 This study found that caudal spine segments had a sequential effect on cranial spine segments. Specifically, thoracic kyphosis, TK, sagittal vertical axis, SVA, and cervical lordosis, CL, were significantly related to high thoracic spinal sagittal slopes, T1S. Additionally, pelvic posterior rotation and thoracic compensation were two crucial factors protecting against increased T1S in patients with ankylosing spondylitis, ASD. This article was authored by Chengxin Liu, Yongjin Li, Xiong Yu Li, and others.