Adolescent idiopathic scoliosis (AIS) is the most common three-dimensional deformity of the spine that is typically characterized by curvature in both the coronal and sagittal planes. Selective thoracolumbar fusion (STLF) surgery, is an established corrective surgical technique for spinal deformities with excellent outcomes over time1. The objective of AIS corrective surgery encompasses the rectification of coronal and spinal rotation deformities while concurrently restoring the sagittal profile. However, some scholars suggested that correcting the Cobb angle and rotation deformity of the main thoracic curve has been associated with a sacrifice of sagittal plane aligament. Some researchers observed that significant reduction of thoracic kyphosis (TK) after the coronal deformity was corrected in their study3-5. In addition, Li et al3 found that both lumbar lordosis(LL) and sacral slope (SS) decreased after STLF surgery in their study. The sagittal plane of the spine column should be considered a chain-like structure, one section's change, that leads to compensatory changes in other segments, enables the maintenance of balance6. In addition, some scoloars suggested that the decrease in thoracic kyphosis may caused by vertebral derotation in STLF surgery. Postoperative shoulder imbalance (PSI) is a common complication that arises following STLF surgery, significantly impacting the appearance and satisfaction of patients8. The incidence of PSI varies within a range of 25% to 57%. It is imperative to identify the independent risk factors of PSI which can help in comprehending this phenomenon better and further aiding in deduction of the incidence rate. Although the research on the risk factors for PSI in AIS patients have been conducted for several years , no conclusively determination has been reached. Recently, scholars have been studying the relationship between the rotation of the thoracic spinal column and postoperative shoulder balance. Yagi et al.'s study10 has identified the preoperative rotation of the main thoracic apical vertebrae as a risk factor for PSI. Additionally, Masayoshi et al has reported on the relationship between the rotation of the proximal thoracic apical vertebrae and postoperative shoulder height disatance. In summary, it can be hypothesized that the preoperative and changes of postoperative sagittal spinal parameters may impact the postoperative shoulder balance among AIS patients. However, there is a paucity of literature investigating the effect of sagittal spinal parameters on PSI after STLF surgery. Therefore, the purpose of this study is to examine the correlation between the preoperative and postoperative alterations of sagittal spinal parameters and PSI.