Lumbar fusions can yield unpredictable results. With the problems that autograft presents-inconsistent quality, complications at the harvest site-there is simply no assurance of success. Not for surgeon, not for patients.
In introducing INFUSE® Bone Graft with the LT-CAGE® Lumbar Tapered Fusion Device, industry leader Medtronic has altered the landscape of spinal fusion technology. Studied under extensive clinical trials, INFUSE® Bone Graft and the LT-CAGE® Device consistently achieved rates of fusion and recovery equivalent to autograft.
Recombinant human bone morphogenetic protein (rhBMP) has long been recognized for its remarkable potential as a bone graft substitute. In fact, BMPs are the only known proteins capable of inducing new bone formation. And the first commercially available BMP ever to exhibit clinically proven osteoinductivity is the INFUSE® Bone Graft/LT-CAGE® Device.
BMPs in the Bone Formation Process
The osteoinductive activity of BMPs has exciting implications in lumbar spinal fusion procedures. BMPs initiate a complex multistage cascade of events in promoting in vivo bone formation. BMPs have been shown in both in vivo and in vitro studies to induce chemotaxis (stimulation of cell migration in response to a chemical signal), and cell proliferation. A significant amount of the research on BMPs has been performed to elucidate the effects of individual BMPs at a cellular level.
One of the first steps in bone formation is the migration of mesenchymal stem cells, osteoprogenitor cells, and osteoblasts to the area. These cells respond to chemical signals that are normally released in response to bone injury. rhBMP-2 can contribute to this influx of cells since it has been shown in vitro to have chemotactic properties for stromal osteoblasts and mature osteoblasts.
As the cells migrate into the area, they begin to proliferate. This proliferation can be enhanced by mitogenic factors present at the site of injury or graft site.
Creation of INFUSE® Bone Graft
The discovery of the natural osteoinductive factors in bone extracts was only the start of a long journey. The identification of the individual proteins responsible for the osteoinductive nature of bone extracts was a painstaking task. By using a series of extraction and purification steps, scientists were able to identify individual proteins that induce in vivo bone formation. The process was complicated by the fact that a time-consuming in vivo rat ectopic assay was necessary at each purification step to identify which fractions contained the components responsible for the osteoinductive activity. One of these osteoinductive proteins that were eventually identified was designated BMP-2. Once BMP-2 protein was identified and subsequently characterized, the next step was to identify the gene that encodes the human BMP-2 protein. The identification of the gene that codes for BMP-2 makes the production of a recombinant version of the protein possible.
Following its identification and isolation, the BMP-2 gene was inserted into the chromosome of a special type of mammalian production cell. This process is called recombination. These cells will then produce rhBMP-2, because the information provided in the BMP-2 gene is transcribed into the m-RNA and the m-RNA translated into proteins by the genetic and metabolic machinery of the mammalian production cell. The production cells are allowed to grow and multiply. The BMP-2 gene that was spliced into the production cell DNA is copied each time a production cell divides. Each new production cell is able to produce rhBMP-2 (the protein in INFUSE® Bone Graft).
Testing INFUSE® Bone Graft
Capping years of promising performance in preclinical studies, INFUSE® Bone Graft and the LT-CAGE® Device were tested in the most rigorous manner possible, in a prospective randomized large-scale clinical trial using an open surgical approach. Involving 279 patients and 16 investigative sites, the trial achieved its initial goal-proving that INFUSE® Bone Graft and the LT-CAGE® Device were just as effective as autogenous bone graft.
Other advantages surfaced as well. The INFUSE® Bone Graft/LT-CAGE® Device group lost less blood than autograft recipients. Operating times were shorter. And most notably, though statistically equivalent, rates of fusion were 94.5% in the INFUSE® group and 88.7% in the autograft group at 24 months.
Subjects had single-level, symptomatic degenerative disc disease.
The Study Findings
In preclinical studies, INFUSE® Bone Graft/LT-CAGE® Device proved safe and effective in lower species before higher order testing commenced.
Threaded Cages with Absorbable Collagen Sponge
The ultimate goal of interbody spine fusion is to achieve bony fusion across a disc space that has been distracted open to its normal height from a diseased compressed state. At this time, there are no BMP carriers that can sustain compressive loads associated with disc distraction and also degrade or remodel as fusion occurs. Therefore, in the development of INFUSE® Bone Graft for interbody spinal fusion applications, research was conducted ith the use of interbody constructs such as metallic cages. The interbody constructs posses internal spaces normally packed with autologous bone graft to achieve a fusion across the intervertebral space. The bone grafting material placed inside such interbody devices is not subjected to any significant loads or forces, eliminating the requirement that the carrier for BMP be load bearing under compressive forces.
The carrier for INFUSE® Bone Graft used in the interbody fusion studies was Type I bovine absorbable collagen sponge (ACS). This cohesive sponge is hydrated with INFUSE® Bone Graft solution at the time of surgery. The INFUSE® Bone Graft binds to the collagen sponge, which is then rolled and placed into the interbody device cavity.
It is important that you discuss the potential risks, complications, and benefits of INFUSE® Bone Graft/LT-CAGE® Lumbar Tapered Fusion Device with your doctor prior to receiving treatment, and that you rely on your physician’s judgment. Only your doctor can determine whether you are a suitable candidate for this treatment.