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I'm going to a university hospital where there is a world famous neurosurgeon who does lumbar fusions. I heard they use an off-label glue or something to hold it all together. I won't have to donate bone to myself with this new method. What can you tell me about this before I get there?
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Surgeons continue to look for ways to fuse the lumbar spine with the best results and fewest problems. One of the biggest problems with spinal fusion is the need for bone graft material. Bone chips taken from the patient's hip (iliac crest) work but often leave undesirable pain, infection, and swelling at the donor site. New biologic agents might be able to speed up the fusion process and do it without the use of bone graft material.
One of those biologic agents is rhBMP-2 or recombinant human bone morphogenetic protein. rhBMP-2 is a growth factor that can be used to stimulate bone growth. Right now, rhBMP-2 has been approved by the FDA for use in spinal fusions. In its liquid form, it is placed on a sponge (called the carrier). The sponge is put inside a tiny cage that is then implanted between the two vertebrae. The disc that normally sits between the two vertebral bones has been removed first in a procedure called a discectomy. The discectomy is done to remove the damaged disc material and make room for the intervertebral cage.
In its off-label use, the procedure just described with the sponge carrier inside the cage is still used. But in addition, the surgeon puts some rhBMP-2 in the space left by the discectomy before inserting the cage (that's the off-label use). The rhBMP is pushed up against what's left of the disc lining (the annulus fibrosis), then the cage is set behind it. This pushes the cage back a bit from where it would normally rest without the additional rhBMP-2. The cage ends up being flush or even with the back wall of the vertebral bone.
There have been some problems with this approach. There has been some leakage of the rhBMP outside of the cage and inside the spinal canal. As a result, bone has formed where it doesn't belong. In a few cases, bone has formed inside the spinal canal and wrapped itself around the spinal nerve root as it leaves the spinal canal. Serious neurologic problems can develop as a result of this complication.
That's why efforts are being made to modify the procedure and see if these (rare) problems can be resolved. Those who are using rhBMP-2 in an off-label way as described here now build in protective layers using crushed bone and a layer of fibrin glue. A layer of bone is placed between the rhBMP-2 and the annular covering at the front of the empty disc space. Then the rhBMP-2 goes in and then another protective layer of bone. Next goes the cage filled with the rhBMP-2 carrier. The final layer (a special fibrin glue) is placed behind the cage. They also pay close attention to where the cage is placed. Putting it as far forward as possible (and as far away from the nerve tissue) may help reduce the problem of neural compression.
This may not be exactly what your neurosurgeon does or has planned. The procedure will probably be explained to you during the pre-operative visit. Keeping this information in mind, you'll be able to ask questions and understand first hand what will be done during your procedure.
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