Adjacent segment disease (ASD), the irreversibility of fusion, and why SCS may be an alternative to consider.
Fusion is an effective treatment, but it cannot be undone, so the decision deserves careful thought.
What You'll Learn
- What adjacent segment disease (ASD) is
- How common it is
- Why it happens
- The timeline of progression
- What symptoms to watch for
- How to reduce the risk
- What to do if ASD develops
- Understanding the irreversibility of fusion
- What to consider before deciding on fusion
Years after lumbar fusion surgery, some patients develop new pain or nerve compression at the levels immediately above or below the fused segment. This is called adjacent segment disease, or ASD for short.
Picture a three-drawer dresser with the middle drawer nailed shut. The top and bottom drawers now get pulled open and pushed closed more than before, so over time their rails and frames wear out faster.
The numbers vary across studies, but large studies show the following:
In short:
Adjacent segment problems build up over years, not right after surgery. The more levels that are fused, the higher the risk of another operation.
| Time / Group | What Happens | Source |
|---|---|---|
| Long term (pooled) | Imaging changes in ~27%; symptoms in ~9% | Xia XP et al., Spine 2013 (meta-analysis of 94 studies) |
| 5 years | ~14% had surgery at a neighboring level | Sears WR et al., Spine J 2011 (1,000 fusions) |
| 10 years | ~22% had surgery at a neighboring level | Same |
| 10 years, by levels fused | 1 level 16% · 2 levels 31% · 3–4 levels 40% | Same |
| Japan | 9% reoperated over a mean of 8.3 years | Okuda S et al., Global Spine J 2018 (1,000 patients) |
Imaging changes do not equal symptoms: About 27% show changes on scans, but only about 9% have symptoms. The risk does rise steadily over time, and a meaningful share of patients eventually need surgery.
When the fused segment stops moving, the neighboring levels must bend and extend more to compensate. Years of this extra motion accelerates wear on the discs and can lead to slippage.
During fusion, the bone and ligaments at adjacent levels may be partially removed. This can make those levels less stable and more susceptible to ASD.
Research shows:
(Simonetta B et al., Spine 2025)
If the screws used for fixation encroach on the facet joint at the neighboring level, the stress on that joint increases, raising the risk of ASD.
The angle at which the vertebrae are fused has a major impact on neighboring levels. The lower back naturally maintains a forward curve (lordosis) when you stand. Preserving this natural curve during fusion is ideal. If the curve is not maintained, the adjacent levels bear more stress and ASD becomes more likely.
Limiting fusion to the minimum necessary number of levels is important. The five lumbar vertebrae move a lot in daily life. Each level that is fused leaves fewer levels to share the work, so each remaining level carries more.
Many people with adjacent segment changes never develop symptoms. When symptoms do appear, they may include:
In other words, symptoms similar to those you had before your original surgery may come back.
After surgery:
These help stabilize your entire spine, reducing the extra burden on neighboring levels.
ASD typically develops over several years, not immediately after surgery. So it is important to:
If you have no symptoms, no treatment is needed. Even if imaging shows changes, that alone is not a reason for surgery.
From the guideline commentary:
Whether or not implants were used does not significantly affect the rate of adjacent segment changes. So ASD is not only a fusion problem; it can also occur after decompression alone. Patients who already have degeneration at adjacent levels before surgery tend to have worse outcomes, and those with advanced degeneration have higher rates of new leg symptoms and reoperation.
A prospective database analysis found that the reoperation rate at up to 5 years was approximately 14%, regardless of whether fusion was performed.
Fusion is an effective treatment, but it is a decision you cannot undo.
| Aspect | What It Means |
|---|---|
| Permanent fixation | Once vertebrae are fused, they will never move again |
| Stress redistribution | Permanent extra stress is placed on the levels above and below |
| Fewer future options | If pain continues after fusion, treatment options become more limited |
| Diminishing returns with reoperation | Each subsequent surgery tends to be less effective |
What you should know:
Fusion done for the right reasons is a highly effective treatment. Still, keep in mind that:
Talk it through with your surgeon, and go ahead only when you are fully comfortable with the decision.
There are situations where surgery for nerve decompression or spinal reconstruction is clearly necessary:
In these cases, surgery takes priority.
If none of the above apply and your main problem is pain, it may be worth considering spinal cord stimulation (SCS) before committing to an irreversible fusion.
SCS has these advantages:
If fusion has been recommended, ask your surgeon: "Why isn't decompression alone sufficient?" and "Is fusion truly necessary given my condition?" Then also ask whether SCS might be an option worth exploring.
Learn about spinal cord stimulation (SCS)
If fusion surgery is being recommended, discuss these questions:
"Why isn't decompression alone sufficient?"
"Is the number of levels being fused the minimum necessary?"
"What is my personal risk for adjacent segment disease?"
"Can this be done with minimally invasive techniques (MIS)?"
"Could SCS be an alternative to fusion in my case?"
"If ASD develops in the future, what treatment options would I have?"
| Key Point | Details |
|---|---|
| What ASD is | New problems at the levels above or below the fused segment due to increased stress |
| How common | Imaging changes in about 1 in 4; symptoms in about 1 in 12; another operation in about 1 in 5 by 10 years |
| Main causes | Increased mechanical stress, surgical impact, number of fused levels, spinal alignment |
| Prevention | Minimize fused levels, use MIS, maintain lordosis, core strengthening |
| Progression | Develops over years; regular follow-up is essential |
| Irreversibility | Once fused, it cannot be undone, so the first decision matters most |
| Consider SCS | If pain is the main symptom, spinal cord stimulation (SCS), which can be removed if it does not suit you, may be worth discussing before fusion |
→ Spinal Cord Stimulation (SCS): a reversible alternative to consider before committing to fusion
→ Treatment Overview: all your treatment options in one place
→ SCS Detailed Guide: devices, surgery, and life with SCS explained in depth
→ Detailed Treatment Comparison: long-term risks and outcomes of fusion and SCS
This page provides medically accurate information, but it is not a substitute for professional medical advice. Please consult your doctor for diagnosis and treatment tailored to your individual situation.