Retrospective study.To investigate factors associated with cervical sagittal imbalance after cervical laminoplasty (LMP).Preoperative dynamic cervical sagittal alignment is an important predictor for changes in cervical sagittal alignment and clinical outcomes after LMP. However, the impact of preoperative dynamic cervical sagittal alignment on postoperative changes in the cervical sagittal vertical axis (cSVA) after LMP remains unclear. We hypothesized that preoperative cervical flexion and extension function are associated with the changes in cSVA and clinical outcomes and found potential risk factors for post-LMP cervical sagittal imbalance (CSI).Patients undergoing LMP at a single institution between January 2019 and December 2021 were retrospectively reviewed. The average follow-up period was 19 months. The parameters were collected before the surgery and at the final follow-up. We defined the changes in cSVA (△cSVA) ≤ -10 mm as the improvement group, -10 mm < △cSVA ≤ 10 mm as the stable group, and △cSVA > 10 mm as the deterioration group. Multivariate logistic regression was used to evaluate factors associated with postoperative CSI. The chi-square test was used to compare categorical data between groups. T-tests, ANOVA, Kruskal-Wallis tests, and Mann-Withney-Wilcoxon tests were used to assess the differences between radiographic and clinical parameters among groups. A receiver-operating characteristic curve (ROC) analysis was used to identify optimal cutoff values.The study comprised 102 patients with cervical spondylotic myelopathy. The Japanese Orthopedic Association (JOA) recovery rate was better in the improvement group and a significant aggravation in neck pain was observed in the deterioration group after surgery. Cervical Flex ROM (spine range of flexion) was significantly higher in the deterioration group. The multivariate logistic regression model suggested that greater Flex ROM and starting LMP at C3 were significant risk factors for postoperative deterioration of cervical sagittal balance. Receiver operating characteristic curves showed that the cut-off value for preoperative Flex ROM was 34.10°.Preoperative dynamic cervical sagittal alignment influences postoperative cervical sagittal balance after LMP. Cervical LMP should be carefully considered for patients with a preoperative high Flex ROM, as cervical sagittal imbalance is likely to occur after surgery.3.Copyright © 2023 The Author(s). Published by Wolters Kluwer Health, Inc.