Spinal Fusion, Dynamic Fusion, and Disc Replacement
Any number of conditions may destabilize the spine: arthritis, removal of intervertebral disc, or osteoporosis. Regardless, if the spine becomes too unstable, conditions and pain may worsen. The goal of this type of surgery is to stabilize the vertebrae.
If you are contemplating surgery, there's no better time to get in physical condition. The stronger your back and abdominal muscles pre-surgery, the easier rehab will be.
You might hold the common misconception that fusions are undesirable and limit mobility. And it's true that fusion will limit some mobility when you compare it to someone who has no spine problems. But this procedure can be a saving grace, especially when your joints have totally deteriorated and bone spurs obstruct nerve passages.
Fusion is actually what the body does naturally in response to some traumatic conditions. Surgery moves the process along more quickly and also benefits patients by releasing trapped nerves. Some people may find their mobility is actually better after fusion because they are no longer in pain. The painful segment that kept them from moving at all is now immobile, leaving the rest of the spine free to bend and twist.
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Traditional fusion can create excess pressure on surrounding vertebrae, which can lead to disc problems elsewhere in the spine. This is called adjacent segment disease. It is one reason surgeons are reluctant to do multilevel fusions. The longer a fused segment, the more pressure on neighboring levels, and with time there may be a need for further surgery.
In fusion, the goal is to immobilize the painful segment and bridge the two vertebrae with bone. First, surgeons stabilize the spine with titanium or stainless steel rods and screws. This acts as an internal brace. Bone graft is then inserted to grow between the two vertebrae. Bone graft material is obtained from the bony decompression, the patient's own hip (although this is rarely done these days), a donor, or a genetically engineered source. It takes about six months for the spinal bones to fuse together.
Sometimes decompression may make the spine unstable but a fusion is not needed. Dynamic stabilization reinforces the spine to allow more natural motion than a fusion. This is still an investigational procedure but it may reduce the risk of adjacent segment disease.
One benefit of dynamic stabilization is that it provides support without fusion, so ideally little motion is lost. The goal is to lessen the chance of the next vertebral segment from the spine wearing out as quickly because you can distribute forces. The downsides are that this procedure is not recognized as a standard of care, so most insur ance companies do not cover it.
Only a few surgeons in the U.S. perform dynamic stabilization. There is some concern that the hardware may loosen over time because there is motion there. Once a fusion has healed, there is no motion, so hardware does not loosen. Also, dynamic stabilization allows motion at the treated level, which may cause pain. In some cases, a fusion eliminates the painful motion and may be a better option.
When a disc has to be entirely removed, something has to replace it or else the vertebrae will sit on top of one another. In cases of severe disc degeneration, the disc is practically gone anyway. Any movement of the spine will cause bone-on-bone friction. So the patient's choice is either fusion or disc replacement.
Developing an artificial disc has been in the works for decades. Creating a device that works for a diverse population and can replicate the natural movements allowed by real discs is challenging, to say least, but progress has been made. In 2004, the CHARITÈ Artificial Disc became the first artificial disc to be approved by the U.S. Food and Drug Administration as a surgical treatment for patients suffering with single-level degenerative disc disease in the lower back.
Unfortunately, artificial discs, particularly in the lumbar spine, perform no better than fusion in long-term studies. In fact, they have been associated with more complications, because they allow movement and are subject to mechanical failure. Because of this, few insurance companies in the U.S. cover this procedure.
Although not right for everyone or every condition, artificial discs do help mimic the movement of a real intervertebral disc. Two metal plates with a plastic core replace the natural disc and enable the spine to move.
Jason Highsmith, MD is a practicing neurosurgeon in Charleston, NC and the author of The Complete Idiot's Guide to Back Pain. Click here for more information about the book.