Spinal fusion and artificial disc replacement: how the two operations compare

Fusion: bone joining and stability

In fusion, bone graft material is placed where the surgeon wants vertebrae to join. A graft may come from the patient, a bone bank, or a substitute. Plates, screws, rods, or cages may hold the area still while the graft joins the bones. The implant hardware supports the process; the intended lasting change is a solid connection between the vertebrae. MedlinePlus explains the graft and fixation methods.

OrthoInfo describes fusion in connection with conditions including disc degeneration, spinal instability, spinal narrowing, fractures, and abnormal spinal curvature. It also distinguishes fusion from decompression, which removes tissue pressing on nerves. An operation can combine these purposes, so the name fusion alone may not describe everything planned. The OrthoInfo fusion explanation provides that distinction; the guide to disc and nerve conditions explains related terms.

OrthoInfo explains that the surgical approach can be from the front, back, or side. The approach and the way the vertebrae are joined are distinct parts of a fusion plan. Its discussion also describes imaging as part of locating the source of pain. The same operation name can therefore cover different routes and different structures, making the full proposed procedure more informative than its shortened label. OrthoInfo describes approaches and assessment.

Disc replacement: an implant intended to move

An artificial disc sits between vertebrae after the damaged disc has been removed partly or completely. NICE describes replacement in the lumbar spine, or lower back, through an approach from the abdomen. In the neck, or cervical spine, the surgeon approaches from the front, relieves pressure on nerve structures, removes damaged disc material, and places the implant. The aim is to preserve movement at the treated segment. NICE lumbar procedure; NICE cervical procedure.

That aim needs to be separated from a demonstrated long-term benefit. NICE identifies preservation of mobility, disease in neighboring spinal segments, and further surgery as subjects needing continued research. A moving implant is a mechanical description, rather than a promise that nearby discs will remain unchanged. The step-by-step explanation of disc replacement follows the procedure in more detail. NICE cervical recommendations.

The mechanical difference in outline

Which patients the guidance describes

For lumbar disc replacement, NICE describes selection by a team with specialist expertise in degenerative spinal disease. Its recommendations concern patients whose conservative care has failed or cannot be used, with arrangements for consent, clinical oversight, and audit. The cervical recommendations describe use in specialist units that regularly undertake neck surgery. These are conditions surrounding a procedure's use, rather than a checklist that establishes someone's eligibility. NICE lumbar recommendations; NICE cervical recommendations.

Approval records from the U.S. Food and Drug Administration (FDA) show how specific an indication can be. The lumbar record describes patients whose skeletons have finished developing with disc-related back pain and degeneration established from history and imaging after unsuccessful conservative treatment. The cervical record describes disc removal for persistent nerve-root or spinal-cord problems associated with disc herniation or bony growths. Both records warn that original labeling may differ from later labeling. FDA lumbar approval record; FDA cervical approval record.

What lumbar comparisons reported

A 2012 Cochrane review found that statistically significant differences favoring disc replacement did not exceed accepted clinically important differences in short-term pain, disability, or quality of life. The authors emphasized the highly selected study population. They also found that prevention of neighboring-level disease and facet-joint degeneration had not been properly assessed. Its conclusions therefore do not establish that preserving motion prevents future problems or predicts an individual result.

A 2014 meta-analysis of randomized trials reported advantages for disc replacement in physical function, pain, and hospital-stay duration, while reporting no significant differences in complications or further surgery. The authors said that benefits concerning movement preservation and long-term complications remained unproved. These findings describe the patients and comparisons included in that review, and cannot predict the outcome for an individual patient.

A 2009 randomized lumbar trial report found clinical outcomes consistent with the earlier conclusion that disc replacement was not inferior to the fusion comparison studied. It reported no statistical difference between groups in clinical outcomes, alongside differences in employment and disability measures. The abstract also describes incomplete follow-up among eligible participants. That context matters when interpreting the reported group results; they cannot provide a personal forecast.

What cervical comparisons reported

A 2013 review of randomized cervical trials found low-to-moderate-quality evidence favoring arthroplasty, often with statistical significance. However, differences in the main outcomes were small and were not clinically relevant. The review concerned cervical degenerative disc disease with nerve-root or spinal-cord symptoms. Results for those selected study participants cannot establish the likely benefit for another person or be transferred automatically to lower-back surgery.

A 2016 meta-analysis of cervical trials associated disc replacement with fewer repeat operations than anterior disc removal and fusion. The authors explicitly called for caution and additional studies. The abstract identifies possible publication bias, meaning that smaller studies with negative findings or no difference may have remained unpublished. This is evidence about study groups, rather than a guarantee that a moving implant will avoid further surgery for any individual.

Risks belong in the comparison too

OrthoInfo lists infection, bleeding, graft-site pain, recurring symptoms, nerve or blood-vessel injury, blood clots, and failure to achieve a solid fusion among fusion complications. NICE lists possible disc-replacement complications including implant movement or loosening, wear-related problems, nerve injury, infection, and the need for further surgery. The exact risks discussed depend on the location and procedure. OrthoInfo fusion risks; NICE lumbar safety information; NICE cervical safety information.

MedlinePlus cautions that fusion does not always improve pain and that the degree of improvement is hard to predict, even with imaging. That uncertainty belongs alongside the mechanical explanation and comparative research. The guide to shared decisions and appointment questions provides a place to organize questions about an individual case. The glossary definition of fusion offers a brief reminder of the central term. MedlinePlus on the limits of prediction.

After fusion, MedlinePlus describes increased stress on the spinal segments above and below the joined area because the fused area no longer moves. This explains why neighboring segments appear so often in comparative research. It does not, by itself, answer whether disc replacement prevents those problems: the Cochrane review found that this intended benefit had not been properly assessed. Anatomy, a proposed advantage, and evidence of an outcome are separate parts of that discussion. MedlinePlus on neighboring segments; Cochrane review conclusions.

The spinal segment in outline