Objective
To determine the optimal targets of the L1 pelvic angle (L1PA) that minimize the risk of both proximal junctional kyphosis (PJK) and pelvic nonresponse (PNR) following adult spinal deformity (ASD) surgery.
Methods
A retrospective study was conducted on 323 patients who underwent fusion surgery from the low thoracic spine (T9–12) to the pelvis and were followed up for 2 years. Risk factors for PJK and PNR were evaluated separately using multivariate logistic regression analysis. Receiver operating characteristic (ROC) curve analyses were performed to identify L1PA cutoff values predictive of PJK and PNR across 3 pelvic incidence (PI) categories: <45°, 45°–60°, and ≥60°. L1PA thresholds were defined to delineate “ideal” alignment.
Results
Risk factor analyses revealed that low L1PA was an independent risk factor for PJK (odds ratio [OR], 0.927; p=0.019), while high PI–LL (OR, 1.101; p<0.001) and high L1PA (OR, 1.249; p<0.001) were significant risk factors for PNR. On ROC curve analyses, optimal L1PA ranges were 2.5°–4.5° for PI<45°, 8.7°–12.6° for PI 45°–60°, and 15.1°–17.3° for PI≥60°. Patients within these ideal L1PA ranges had significantly lower rates of both PJK and PNR compared to those exceeding ideal L1PA ranges.
Conclusion
This study demonstrated that optimal correction based on these L1PA targets reduced the risk of both PJK and PNR. Therefore, these L1PA targets can serve as reliable alignment goals to optimize surgical outcomes in ASD surgery.

Objective
To determine the clinical impact of the baseline sagittal imbalance severity in patients with adult spinal deformity (ASD).
Methods
We retrospectively reviewed patients who underwent ≥ 5-level fusion including the pelvis, for ASD with a ≥ 2-year follow-up. Using the Scoliosis Research Society-Schwab classification system, patients were classified into 3 groups according to the severity of the preoperative sagittal imbalance: mild, moderate, and severe. Postoperative clinical and radiographic results were compared among the 3 groups.
Results
A total of 259 patients were finally included. There were 42, 62, and 155 patients in the mild, moderate, and severe groups, respectively. The perioperative surgical burden was greatest in the severe group. Postoperatively, this group also showed the largest pelvic incidence minus lumbar lordosis mismatch, suggesting a tendency towards undercorrection. No statistically significant differences were observed in proximal junctional kyphosis, proximal junctional failure, or rod fractures among the groups. Visual analogue scale for back pain and Scoliosis Research Society-22 scores were similar across groups. However, severe group’s last follow-up Oswestry Disability Index (ODI) scores significantly lower than those of the severe group.
Conclusion
Patients with severe sagittal imbalance were treated with more invasive surgical methods along with increased the perioperative surgical burden. All patients exhibited significant radiological and clinical improvements after surgery. However, regarding ODI, the severe group demonstrated slightly worse clinical outcomes than the other groups, probably due to relatively higher proportion of undercorrection. Therefore, more rigorous correction is necessary to achieve optimal sagittal alignment specifically in patients with severe baseline sagittal imbalance.