The Risk Factors of Early and Late-Onset Adjacent Segment Degeneration after Thoracolumbar Fusion Surgery

Abstract

Adjacent segment degeneration (ASD) is a long-term complication that can occur after thoracolumbar fusion surgery. This study was undertaken to determine the risk factors of earlyonset ASD. Methods: We retrospectively reviewed patients who underwent thoracolumbar fusion at our institute for lumbar disease from January 2008 to December 2018. Potential risk factors examined included radiologic factors such as postoperative sagittal alignment, preexisting disc degeneration, and facet degeneration. For the analysis, patients were dichotomized based on times to ASD, that is, <1 year (the early group) and ≥1 year (the late group). Results: During the 11-year study period, 693 patients underwent thoracolumbar fusion, and 92 (13.28%) patients developed ASD; 34 (4.9%) during the first postoperative year and 58 (8.4%) at more than 1 year after surgery. The proportion of patients with a longer fusion length was greater in the early group (p=0.0045). Postoperative lumbar lordosis (LL; p=0.0007) and sagittal vertical axis (SVA) (p=0.009) values were significantly different in the 2 groups, sacral slope (SS; p<0.05) was smaller in the early group, and pelvic tilt (PT; p=0.03) was larger in the early group. However, pelvic incidence (PI; p=0.72) was no different in the 2 groups. Conclusion: The risk factors of early-onset ASD after thoracolumbar fusion surgery were confirmed to be the degree of fusion length and LL after surgery. SVA was found to possibly contribute to early-onset ASD. Although PI was similar in the 2 study groups, SS and PT were significantly different. So when you perform spinal fusion surgery, you should minimize fusion length and consider sagittal alignment.