• Tianyuan Zhang, Shibin Shu, Wenting Jing, Qi Gu, Zezhang Zhu, Zhen Liu, Yong Qiu, Xu Sun, Bin Wang, and Hongda Bao.
• Spine Surgery, Nanjing Drum Tower Hospital, Medical School of Nanjing University, Nanjing, China.
• Eur Spine J. 2021 Jul 1; 30 (7): 1935-1942.

PurposeTo validate the predictability of S-line in Lenke 5C patients.MethodsLenke 5C patients with a minimum 2-year follow-up and with the lowest instrumented vertebra (LIV) at lower end vertebra were included. The S-line was defined as a line connecting the centers of concave-side pedicles of upper instrumented vertebra (UIV) and LIV on baseline films. The S-line tilt to right was defined as positive S-line status (S-line +) and tilt to left as S-line - status. Statistical analysis was performed between different subgroups.ResultsAmong the 92 patients, 69 patients had a left lumbar curve and 23 patients had a right lumbar curve. For left curves, the S-line + status had a significantly higher incidence of both proximal and distal decompensation. However, for right curves, the S-line - status was the risk factor. Thus, we modified the definition of S-line: The value of S-line tilt for right curves was opposite to that for left curves. Patients with modified S-line + showed a significantly higher incidence of both proximal and distal decompensation in Lenke 5C patients with both left and right curves (p < 0.001 and p = 0.010). In UEV group, patients with modified S-line + showed significantly higher incidence of proximal decompensation (P = 0.001). However, in UEV-1 group, the incidence of proximal decompensation was not statistically affected by modified S-line + (P = 0.281).ConclusionModified S-line + is a validated risk factor that predisposed to post-operative coronal decompensation in Lenke 5C AIS patients. Selecting UIV at one level caudal to UEV could be a possible solution if the modified S-line was positive.© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.

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