Objective:To compare the efficacy of reduction and in situ intervertebral fusion fixation in the treatment of degenerative lumbar spondylolisthesis.Methods:A total of 182 patients (92 males and 90 females) with L 4 degenerative lumbar spondylolisthesis of Meyerding's classification of grade I and grade II, aged (62.6±6.8) years (range, 57-73 years), who underwent posterior L 4, 5 internal fixation and interbody fusion in the Department of Spinal Surgery, the Second Hospital of Shanxi Medical University, were retrospectively analyzed from January 2019 to December 2022. There were 105 cases of I-degree spondylolisthesis and 77 cases of II-degree spondylolisthesis. According to the operation method, the patients were divided into reduction intervertebral fusion fixation (reduction group) and in situ intervertebral fusion fixation group (in situ group). Imaging parameters such as lumber lordosis (LL), pelvic incidence (PI)-LL, L 3, 4 intervertebral space heights, fusion segment angle, and sagittal vertical axis (SVA) were measured on the pre- and post-surgical lumbar spine lateral radiographs. The visual analogue scale (VAS) and Oswestry Disability Index (ODI) of low back pain were recorded before and after surgery. The differences in clinical and imaging parameters were compared between reduction and in situ fusion group. Results:All 182 patients successfully completed the surgery and were followed up for 12.0±2.4 months (range, 9-15 months). The LL of the reduction group before surgery, immediately after surgery, and at the last follow-up were 46.9°±7.1°, 57.2°±5.9°, 55.6°±5.5°, respectively, with statistically significant differences ( F=87.61, P<0.001), with immediate and final follow-up being smaller than those in the in situ fixation group. The LL of the in situ fixation group before surgery, immediately after surgery, and at the last follow-up were 47.8°±7.2°, 50.5°±7.0°, and 48.7°± 6.4°, respectively, with no statistically significant difference ( F=2.83, P=0.062). The immediate and final follow-up of LL in the reduction group was lower than those in the in situ fixation group ( P<0.05). The fusion segment angles of the reduction group before surgery, immediately after surgery, and at the last follow-up were 14.2°±5.1°, 23.2°±4.7°, 23.2°±4.7°, respectively, with statistically significant differences ( F=152.87, P<0.001), with immediate and final follow-up after surgery being greater than before surgery. The fusion segment angles of the in situ fixation group before surgery, immediately after surgery, and at the last follow-up were 15.4°±5.9°, 18.2°±5.5°, and 17.4°±5.1°, respectively, with statistically significant differences ( F=4.69, P=0.009), with immediate and final follow-up being greater than before surgery. The fusion segment angulation in the reduction group was greater than that in the in situ fixation group at both the immediate and final follow-up ( P<0.05). The SVA of the reduction group before surgery, immediately after surgery, and at the last follow-up were 16.9±18.2 mm, 9.5±12.0 mm, and 8.7±11.3 mm, respectively, with statistically significant differences ( F=11.32, P<0.001), with immediate and final follow-up being smaller than before surgery. The SVA of immediately after surgery and at the last follow-up were both smaller than before surgery. The SVA of the in situ fixation group before surgery, immediately after surgery, and at the last follow-up were 16.4±17.2 mm, 14.3±15.5 mm, and 13.8±15.0 mm, respectively, with no statistically significant difference ( F=0.57, P=0.576). The SVA of the reduction group at immediate and final follow-up was lower than that of the in situ fixation group ( P<0.05). Conclusion:Both reduction and in situ intervertebral fusion fixation can effectively relieve the clinical symptoms of patients. Fusion fixation after reduction can improve the angulation of fusion segments to form segmental kyphosis, which is more conducive to improving SVA.