Saturday February 24, 1996

Bone protein extract may replace bone grafts

Osteoinductive bone protein extract (BP), a substance that stimulates new bone growth, may one day replace bone grafts and the associated screws, pins, plates, and rods used for spinal fusion.

According to a study presented Thursday in scientific paper 73, Scott D. Boden, MD, made bone in primates by applying high doses of bovine-derived BP to the spines of rhesus monkeys. The induced bone growth successfully fused the spines, said Dr. Boden, associate professor of orthopaedic surgery, and director, Emory Spine Center, Emory University, Atlanta.

"Osteoinductive proteins result in a more reliable and biomechanically sound fusion than the autograft gold standard,"

Dr. Boden said. "The ability to make new bone could reduce the need for bone graft."

More than 169,000 spine fusions are performed each year in the United States.

In the study, researchers performed a lumbar intertransverse process spinal fusion on 24 adult rhesus monkeys to determine safety, efficacy, and the necessary dosage of BP in a nonhuman primate model.

Six monkeys received autogenous iliac crest as bone graft, and served as controls. The others were given various amounts of BP, combined with demineralized bone matrix (DBM) and collagen as the carrier. All monkeys tolerated the surgical procedure well, Dr. Boden said.

Doses of 6,000 g or 10,000 g BP initiated new bone growth and resulted in solid spine fusion in the rhesus monkey at 24 weeks.

Dr. Boden noted that the bone formed was better than the bone quality found in previous rabbit studies.

Monkeys given DBM without BP had very little new bone formation. No monkey that received less than 6,000 g of BP had a solid fusion.

The animals that were given 6,000 g or 10,000 g of BP and examined at 12 weeks had stiff, but not solid, fusions, Dr. Boden said. BP did not cause neurologic or other complications in any of the animals.

Among the two animals treated with bone graft (controls) that were examined at 24 weeks, only one monkey had a solid fusion; it was smaller, but similar in appearance, to the fusion in the 6,000 g and 10,000 g BP group. None of the control animals examined at 12 or 18 weeks had a solid fusion.

"The results of this study pushes us into a new era of biologic enhancement of spine fusion," Dr. Boden said.

In humans, a posterolateral intertransverse process fusion is the most common type of fusion performed in the lumbar spine.

"However, the rate of failure (nonunion) ranges from 5 to 35 percent," Dr. Boden said. "In addition, complications associated with bone graft harvest are seen in up to 30 percent of cases."

Co-authors of the study with Dr. Boden are Jeffrey H. Schimandle, MD, orthopaedic spine surgeon, Oklahoma City, Okla., and William C. Hutton, DSc, professor and director of orthopaedic research, Emory University School of Medicine, Atlanta.

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