Single Level Spinal Fusions: Does Postoperative Alignment Matter?

Introduction: Factors contributing to lumbar fusion revision remain unclear, with causes including recurrence of stenosis, non–union, and adjacent segment disease (ASD). The primary objective of this study was to characterize the postoperative alignment of adjacent segments after single-level lumbar interbody fusions and evaluate predictors of ASD development within the first 2 years after fusion surgery.

Methods: This retrospective review examined 40 patients treated with single-level lumbar interbody fusion between 2018 and 2023. Patients were divided by radiographic changes at adjacent segments (ASD) around a spinal fusion (n=18) and non-ASD (n=22). The criteria for ASD was defined as a decrease in adjacent disc height of >3mm, intervertebral angle changes in flexion of >5 degrees, and listhesis of >2mm when compared to preoperative films between 3 months and 2 years after surgery. Clinical data collected included demographics, operative details, and pre- and post-operative deformity measurements. T-test and logistic regressions were used to evaluate variables as predictors for development of ASD.

Results: Mean postoperative spinopelvic parameters showed no statistical difference between patients who developed ASD and those who did not. Patients with radiographic ASD underwent TLIF procedures 100% of the time compared to 86% for Non-ASD patients (p=0.05). Logistic regression revealed significantly higher rate of reoperation within 2 years for radiographic ASD patients compared to Non-ASD patients (OR: 40.25, 95% CI: 3.84 - 421.6, p=0.02) as well as when corrected for patient BMI and Age (OR: 6.79, 95% CI: 0.99 - 46.6, p=0.05). Additionally, BMI was associated with increased risk of radiographic ASD (OR: 1.18, 95% CI: 1.03 - 1.36, p=0.01).

Conclusion : Patients undergoing anterior fusion procedures may have a lower risk of ASD within the first 2 years after surgery whereas elevated BMI may increase risks of ASD. Single level lumbar interbody fusion patients with radiographic ASD have an increased risk of reoperation within 2 years.