Failure to Improve Lumbar Lordosis After Single-Level TLIF for Degenerative Spondylolisthesis Does Not Impair Clinical Outcomes at 8.6 Years Postoperatively: A Prospective Cohort of 32 Patients

<b>Background</b>: We aimed to analyze radiographic sagittal balance parameters in patients who underwent a TLIF procedure for single-level degenerative spondylolisthesis with a mean follow-up of 8.6 years and to determine whether lumbar lordosis affects long-term clinical outcomes. <b>Methods</b>: This prospective study included 32 patients who underwent single-level TLIF surgery for degenerative spondylolisthesis. Radiographic analysis of sagittal balance parameters and clinical examination including Oswestry Disability Index (ODI) scores were performed preoperatively, postoperatively, and at the last follow-up. A minimal clinically important difference threshold of 30% was accepted as clinically relevant. <b>Results</b>: Mean postoperative lumbar lordosis (LL) and segmental lordosis (SL) failed to improve postoperatively; nevertheless significant improvements in short- and long-term postoperative ODI scores were demonstrated (<i>p</i> < 0.001). Thoracic kyphosis (TK) and global sagittal balance parameters shifted anteriorly after 8.6 years (<i>p</i> < 0.001), but this increase did not affect clinical outcomes. <b>Conclusions</b>: Adequate decompression and solid bone fusion are foremost required to achieve improved long-term clinical outcomes in single-level TLIF procedures. In our studied cohort, failure to improve lordosis did not impair clinical outcomes postoperatively. With aging, thoracic kyphosis and anterior malalignment increase, and after 8.6 years, clinical improvements are starting to become insignificant.