Effect of Single-Segment versus Two-Segment Pedicle Screw Fixation on Postoperative Sagittal Balance and Cranial Adjacent Segment Disease in L4-L5 Spondylolisthesis

Aim: To evaluate the effects of single-segment versus two-segment pedicle screw fixation on adjacent segment disease (ASDis) and lumbar sagittal balance in patients with L4-L5 spondylolisthesis. Materials and Methods: This retrospective study included 35 patients who underwent lumbar fusion for L4-L5 spondylolisthesis between January 2020 and January 2025. Patients were divided into single-segment (SS) and two-segment (TS) groups: SS (L4-L5 fusion, n = 19) and TS (L3-L4-L5 fusion, n = 16). Clinical outcomes were assessed using the Visual Analog Scale (VAS) and the Oswestry Disability Index (ODI). Radiological parameters, including lumbar lordosis (LL), sagittal vertical axis (SVA), and sacral slope (SCS), were measured. Adjacent segment degeneration (ASDeg) was evaluated using Modified Pfirrmann Grades. The follow-up period was 6 months postoperatively. Results: Both groups showed significant improvement in VAS and ODI scores postoperatively. At 6-month follow-up, the TS group demonstrated greater improvement (VAS: P =0.028; ODI: P =0.042). The SS group exhibited higher Pfirrmann scores, indicating greater ASDeg, compared to the TS group ( P P > 0.05). Conclusion: Both single-segment and two-segment fixation improve clinical and radiological outcomes in L4-L5 spondylolisthesis. However, two-segment fixation offers advantages in preventing adjacent-segment degeneration and maintaining radiographic parameters.