While spinal fusion presents many challenges for patients in the short term, the biggest problems usually arise several months to several years after surgery. What causes spinal fusion complications years later? Let’s take a look.
Adjacent Segment Degeneration: The Primary Cause of Spinal Fusion Complications Years Later
As you likely already know from your research, spinal fusion is the process of removing a vertebral motion segment from your spine—made up of a disc and its accompanying facet joints—and filling the gap with bone graft, screws, rods, and spacers. Over the course of several months, the newly inserted material fuses with the vertebrae above and below to make one solid mass of bone.
The absence of a vertebrae, and more specifically, the joint, changes the environment in which your spine operates. By stiffening a segment where there once was a joint, you create abnormal mechanical loads for the spine segments above and below the fusion. These abnormal loads add stress to the nearby facet joints and discs and make them work harder; as a result, they start to weaken. This condition is called adjacent segment degeneration.
Adjacent segment degeneration is by far the most critical problem with spinal fusion. Requiring the spine to work outside its normal range of motion can eventually lead to the development of other problems, in particular, spondylolisthesis or degenerative scoliosis.
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Spondylolisthesis refers to forward slippage of the spine—when a vertebral body slips forward on the bone directly beneath it. It is usually caused by natural wear and tear of the disc, when loss of disc height and ligament laxity impact the ability to stabilize the spine. Adjacent segment degeneration can bring on spondylolisthesis, where motions outside of the normal range at one level affect the stability of an adjacent level.
Adjacent segment degeneration may also sometimes bring on degenerative scoliosis. If the vertebrae adjacent to the fusion level—both the disc and facet joints—weaken enough as a result of excessive mechanical load, the spine may start to curve or rotate. (It’s possible for this to occur on two or even three adjacent levels.) The resulting spinal asymmetry may cause pain.
Disease Vs. Degeneration
Just about everyone who undergoes a fusion will, within five to eight years after surgery, show some x-ray evidence of abnormality in the spine, or degeneration. That doesn’t necessarily mean they’ll need additional surgery. The affected area might simply cause pain, aches, or a stiffness that’s manageable. But about 30 to 40 percent of fusion patients will develop adjacent segment disease, a condition that frequently requires additional surgical treatment.
The weakening and instability caused by adjacent segment degeneration may eventually bring on spinal stenosis. In response to the instability, the spine often attempts to restabilize itself by thickening the nearby ligaments and creating bone spurs (small projections that develop on the surface of a bone). These bone spurs and inflamed ligaments take up additional space and impinge on nearby nerves, compressing or “pinching” them, and causing spinal stenosis.
Ultimately, adjacent segment degeneration could lead to any of the following:
- Some people will develop pure spinal stenosis only.
- Some will develop spinal stenosis associated with spondylolisthesis.
- Some will develop spinal stenosis associated with degenerative scoliosis.
An important note about degeneration and spinal fusion: Most people naturally experience some degree of degeneration of the spine. However, this process typically starts later in life (around age 65) and progresses slowly. For spinal fusion patients, the degeneration process is accelerated. A process that normally takes 20 years might take five. On top of that, if you have a fusion when you’re 35 or 40, you’ve advanced that process many years.
An Alternative To Spinal Fusion
As more and more data are available on fusion outcomes, it’s clear that motion preservation (as opposed to fusion’s motion limitation) is an important factor in the health of your spine. (Studies like this one, for instance, show the reoperation rate for disc replacement patients is significantly lower than for fusion patients.) Motion prevents additional stress on adjacent vertebral levels, protecting them and slowing down their degeneration.
BalancedBack Total Joint Replacement is an alternative to fusion that keeps your spine moving naturally after surgery. It addresses all the most common causes of back and leg pain, but instead of removing a joint, the implant fully replaces the function of the joint. That means you’ll likely avoid premature degeneration of the adjacent joints—and the problems that degeneration causes—by not forcing them into potentially damaging postures, and preventing them from handling abnormal loads.
To learn more about BalancedBack Total Joint Replacement, visit our website.