Oral Presentation 51st International Society for the Study of the Lumbar Spine Annual Meeting 2025

Introduction: Despite a marked increase in the rate of combined anterior-posterior column (“AP”) lumbar fusions as a percent of total fusions in the U.S. since 2016, no large-scale examination of its safety has been performed. We compared rates of all-cause readmission and pseudoarthrosis through 6 years of post-operative surveillance, and surgical complications at 1 year post-operatively, between single column (anterior or posterior fusions) and AP fusions among Medicare beneficiaries.

Methods: We included fee-for-service Medicare beneficiaries undergoing thoracolumbar, lumbar, and lumbosacral fusion from a 100% sample of inpatient claims from 2016-2021, accessed via the Virtual Research Data Center. Beneficiaries with dual eligibility, social security disability insurance or end stage renal disease entitlement were excluded. International Classification of Disease (ICD-10) procedure codes were used to classify admissions by columns fused (anterior only, posterior only, combined AP) based on Medicare definitions. Each admission was linked to subsequent inpatient and Part B claims in order identify the incidence of readmission, pseudoarthrosis, and 17 types of post-operative complications as published by Engler et. al. (2023). The days between discharge and beneficiary’s first readmission (and pseudoarthrosis) was calculated for a time-to-event Cox proportional hazards survival analysis comparing differences based on columns fused. Robust logistic regression was used to estimate the relative risk (as odds ratios) for the difference in complications at 1 year following discharge across columns fused. All models were adjusted for age, sex, race, indication, and Charlson comorbidity index.

Results: After exclusions, a total of 359,564 beneficiaries were evaluated, including 141,854 (39.5%) beneficiaries with AP fusion. As a percent of total lumbar fusions, AP column increased from 25.3% in 2016 to 53.0% in 2021. Compared to those undergoing single column fusions, those undergoing AP fusion were significantly younger, had a lower comorbidity burden, and were more likely to have an adult scoliosis indication. Relative to posterior column fusions, the time to readmission was significantly lower among anterior column (HR 0.93, 95%CI 0.92 - 0.94, p<0.001) and AP fusions (HR 0.90; 95%CI 0.89 - 0.91, p<0.001) based on adjusted 6-year survival analysis. The likelihood of pseudoarthrosis was also lower for anterior (HR 0.82 95%CI 0.78 - 0.86) and AP fusion (HR 0.95 95%CI 0.91 - 0.99, p=0.024), compared to posterior column fusion. Similarly, the risk any post-operative complication at 1 year was lower among AP (OR 0.85 95%CI 0.84 - 0.87, <0.001) and anterior column fusion (OR 0.82 95%CI 0.82 - 0.84, <0.001) compared to posterior column fusions.

Discussion: Combined AP lumbar column fusions are now more common than single column lumbar fusions in an older population. Although selection bias cannot be fully ruled out, the adjusted rates of readmission, pseudoarthrosis, and postoperative complications were lower for AP fusion compared to posterior fusion. While these findings may help guide clinical decision making, future research should focus on whether AP fusion improves patient-reported outcomes for pain, function, and disability.