� - Abstract - Study D Design: This is a retrospective study Objectives: We radiologically analyzed the correction of the sagittal imbalance and the proximal fusion level to prevent correc- tion loss and the usefulness of iliac screws in LDK. Summary o of tthe L Literature R Review: Complications can be encountered during fixation and fusion as most of the LDK patients are aged, and the osteoporosis that causes fixation loss is known to affect the loss of correction. Materials aand M Methods: We analyzed the cause of correction loss among 35 patients who underwent surgery and who were followed up for at least 1 year. All the patients had performed gait analysis before operation. The operative techniques were pedicle subtraction osteotomy and fixation to S1. For analyzing causes of correction loss, we analyzed the degrees of lumbar lor- dosis for the sagittal correction and the degrees of the preoperative thoracolumbar kyphosis for the proximal fusion range. For analyzing the usefulness of iliac screws, the subjects were divided into two groups: 1) the -iliac screw (23cases) group for the patients who were fixed without iliac screws and 2) the +iliac screw (12cases) group for the patients who were fixed with iliac screws. Results: There were no patients who had marked anterior pelvic tilt. It is important to correct the lumbar lordosis over 20�compared with the preoperative thoracic kyphosis. There are 10 cases of preoperative thoracolumbar kyphosis ≥ 10�and 25 cases of preoperative thoracolumbar kyphosis < 10�of the total 35 cases. Among 10 cases of preoperative thoracolumbar kyphosis ≥ 10� , 4 cases that were fixed to T10 had no sagit- tal correction loss, and 2 of the 6 cases that were fixed to T11 or T12 had sagittal correction loss. For the 25 cases of preoperative thoracolumbar kyphosis < 10� , 5 cases that were fixed to T10 had no sagittal correction loss and 1 of the 20 cases that were