Abstract： Objective:To analyze the relationship between post-operative proximal junctional kyphosis (PJK) and C 2-femoral heads center (C 2-FH), pelvic fixation in adult spinal deformity (ASD) patients, so as to provide a reference for the preoperative decision-making and the postoperative intervention timely. Methods:It was a retrospective study that analyzed 34 cases of ASD patients who underwent posterior pedicle screw fixation in Nanjing Drum Tower Hospital between January 2017 and May 2017. ASD patients were divided into two groups according to fixation options: the sacroiliac fixation group and the non-sacroiliac fixation group. The spine-pelvis parameters were evaluated on full-length X ray films of spine at preoperatively, 2 weeks postoperatively and the last follow-up, and the incidence of PJK was recorded.Results:A total of 34 ASD patients (3 males and 31 females) were included in this study, with an average age of (58±6) years. The mean follow-up period was (2.9±1.0) years (2.0-4.0 years). The age, follow-up time and various spine-pelvis parameters showed no significant differences between the two groups (all P>0.05). The immediate postoperative C 2-FH in the sacroiliac fixation group was significantly lower than that in the non-sacroiliac fixation group [(-69.46±30.85) mm vs (-31.62±15.31) mm, P<0.001]. The incidence of PJK was as high as 50.0% (8/16) in patients with sacroiliac fixation, but it was only 22% (4/18) in patients without sacroiliac fixation ( P=0.016). At the last follow-up, the C 2-FH of both groups were both higher than -20 mm (both were approximately -15 mm, P=0.976), indicating that the C 2-FH was compensated in both groups. Due to the loss of the distal compensation ability, the incidence of PJK in the sacroiliac fixation group was higher than that in the non-sacroiliac fixation group. Due to the fixation of pelvis and most of lumbar spine, no significant differences were found in lumbar lordosis (LL), pelvic tilt (PT) and sacral slope (SS) at the last follow-up in both groups when compared with those after the operation (all P>0.05); while the thoracic kyphosis (TK) and cervical lordosis (CL) increased significantly (both P<0.05) to compensate C 2-FH at the last follow-up. Conclusion:It′s demonstrated that C 2-FH< -2 cm and pelvic fixation are high risk factors of PJK in ASD patients. It is suggested that both global sagittal balance and pelvic fixation should be considered in decision-making and corrective surgery, rather than only focusing on spine-pelvic parameters.