With a deepening understanding on the impact of sagittal alignment in spine deformities, research on adolescent idiopathic scoliosis (AIS) has expanded beyond coronal to include sagittal deformities [
1-
5]. In AIS, posterior global alignment—in other words, negative sagittal vertical axis—and/or hypokyphosis in the thoracic spine are commonly observed, resulting in cervical kyphosis as a compensatory mechanism [
2,
4]. Previous studies have reported that the cervical kyphosis (CK) present in up to 60% of AIS patients [
4]. These findings suggest that contemporary surgical strategies for AIS have increasingly focused on restoring sagittal parameters—particularly thoracic kyphosis (TK) —in addition to correcting the coronal Cobb angle, with careful consideration of cervical sagittal alignment (CSA) [
1-
5].
With regard to surgical treatment in AIS, both the T1 slope and TK are recognized as pivotal contributors to postoperative compensation of CSA [
2,
4]. Given that the thoracic spine are not a simple arc, but comprise distinct proximal, mid, and distal segments in TK, these findings suggest that the proximal TK may play a key role in postoperative changes of cervical spine shape [
6,
7]. Although the Lenke 2 curve includes a structural curve in the proximal thoracic region, the relationship between CSA and TK is not yet been clearly established in Lenke 2 AIS patients who underwent deformity correction.
The authors in this article [
8] investigated the incidence of cervical malalignment (CM) and its associated radiological factors following posterior correction and spinal fusion (PSF) with Lenke 2 AIS. Specifically, the authors examined the influencing factors for postoperative CSA and TK (proximal and main TK). In this single institution retrospective analysis involving 102 Lenke 2 AIS patients, a high incidence of CM (59.3%) was observed preoperatively, characterized by kyphotic cervical lordosis, a lower T1 slope, and diminished proximal TK (T1–5). At a minimum follow-up of 2 years postoperatively, an increase in proximal TK was found to elevate the T1 slope, which in turn contributed to the improvement in CSA. On basis of these findings, the authors concluded that PSF-induced enhancement of proximal TK, rather than main TK (T5–12), played a central role in the restoration of CSA.
The authors should be commended for their insightful interpretation for the role of proximal TK in influencing T1 slope and the subsequent changes in the CSA, based on the regional contribution of the thoracic spine to overall TK in Lenke 2 AIS. This study offers valuable insight into the importance of restoring proximal TK to prevent postoperative CM, highlighting the compensatory mechanisms of CSA following PSF in AIS. However, with the nature of study design, causal relationship was not fully established in CSA as a limitation in this study. An interesting point highlighted in this study [
8] is that complete correction of CK was not achieved in all patients. As the authors noted, the reactive restoration of cervical lordosis is a complex process, likely influenced by multiple factors including the C2 slope, TK, spinal flexibility, and overall spinal morphology [
8]. Accordingly, further study may be warranted to identify the key determinants of cervical lordosis restoration in future.
This study supports the correction strategies take into account CSA by focusing on the proximal TK and T1 slope in patients with patients with Lenke 2 AIS. The authors provided a valuable foundation and more plausible evidence in the surgical treatment of AIS.
NOTES
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Conflict of Interest
The author has nothing to disclose.
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