By Ori Twersky

WASHINGTON (Reuters Health) – An expert advisory panel to the US Food and Drug Administration (FDA) on Thursday unanimously backed the approval of a Medtronic Inc. genetically engineered bone graft, designed to offer patients with degenerative disc disease an alternative to harvesting their own bone.

Degenerative disc disease is a common disorder of the lower spine believed to be a major cause of lower back pain. In severe cases, the condition generally is treated using a spinal cage implant to stabilize the spine combined with a bone graft taken from the hip region to spur new bone growth. An estimated 150,000 such procedures are performed each year in the US, according to Medtronic figures.

The FDA's Orthopedics and Rehabilitation Devices Advisory Panel voted to recommend that the agency approve Medtronic Inc.'s InFuse Bone Graft, a genetically engineered version of the Bone Morphogenetic Protein (BMP-2). The protein, first identified in 1980s by scientists at American Home Products Inc., has been shown to induce bone growth in more than 30 years of study.

Medtronic Inc. subsequently licensed the protein from the Genetics Institute unit of American Home Products.

Approval of the bone substitute would mean that many patients undergoing spinal fusion surgery for degenerative disc disease will no longer need to also undergo surgery to harvest bone from their hip, when opting to use Medtronic's LT-Cage Lumbar Tapered Fusion Device.

The LT-Cage Lumbar Tapered Fusion Device was designed to offer a less-invasive alternative for placing the spinal cage implant in the spine. The device is implanted laparoscopically, or through an open frontal incision. Medtronic commercially released the device last February. At present, the device is implanted with harvested bone.

The panel's decision to approve the substitute bone graft insert was based upon the evaluation of a two-year long clinical study, in which the genetically engineered substitute was compared with harvested bone. A total of 279 patients participated in the study, the results of which were first released at the November meeting of the North American Spine Society in Seattle, Washington.

At 24 months, the investigators said that the In-Fuse treated group displayed a fusion success rate of about 94.5% compared with 88.7% for the control group. The investigators said that patients also experienced a more than 50% improvement in back pain based on a patient questionnaire, which measured the incidence and intensity of pain.

In contrast, the investigators said that all of patients undergoing the secondary surgery to harvest bone from the hip region suffered from subsequent hip pain following the surgery, and almost a third were still experiencing pain up to two years later.

The FDA's expert advisors did not contest that data.

But the panel did express reservations regarding the bone substitute's potential long-term side effects. Among those was the bone growth substitute's theoretical potential to induce the growth of cancerous cells and stimulate an immune response in pregnant women, causing possible birth defects. The panel also expressed concern about the possible off-label use of the bone growth promoter for unapproved purposes.

In animal studies, there was no evidence that the BMP-2 substitute would induce the growth of cancerous cells or cause birth defects. The panel's safety concerns were based on the lack of longer-term data.

The FDA expressed similar concerns in documents released prior to the meeting. The FDA investigators said that while they believed the bone substitute could be approved, post-marketing studies would be needed to evaluate the protein's potential long-term side effects.

As a result, the FDA and Medtronic already had agreed to conduct additional non-clinical studies on the substitute's potential to stimulate the growth of cancerous cells if the product was approved.

At question before the panel was whether it should also recommend that the FDA require Medtronic to establish a patient registry, develop additional animal models and take other steps to prevent the potential abuse of the bone growth promoter. At question was also whether these studies should be conducted prior to approval.

Following discussion, the panel recommended that the FDA should require at least two additional animal studies to determine the protein's effect on cancerous cells and whether it can result in the formation of cancerous cells. The panel also recommended that the FDA should require an animal study to model the potential effect on pregnant women.

However, the panel determined that these studies could be conducted post-approval.

In an interview following the vote, President of Medtronic's Sofamor Danek division Michael F. DeMane told Reuters Health that the company now believes the bone substitute will become the standard of care. He said that surgeons have been awaiting this development for about 30 years.

"We have taken a significant step toward changing patient care," DeMane said.

He said that the firm expects to launch the InFuse Bone Graft in July.

In Thursday trading on the New York Stock Exchange, shares of the Minneapolis, Minnesota-based concern closed up 0.46 at 48.74. The panel's decision came after the close of the market.