• Zongshan Hu, Zhikai Qian, Weibiao Li, Jie Li, Ziyang Tang, Chen Ling, Yanjie Xu, Zhen Liu, Zezhang Zhu, and Yong Qiu.
• Division of Spine Surgery, Department of Orthopedic Surgery, Drum Tower Hospital of Nanjing University Medical School, Nanjing, China.
• Eur Spine J. 2024 May 1; 33 (5): 181618201816-1820.

Study DesignA prospective study.ObjectiveThe aim of this study was to investigate the PI change in different postures and before and after S2‑alar‑iliac (S2AI) screw fixation, and to investigate whether pre-op supine PI could predict post-op standing PI. Previous studies have reported PI may change with various positions. Some authors postulated that the unexpected PI change in ASD patients could be due to sacroiliac joint laxity, S2-alar-iliac (S2AI) screw placement, or aggressive sagittal cantilever technique. However, there was a lack of investigation on how to predict post-op standing PI when making surgical strategy.MethodsA prospective case series of ASD patients undergoing surgical correction with S2AI screw placement was conducted. Full-spine X-ray films were obtained at pre-op standing, pre-op supine, pre-op prone, as well as post-op standing postures. Pelvic parameters were measured. Spearman correlation analysis was used to determine relationships between each parameter.ResultsA total of 83 patients (22 males, 61females) with a mean age of 58.4 ± 9.5 years were included in this study. Pre-op standing PI was significantly lower than post-op standing PI (p = 0.004). Pre-op prone PI was significantly lower than post-op standing PI (p = 0.001). By contrast, no significant difference was observed between pre-op supine and post-op standing PI (p = 0.359) with a mean absolute difference of 2.2° ± 1.9°. Correlation analysis showed supine PI was significantly correlated with post-op standing PI (r = 0.951, p < 0.001).ConclusionThis study revealed the PI changed after S2AI screw fixation. The pre-op supine PI can predict post-op standing PI precisely, which facilitates to provide correction surgery strategy with a good reference for ideal sagittal alignment postoperatively.© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.

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