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Study Design: Retrospective cohort study., Objective: To determine whether the L1 pelvic angle (L1PA) can be used to predict quality of life outcomes for adults one year after L4-L5 fusion to treat degenerative spondylolisthesis., Summary of Background Data: L1PA is beneficial in the evaluation of preoperative and postoperative quality of life outcomes in patients undergoing surgery for spinal deformity. No studies have examined its utility in surgical patients with degenerative spinal disease., Methods: Patients undergoing L4-L5 posterolateral decompression and fusion or transforaminal lumbar interbody fusion for degenerative lumbar spondylolisthesis were grouped by preoperative and postoperative L1PA, and further stratified by cut offs of >7.2° and <7.2° based on previous literature. We also stratified patients by presence of an ideal calculated L1PA, defined as (0.5×Pelvic incidence) -21 +/-5°, as proposed by prior literature. Preoperative, one-year postoperative and Δ (postoperative minus preoperative) patient-reported outcome measures (PROMs) and radiographic measurements were collected., Results: Twenty-four patients were identified with preoperative L1PAs <7.2° and 132 with L1PAs >7.2°. Eighteen patients were identified with postoperative L1PAs <7.2° and 138 with L1PAs>7.2°. Sixty-five and fifty-seven patients were identified as having ideal calculated preoperative and postoperative L1PAs, respectively. When using absolute cutoffs, L1PA correlated with pelvic tilt, pelvic incidence, and pelvic incidence-lumbar lordosis mismatch (PI-LL). When using calculated L1PAs, L1PA correlated with lumbar lordosis, PI-LL, pelvic tilt and sacral slope. With respect to PROMs, no statistically significant differences existed between cohorts both preoperatively and at one-year postoperatively on either univariate and multivariate analyses., Conclusion: L1PA may be a helpful radiographic consideration that translates to clinically relevant outcomes in spinal deformity. However, it does not appear as predictive of patient outcomes after single-level fusion for patients with L4-L5 degenerative spondylolisthesis. Further studies are warranted to investigate the role of L1PA in degenerative spine patients., Competing Interests: The authors report no conflicts of interest., (Copyright © 2024 Wolters Kluwer Health, Inc. All rights reserved.)