This study aimed to explore the impact of T helper 17 (Th17)/regulatory T (Treg) cells imbalance and inflammatory factors (IL-1b, IL-18, and TNF-a) on sagittal balance in patients with thoracolumbar kyphosis due to ankylosing spondylitis (AS) following vertebral column decancellation (VCD), to clarify the predictive efficacy of the Th17/Treg ratio and IL-1b, IL-18, and TNF-a in post-operative sagittal imbalance. Here, IL18 is linked to ankylosing spondylitis.