Adjacent Segment Disease

What happens in adjacent segment disease

Spinal fusion joins two or more vertebrae with bone graft, screws and rods (or a cage and plate in the neck) so they heal into one solid unit. Fusion can relieve pain and stabilize the spine, but the fused levels no longer move. The levels just above and below take on more bending and twisting forces and higher disc pressure.

Over time, these adjacent levels may develop:

• disc degeneration and bulging or herniation
• thickening and arthritis of the facet joints
• narrowing of the spinal canal (spinal stenosis)
• slippage of one vertebra on another (spondylolisthesis)
• instability or a flat-back posture

Doctors distinguish two terms:

Imaging changes are common after fusion, but many people never develop symptoms.

Causes and risk factors

Researchers debate how much is due to the fusion itself and how much to the natural aging of a spine already prone to degeneration. Both play a part. Factors linked to a higher risk include:

• longer fusions involving more levels
• pre-existing degeneration at the adjacent level before surgery
• damage to the adjacent facet joint or ligaments during surgery
• poor spinal alignment (sagittal imbalance) after fusion
• older age, higher body weight and smoking
• osteoporosis
• fusion ending at certain transition zones, such as L5-S1 or the junction of the thoracic and lumbar spine

Symptoms

Symptoms are usually similar to those that led to the original surgery, often after a period of relief:

After lumbar (low back) fusion:

• returning low back pain
• sciatica: pain, tingling or numbness down a leg
• leg heaviness or pain when walking that eases with sitting or bending forward (neurogenic claudication from spinal stenosis)
• leg weakness

After cervical (neck) fusion:

• neck pain and stiffness
• arm pain, tingling or weakness (cervical radiculopathy)
• clumsy hands, balance problems or difficulty walking, which suggest pressure on the spinal cord (myelopathy)

Diagnosis

A spine specialist will compare your symptoms with your previous surgery and examine strength, sensation and reflexes. Tests include:

• X-rays, including standing and flexion-extension views to show alignment, slippage and instability, and the condition of the fusion and hardware
• MRI to show discs, nerves and spinal canal narrowing. Metal hardware can blur images near the fusion
• CT scan or CT myelogram if MRI is limited by hardware, or to check whether the fusion has healed
• Nerve studies if it is unclear which nerve is affected
• Diagnostic injections to confirm whether a particular joint or nerve is the pain source

Other causes of returning pain after fusion, such as a fusion that did not heal (pseudarthrosis), loose hardware, infection or hip and sacroiliac joint problems, are checked at the same time.

Treatment

Non-surgical treatment

Most people start here:

• Physical therapy: core and hip strengthening, posture training and walking programs
• Medicines: NSAIDs at the label or prescribed dose, and nerve pain medicines for sciatica or arm pain
• Epidural steroid injections or facet joint injections for short- to medium-term relief
• Radiofrequency ablation of facet joint nerves in selected cases
• Weight loss, stopping smoking and staying active

Surgery

Surgery is considered when symptoms are severe, there is progressive weakness or spinal cord compression, or several months of non-surgical treatment have not helped. Options include:

• Decompression (laminectomy) to relieve pressure on nerves, sometimes without extending the fusion
• Extension of the fusion to include the adjacent level
• Minimally invasive or lateral fusion techniques at the new level
• Cervical disc replacement at the adjacent level in selected neck cases, which preserves motion

Each further operation carries the risks of surgery and the possibility of degeneration at the next level.

Prevention

Surgeons try to reduce the risk by fusing only the necessary levels, protecting the adjacent joints during surgery, restoring good spinal alignment, and considering motion-preserving options such as disc replacement where appropriate. After surgery, maintaining a healthy weight, not smoking, regular exercise and core strengthening help protect the spine.

Frequently asked questions

What is adjacent segment disease?

It is degeneration of the spinal levels next to a spinal fusion that causes new symptoms, such as back or neck pain, leg or arm pain, numbness or weakness. It results from extra stress on these levels and natural aging of the spine.

How common is adjacent segment disease after fusion?

Changes on imaging are common, but symptomatic disease is less so. Studies suggest roughly 2 to 4% of patients develop symptoms per year after fusion, so a significant minority need treatment within 10 years. Risk varies with the type and length of fusion.

What are the symptoms of adjacent segment disease?

Typical symptoms are returning back or neck pain, sciatica or arm pain, tingling, numbness and weakness. Leg pain when walking that improves with sitting suggests spinal stenosis. Clumsy hands or balance problems after neck fusion suggest spinal cord pressure.

Can adjacent segment disease be treated without surgery?

Yes. Many people improve with physical therapy, medicines, injections and lifestyle changes. Surgery is reserved for severe pain that does not respond, progressive weakness or nerve compression, or spinal cord compression.

Can adjacent segment disease be prevented?

It cannot be completely prevented, but the risk can be lowered. Surgeons limit the number of fused levels and restore alignment. Patients can help by keeping a healthy weight, not smoking, and staying active with core strengthening exercises.