Decompression With or Without Fusion Across Subgroups With Degenerative Lumbar Spondylolisthesis

Background: Randomized trials have shown limited benefits and increased risks of adding spinal fusion surgery to decompression for degenerative spondylolisthesis. Decompression with fusion has increasingly been used in the United States. Objective: To examine the comparative effectiveness of decompression with fusion versus decompression alone for patient subgroups. Design: Cohort study using the target trial framework. Setting: Norwegian Registry for Spine Surgery and nested NORDSTEN-DS (Norwegian degenerative spondylolisthesis and spinal stenosis) randomized trial. Patients: Adults aged 18 to 80 years with lumbar degenerative spondylolisthesis and symptomatic back or leg pain lasting at least 3 months. Intervention: Lumbar spinal decompression surgery with fusion versus lumbar spinal decompression surgery alone. Measurements: The primary outcomes were Oswestry Disability Index (ODI) score and reoperation at 12 months. Linear regression models with inverse probability weighting to control for baseline confounding were used to obtain effect estimates with 95% CIs for decompression with fusion versus decompression alone for prespecified subgroups, including sex, age, smoking, body mass index (BMI), back pain intensity, and American Society of Anesthesiologists (ASA) grade. Results: Of 2252 patients, 236 were in the NORDSTEN-DS randomized trial. The mean age was 66 years, and 1576 (70%) women were included. A total of 1446 patients had decompression alone, and 806 had decompression with fusion; respective unadjusted baseline ODI scores were 38.9 (SD, 14.9) and 41.4 (SD, 14.7). At 12 months, the ODI score was 22.3 (95% CI, 15.5 to 29.1) for decompression alone and 20.0 (CI, 13.9 to 26.2) for decompression with fusion; the mean difference was 2.2 (CI, −1.6 to 6.1). In exploratory analyses, the ODI score was worse for decompression with fusion for men with BMI of 30 kg/m 2 or higher. Reoperation risk at 12 months did not differ. Limitation: Possible residual confounding. Conclusion: Patient subgroups did not have differential effects from the addition of fusion to decompression at 12 months. Primary Funding Source: Research Council of Norway.