Adjacent segment disease (ASD) is the breakdown of spinal discs and joints next to a previously fused section of spine. After spinal fusion surgery locks two or more vertebrae together, the segments directly above and below the fusion absorb extra stress, and over time this accelerated wear can cause new disc herniations, spinal stenosis, or arthritis in those neighboring joints. The condition develops at a fairly steady rate of about 2.5% per year, meaning roughly 1 in 5 patients will need a second surgery within 10 years of their original fusion.
Why Fusion Creates Problems Nearby
A healthy spine distributes movement and load across many segments. When fusion eliminates motion at one or more levels, the segments that remain mobile have to pick up the slack. They bend more, absorb more force with every step or twist, and their discs and facet joints wear down faster than they otherwise would.
The effect scales with the size of the fusion. After a single-level fusion, about 16% of patients require surgery on an adjacent segment within 10 years. That number climbs to 31% after two-level fusions and 40% after fusions spanning three or four levels. The longer the rigid section, the greater the mechanical burden on whatever’s left unfused.
There is an ongoing debate about how much of this degeneration is caused by the fusion itself versus the natural aging of a spine that was already prone to disc disease. Many patients who need fusion already have some degree of wear at neighboring levels before surgery ever happens. The honest answer is that both factors likely contribute, and separating them cleanly has proven difficult.
Who Is Most at Risk
Pre-existing wear at neighboring segments is the strongest patient-related risk factor. Specifically, facet joint degeneration (the small joints at the back of each vertebra) at the level next to the planned fusion has been identified as a statistically significant predictor. Even a modest amount of facet wear before surgery raises the odds.
Age, somewhat surprisingly, has not held up as a consistent risk factor in recent research. Earlier studies suggested patients over 55 were at higher risk, but multiple newer analyses found no meaningful age difference between people who developed ASD and those who didn’t. Other factors that have been studied but remain less clearly established include body weight, smoking, pre-existing disc bulging, and subtle alignment issues like a slight forward slip of one vertebra over another.
The surgical variables matter as much as the patient variables. Longer fusions carry a substantially higher risk, as the numbers above show. The location of where the fusion ends also plays a role: ending a fusion at a transition zone, like where the stiff lower back meets the more mobile mid-back, concentrates stress at that junction.
How ASD Feels
ASD can take several forms depending on what structure breaks down and where it happens. In the lumbar spine (lower back), it commonly causes new back pain or leg pain that feels different from the original problem. A herniated disc at the adjacent level can press on nerves and produce sciatica-type symptoms: shooting pain, numbness, or weakness traveling down one or both legs. If the spinal canal narrows (stenosis), you might notice that walking becomes harder and your legs feel heavy or cramped after a certain distance.
In the cervical spine (neck), ASD can cause neck pain, arm pain, tingling in the hands, or in more severe cases, difficulty with fine motor tasks like buttoning a shirt. The condition occurs in both the cervical and lumbar spine at roughly equal rates, about 2% to 4% per year.
One important distinction: many fusion patients show signs of wear at adjacent levels on imaging without ever developing symptoms. Radiographic changes alone, sometimes called “adjacent segment degeneration,” are far more common than true adjacent segment disease. ASD is only diagnosed when those structural changes actually produce pain or neurological symptoms that affect daily life.
How ASD Is Diagnosed
The diagnosis starts with the timing and pattern of symptoms. If you had a good result from fusion surgery and then develop new or different pain months to years later, ASD is one of the first things your surgeon will consider. Imaging, typically an MRI, will show whether the disc or joints at the neighboring level have deteriorated significantly. X-rays taken while you bend forward and backward can reveal abnormal motion at that segment. The key diagnostic step is confirming that the structural damage seen on imaging matches the location and type of symptoms you’re experiencing.
Treatment Without a Second Surgery
Not every case of ASD leads back to the operating room. When symptoms are mild to moderate, the same conservative approaches used for general spinal degeneration apply. Physical therapy focused on strengthening the core muscles that support the spine can reduce the load on the affected segment. Steroid injections into the epidural space or directly into an inflamed facet joint can provide temporary pain relief, sometimes lasting months. Anti-inflammatory medications, activity modification, and time are often enough for milder flare-ups.
The challenge is that the underlying mechanical problem, extra stress on the adjacent segment, doesn’t go away. Conservative treatment manages symptoms but doesn’t reverse structural damage. For some patients, symptoms stabilize and remain manageable indefinitely. For others, degeneration progresses to the point where surgery becomes necessary.
When a Second Surgery Is Needed
Roughly 8% to 12% of fusion patients undergo surgery for ASD within 5 to 10 years, depending on the study and the number of levels originally fused. The most common approach is extending the fusion to include the affected segment, which addresses the immediate problem but does shift stress to the next level up or down, potentially restarting the cycle.
Outcomes from revision surgery are generally favorable. In one study of patients who had revision surgery for cervical ASD about a decade after their original fusion, roughly 69% achieved good or excellent results. Serious complications were rare, and no patients in that series needed yet another surgery for residual symptoms. Recovery from revision surgery is similar to the original fusion: several weeks of restricted activity, gradual return to normal function over a few months, and a period of bone healing that can take six months to a year.
Can ASD Be Prevented?
Artificial disc replacement was developed partly to avoid this problem. By preserving motion at the treated level instead of locking it down, the theory is that neighboring segments won’t bear as much extra stress. In the cervical spine, artificial discs do maintain motion at the treated level. However, the evidence on whether this actually reduces the rate of adjacent-level surgery remains inconclusive. One large health technology assessment rated the evidence as low quality and could not confirm that disc replacement leads to fewer adjacent-level operations than fusion.
For patients who do undergo fusion, minimizing the number of fused levels when safely possible is one of the clearest strategies. Ensuring good overall spinal alignment at the time of surgery also matters, since poor alignment shifts extra load to adjacent segments from the start. After surgery, maintaining a healthy weight, staying physically active, and keeping the core muscles strong can help distribute forces more evenly across the spine, though none of these measures eliminate the risk entirely.