Can lumbar fusion contribute to degeneration at nearby spinal segments?

Lumbar fusion eliminates motion at treated levels, making load redistribution to the remaining mobile segments biologically and mechanically expected. The evidence strongly supports this biomechanical change; its role as a direct cause of later adjacent-segment degeneration in an individual patient remains plausible rather than definitively proven.

Biomechanical and clinical evidence

• Cadaveric studies show 45–73% higher intradiscal pressure at levels adjacent to a fusion, along with greater flexion motion.
• Computational and musculoskeletal models consistently find increased adjacent-level range of motion, disc stress/pressure, shear and passive moments, and facet contact forces.
• Clinical series and meta-analyses report radiographic degeneration adjacent to posterior lumbar fusions, while symptomatic adjacent-segment disease and reoperation occur in a smaller subset. Radiographic change, symptoms, and need for revision are distinct outcomes.

Mechanisms and modifiers

• The coherent mechanism is increased motion and loading in unfused discs and facet joints after the fused segment can no longer contribute normally to spinal motion. Repetitive disc pressure, shear, and facet loading could accelerate degenerative processes.
• Longer fusion constructs appear to amplify adjacent-level motion and facet stress; fusion of three or more levels has been associated clinically with greater degeneration or revision risk.
• Sagittal alignment may matter: increased sagittal vertical axis, inadequate lumbar lordosis, and pelvic-incidence–lumbar-lordosis mismatch are frequently associated with adjacent degeneration, although long-term findings are not fully consistent.
• In an 83-year-old, pre-existing adjacent-level degeneration, bone health, body habitus, smoking history, facet-joint injury, and alignment may substantially influence risk alongside the fusion itself.

Bottom line

• Lumbar fusion reliably increases mechanical demands at adjacent mobile levels and is associated with adjacent radiographic degeneration. Increased stress is a credible contributor to degeneration, particularly with longer constructs or unfavorable alignment, but it should not be viewed as the sole or certain cause of future adjacent-level symptoms in any one patient.