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Objective: To assess which radiological alignment parameters are associated with a satisfactory long‐term clinical outcome after performing lumbar spinal fusion for treating degenerative spondylolisthesis. Methods: This single‐center prospective study assessed the relation between radiological alignment parameters measured on standing lateral lumbar spine radiographs and the patient‐reported outcome using four different questionnaires (COMI, EQ‐5D, ODI and VAS) as primary outcome measures (level of evidence: II). The following spinopelvic alignment parameters were used: gliding angle, sacral inclination, anterior displacement, sagittal rotation, lumbar lordosis, sacral slope, pelvic tilt and pelvic incidence. Furthermore, the length of stay and perioperative complications were documented. Only cases from 2013 to 2015 of low‐grade degenerative lumbar spondylolisthesis (Meyerding grades I and II) were considered. The patients underwent open posterior lumbar fusion surgery by pedicle screw instrumentation and cage insertion. The operative technique was either a posterior lumbar interbody fusion (PLIF) or a transforaminal lumbar interbody fusion (TLIF) performed by three different senior orthopedic surgeons. Exclusion criteria were spine fractures, minimally invasive techniques, underlying malignant diseases or acute infections, previous or multisegmental spine surgery as well as preoperative neurologic impairment. Of 89 initially contacted patients, 17 patients were included for data analysis (11 males, six females). Results: The data of 17 patients after mono‐ or bisegmental lumbar fusion surgery to treat low‐grade lumbar spondylolisthesis and with a follow‐up time of least 72 months were analyzed. The mean age was 66.7 ± 11.3 years. In terms of complications two dural tears and one intraoperative bleeding occurred. The average body mass index (BMI) was 27.6 ± 4.4 kg/m2 and the average inpatient length of stay was 12.9 ± 3.8 days (range: 8–21). The long‐term clinical outcome correlated significantly with the change of the pelvic tilt (rs = −0.515, P < 0.05) and the sagittal rotation (rs = −0.545, P < 0.05). The sacral slope was significantly associated with the sacral inclination (rs = 0.637, P < 0.01) and the pelvic incidence (rs = 0.500, P < 0.05). In addition, the pelvic incidence showed a significant correlation with the pelvic tilt (rs = 0.709, P < 0.01). The change of the different clinical scores over time also correlated significantly between the different questionnaires. Conclusions: The surgical modification of the pelvic tilt and the sagittal rotation are the two radiological alignment parameters that can most accurately predict the long‐term clinical outcome after lumbar interbody fusion surgery. [ABSTRACT FROM AUTHOR]