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Questions Raised About Bone Substitute for Lumbar Spine Fusion
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Posted on: 08/24/2011
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Would you think zero complications in 13 studies of 780 patients receiving a new bone substitute product called rh-BMP-2 (BMP) is too good to be true? Those were the findings reported in early industry-sponsored trials. It was first used in 2002, so now we have almost 10 years of data to consider.
BMP stands for bone morphogenetic protein. Rh-BMP-2 is a protein that helps bone heal. BMP reportedly helps speed up the recovery rate after spinal fusion. BMP is designed to promote bone formation by setting up an inflammatory reaction. This type of enhancer was developed to avoid problems that occur with traditional bone grafting. But no adverse reactions or events raised a few eyebrows at the time of the first published reports.
And here again in this systematic review, surgeons from several different spine centers are pointing out some problems with the original research. By going back over all the published reports (industry-sponsored, FDA-data, and privately-sponsored publications), they were able to see there is a much higher risk of complications directly related to the rhBMP-2 product than was originally reported.
What types of problems did patients experience? And why didn't these BMP-related adverse events show up in any of the original studies? rh-BMP-2 has been used now in lumbar spine fusions as well as cervical spine (neck) fusions.
This review focuses on both cervical (neck) and lumbar (low back) spine procedures. There are four separate methods for which rh-BMP-2 was used: 1) anterior interbody lumbar fusion, 2) posterior lumbar interbody fusion, 3) posterolateral fusion, and 4) anterior cervical discectomy and interbody fusion (ACDF).
As you can see by the names, the differences relate to the location, direction, and placement of the fusion. The first three are methods for lumbar spine (low back) fusion. The fourth one is a cervical spine (neck) fusion. Anterior means the fusion is done from the front of the spine. A posterior fusion is performed from the back of the spine. And a posterolateral fusion comes in at an angle with fusion along the side and back of the vertebrae.
Each of these procedures has its own benefits and risks. This systematic review focused just on risks associated with the fusion material (the rh-BMP-2 bone substitute). By taking a look back at the data collected, the authors of this review found that there was really a complication rate anywhere from 10 to 50 per cent reported.
For the one cervical spine procedure (anterior cervical discectomy and interbody fusion), the risk of complications with rh-BMP-2 as the fusion material was 40 per cent higher than for patients who did not get BMP.
What are these complications? Shifting of the implant, sinking down called subsidence, infection, extra bone formation, osteolysis (breakdown of bone) and increased back and leg pain top the list. Other problems such as the growth of cancerous tumors, bladder retention of urine, and retrograde ejaculation have also been reported.
Men are at risk for damage to the nerves controlling penis erection and ejaculation. With retrograde ejaculation, semen goes backwards and into the bladder instead of forward and out the penis. Not everyone recovers from this problem. In fact, only about one-third regain complete sexual function.
Retrograde ejaculation may not be life-threatening, but it is a very serious problem for those who develop this complication. Loss of sexual function and sterility (inability to have children) can adversely affect mental and emotional health as well as quality of life.
With the neck fusion, there were some life-threatening complications. Swelling of the neck and throat put pressure on the patient's airway making it difficult to swallow, talk, and even breathe.
And the development of cancer is potentially life-threatening. As a product designed to stimulate bone growth, BMP may actually trigger cell growth resulting in cancer. The complication is for sure -- the biologic mechanism by which it happens remains uncertain.
In general, overall function and outcome measures were consistently lower for patients who received rh-BMP-2 compared with patients in control groups (those who did not have BMP as part of the fusion procedure). How do we explain the discrepancy between zero industry-reported complications and a 50 per cent complication rate published in other studies?
Study design, funding of studies by the company making the product, bias by researchers employed by the companies making the bone substitute, and conflict of interest are named as potential sources of this reporting style.
Anyone being rewarded financially by the success of their own product may have a tendency to be overly enthusiastic by results and overlook potential problems. In some industry funded studies, there was simply no mention or discussion at all of problems.
In summary, this systematic review represents almost 10-years worth of research. The authors once again raise questions about the safety of this fairly new biologic bone substitute product called rh-BMP-2.
Data from private researchers, reports submitted to the FDA, and studies sponsored by groups like the Scoliosis Research Society are now available. Their results clearly demonstrate a much higher complication rate linked with the use of rh-BMP-2 than was originally reported by early studies funded by companies developing this product.
Further studies are needed to address these (and other) concerns. For example, the link to cancer is a significant concern. Perhaps the problem can be solved by simply regulating the dose of the BMP product.
Finding the lowest amount that can be used to get the maximum benefit may be an important research goal. Long-term studies to see the effects using BMP compared with traditional bone grafting techniques is another area where study is needed.
And finally, all future studies must be reviewed carefully. Funding sources, study design, and methods of analyzing and reporting the data should be examined in order to determine the true benefits, adverse effects, and safety of rh-BMP-2 in spinal fusion.
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References:
Eugene J. Carragee, MD, et al. A Critical Review of Recombinant Human Bone Morphogenetic Protein-2 Trials in Spinal Surgery: Emerging Safety Concerns and Lessons Learned. In The Spine Journal. June 2011. Vol. 11. No. 6. Pp. 471-491.
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