal is to grow bone where it is needed. Traditional bone grafting involves borrowing bone tissue from one location and transplanting it to another location. The problem with conventional techniques is that surgeons must go to a normal tissue site.

"The most common method is to remove chunks of bone from the hip area or the iliac crest, the part of the pelvis where abdominal muscles attach."

When the bone is transplanted, new bone formation occurs about 90% to 95% of the time, but Dr. Muschler says the standard techniques have been associated with significantly poor morbidity.

"Between 8% and 20% of patients have persistent pain or discomfort at the site where bone was taken. In addition, patients experience pain, blood loss, and risk of infection, fracture, and neurologic injury during the time when bone is taken. The sum total of the morbidity associated with borrowing bone is the biggest drawback in traditional procedures."

Currently, there are no oral medications available to improve bone healing, but Dr. Muschler believes there are opportunities to develop other treatments to effectively promote bone healing.

"Research has suggested injections of parathryroid hormone (pTH) after a fracture occurs might improve the amount of bone formation and the success of bone healing. There are also implantable biological agents that can be applied at the site where bone healing is needed and research indicates that they can be beneficial to the patient."

Dr. Muschler says that several examples of these agents come from the 15 proteins that make up the family of bone morphogenetic proteins (BMPs), which exist in the human genome and transform growth factor (TGF) beta.

When some BMPs are implanted into fat, muscle, or bone site, they can activate responding ion of cells and induce them to subsequently create new bone tissue.

Some of these molecules can also stimulate a fibrous tissue response, cartilage formation, or bone formation where they are implanted.

"There are two BMP products currently approved by the FDA, albeit for very limited applications. Recombinant human bone morphogenetic protein-2 (rhBMP-2) (InFUSE, Medtronic) was approved for use in anterior interbody fusion. The protein provides predictable bone healing, even without the transplantation itself, as long as the tissue around the site is healthy. The second product is osteogenic protein-1 (OP-1, Stryker Biotech), which is also known as bone morphogenetic protein-7 (BMP-7). OP-1 is approved to treat non-unions in long bones where autograft is unfeasible and alternative treatments have failed."

From: Physicians Weekly
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