Spinal fusion is a common surgery performed to alleviate pain caused by spinal instability resulting from a condition such as degenerative disc disease or spondylolisthesis (the forward slipping of a vertebra). It’s an invasive procedure that generally requires a bone graft and hardware to make one or more spinal segments rigid; over time, the bone graft fuses the two (or more) vertebrae together.
Spinal fusion comes with the risks of all major surgeries – infection, bleeding, scar tissue formation, etc. But it also comes with a unique risk: adjacent segment disease (ASD). This occurs when the disc above the site of fusion begins to wear at an accelerated rate because the disc that was below it is no longer there to absorb shock. This can result in pain, nerve compression and even the need for another surgery.
Studies are mixed on just how prevalent ASD is, and even whether or not it is really a problem. While some studies report notable rates of symptomatic ASD post-fusion, a recent review of 4 trials with long-term follow-ups ranging from nine to 17 years found that, while patients who had fusions showed greater degeneration of the spinal disc above the site of fusion than did patients who hadn’t had the surgery, their self-reported pain and disability levels were not negatively impacted by this. See more on this at www.ncbi.nlm.nih.gov.
Still, ASD is worth considering as a spinal fusion risk, since it could spell trouble later on. This is just one reason, along with cost and invasiveness, that patients are often eager for alternative procedures to alleviate the pain caused by spinal instability.
Dynamic lumbar stabilization with the Dynesys system may be that alternative, although more research is needed. This system uses screws, cords and spacers to stabilize spinal segments while retaining range of motion. Spacers are used to set the vertebrae at a natural distance from one another, and the cords facilitate shock absorption and movement. What is more, this method is less invasive than open fusion.
Theoretically, the Dynesys method should prevent ASD, since it provides stability while avoiding the creation a completely rigid spinal segment. However, few studies have compared ASD rates for dynamic stabilization with those for fusion. You can find a 2013 research round-up at omicsgroup.org. This round-up suggests comparable results for dynamic stabilization and fusion in the few studies that have been done, but calls for more research.
Some research has been done in 2014 as well. While one small study of 37 patients, found at www.ncbi.nlm.nih.gov, showed no significant changes in adjacent discs for dynamic fusion between nine and 36 months, another one, at www.ncbi.nlm.nih.gov, found that three out of 30 patients (10%) developed symptomatic ASD within two years of dynamic stabilization surgery.
As of now, dynamic stabilization holds promise as a spinal fusion alternative, but there is no smoking gun in its favor. Once more research is done into its impact on adjacent discs and how it compares with spinal fusion in terms of effectiveness, we will know more about its potential to serve as an alternative.