Long-Term Risks of Spinal Fusion

Why Does It Happen?

1. Increased Mechanical Stress

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.

2. Surgical Impact on Neighboring Structures

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:

• Fusion alone: ASD rate of 35.2%
• Fusion with laminectomy at the adjacent level: ASD rate of 57.5%

(Simonetta B et al., Spine 2025)

3. Screw Placement

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.

4. Spinal Alignment During Fusion

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.

5. Number of Levels Fused

Limiting fusion to the minimum necessary number of levels is important. The five lumbar vertebrae are designed for significant movement in daily life. Each level that is fused means fewer remaining levels to share the workload, increasing the burden on each one.