Fig. 4

Schematic diagram of preoperative prediction for sagittal imbalance. a-c Two or three preoperative parameters met the thresholds of TPA > 40.9°, PI—LL > 32.5° and SVA > 13.7 cm, a high risk of sagittal imbalance was predicted following one-level three column-osteotomy, and additional osteotomies was recommended. d The goal for preventing postoperative sagittal imbalance was to reconstruct the immediate postoperative SVA of ≤ 7.4 cm