Digital Assessment of Three-Dimensional Spinopelvic Parameters in Female Lenke Type 1 Adolescent Idiopathic Scoliosis

Abstract

Study Design

Retrospective cross-sectional study.

Objectives

To investigate differences and correlations in multi-planar parameters across severity levels in female Lenke type 1 patients, and to identify key factors, thereby providing a basis for personalized preoperative planning.

Methods

Full-spine X-rays of 117 female Lenke type 1 patients (40 mild, 40 moderate, 37 severe; aged 10-18 years) were analyzed. Twelve spinopelvic parameters including Cobb angle, apical vertebral translation (AVT), apical vertebral rotation (AVR), thoracic kyphosis (TK), lumbar lordosis (LL), pelvic incidence (PI), sagittal vertical axis (SVA), and spinal tilt (ST) were measured using Mimics 21.0, followed by statistical analysis.

Results

Cobb angle, AVT, and AVR increased significantly with severity (P < 0.001). The severe group had greater SVA and smaller ST (P = 0.011; P = 0.038). Regression analysis identified AVT and AVR as significant predictors for moderate (OR = 1.314; OR = 42.094) and severe groups (OR = 1.470; OR = 241.351) (all P < 0.05). In mild and moderate groups, LL showed positive correlations with TK and PI (r = 0.380-0.591) and negative correlations with SVA (r = −0.558; r = −0.332). No significant correlations existed between LL and PI, TK, or SVA in the severe group.

Conclusions

In female Lenke type 1 patients, correcting AVT and AVR is a central surgical objective, as they are integral to coronal and transverse deformities, and AVR also drives sagittal imbalance. LL serves as a pivotal compensation parameter for sagittal balance in these patients. In mild and moderate patients, sagittal balance can be achieved through LL-centric compensation mechanisms. However, in severe patients, LL loses its compensatory role, necessitating surgical intervention to restore sagittal balance.

Keywords

adolescent idiopathic scoliosis Lenke 1 parametric measurements morphological studies

Introduction

Adolescent Idiopathic Scoliosis (AIS) is a spinal deformity of unknown origin occurring during adolescence, with a global prevalence of 1%-3%.¹ The current clinical gold standard for the clinical diagnosis of scoliosis is the measurement of the Cobb angle on standing posteroanterior radiographs.² This angle determines the severity classification of AIS, with a Cobb angle ≥40° indicating severe deformity necessitating surgical intervention, and lesser angles managed non-surgically.^3,4

AIS exhibits a pronounced gender disparity.⁵ Compared to males, females during the adolescent growth spurt – the period of most rapid spinal growth – are more susceptible to the effects of spinal biomechanical imbalance and hormonal fluctuations.⁶ This heightened susceptibility predisposes them to a greater risk of developing structural curves.⁷ Consequently, clinical management should prioritize female patients and incorporate individualized treatment strategies. Furthermore, as the spine functions as a three-dimensional integrated structure, the coronal, sagittal, and transverse planes are intrinsically interconnected. Analyzing the spine holistically from a 3D perspective enables a more comprehensive understanding of AIS.⁸ The Lenke classification is a categorization system for AIS based on curve type and location.⁹ By delineating the structural characteristics of major, minor, and compensatory curves, it facilitates precise therapeutic decision-making.¹⁰ In the surgical setting, this classification enables surgeons to preoperatively identify curves requiring correction, thereby preventing overly aggressive procedures while optimizing fusion level selection to minimize postoperative complications.¹¹ For non-operative management, it guides brace design to achieve individualized intervention.¹² Among female patients, Lenke type 1 is one of the most prevalent curve patterns.¹³ Lenke type 1 is characterized by a major main thoracic curve as the only structural curve, while the proximal thoracic and thoracolumbar/lumbar curves are non-structural.¹⁴ Analyzing the relationships among three-dimensional parameters in this specific subgroup offers a valuable approach to elucidate the mechanisms underlying spinal imbalance in female adolescents. However, there is currently a paucity of research focusing on the multiplanar spinal and pelvic parameters in female patients with Lenke 1.

Therefore, this study conducted an in-depth analysis of twelve coronal, transverse, and sagittal parameters to evaluate the spinal and pelvic alignment in female patients with Lenke type 1 curves. By performing a multidimensional and multiparametric assessment of their differences and correlations, we aimed to elucidate the interrelationships among these parameters across different anatomical planes, thereby providing valuable references for preoperative evaluation and surgical planning in this patient population.

Objects and Methods

Data Collection

This study collected 582 whole-spine X-ray images of adolescents aged 10-18 years from September 2023 to August 2024 at the Departments of Orthopedics and Radiology of the Affiliated Hospital of Inner Mongolia Medical University, the Second Affiliated Hospital of Inner Mongolia Medical University, and the First Hospital of Hohhot. After screening, 117 female cases that met the inclusion criteria were included in the study subjects (Figure 1). The research protocol was approved by the Medical Ethics Committee of Inner Mongolia Medical University (approval number: YKD2019138). Since this study utilized only existing medical data, neither involving identifiable subject information nor privacy, and posed no risks or harm to the subjects, informed consent was thus waived.

Figure 1.

Schematic Diagram of Data Source

Selection and Exclusion Criteria

Female patients aged 10-18 years were included based on the following criteria: a Cobb angle ≥10° measured on standing coronal radiographs, absence of scoliosis secondary to spinal trauma or other diseases, no other pathological spinal alterations, no prior treatment for spinal conditions, and confirmation as Lenke 1 AIS cases through clinical diagnosis by orthopedic specialists.

Inspection Equipment and Digital Measurement Software

Imaging equipment: Siemens DR (Multix Fusion, Germany) and Philips DR (DigitalDiagnost, Netherlands). Exposure parameters were standardized at a source-to-image distance of 200 cm, tube voltage of 120 kV, and tube current of 60 mA.

Full-spine standing coronal and sagittal radiographs were acquired using Philips DR and Siemens DR systems. Prior to imaging, participants were instructed to stand upright facing the detector, gazing straight ahead, with hips and knees fully extended, feet positioned shoulder-width apart, and elbows flexed at 90° with arms held horizontally across the chest. All participants underwent imaging using an identical positioning protocol, guaranteeing methodological consistency.

Digital measurement software: Mimics 21.0 (Mimics Research 21.0, Materialise, Belgium).

Method

Parameter Measurement Methods

1. Cobb angle: On a coronal X-ray image, it is the angle formed by lines drawn along the upper endplate of the upper-end vertebra and the lower endplate of the lower-end vertebra, or the angle formed by their perpendicular lines. (Figure 2A - Cobb).¹⁵

2. Apical Vertebral Translation (AVT):

When the C7 plumb line overlaps the sacral vertical line, AVT is the horizontal distance from the midpoint of the apical vertebra (or disc) of the scoliosis curve to the sacral vertical line.

When the C7 plumb line does not overlap the sacral vertical line, AVT for thoracic curves is the horizontal distance from the midpoint of the apical vertebra (or disc) to the C7 plumb line; for thoracolumbar and lumbar curves, it is the distance to the sacral vertical line (Figure 2A - AVT).¹⁶

3. Axial Vertebral Rotation (AVR): On an anteroposterior radiograph, it is graded using the Nash-Moe system based on the position of the convex pedicle shadow relative to the vertebral body margins. (Figure 2D).

Figure 2.

Schematic Diagram of Parameter Measurement. (A) Measurement of Cobb and Apical Vertebral Translation (AVT). (B) Measurement of Thoracic Kyphosis (TK), Lumbar Lordosis (LL), Pelvic Tilt (PT), Pelvic Incidence (PI) and Sacral Slope (SS). (C) Measurement of Sagittal Vertical Axis (SVA), Spinal Tilt (ST), Spinosacral Angle (SSA) and Spinopelvic Angle (SPA). (D) Measurement of Apical Vertebral Rotation (AVR).

Grade 0 (No rotation): The pedicles are symmetrically positioned within the vertebral body.

Grade I: The pedicle on the convex side migrates slightly towards the midline; the pedicle on the concave side overlaps the vertebral body margin.

Grade II: The pedicle on the convex side migrates approximately two-thirds of the distance towards the midline; the concave pedicle becomes nearly invisible.

Grade III: The concave pedicle is no longer visible; the convex pedicle reaches the midline.

Grade IV: The convex pedicle migrates beyond the midline.¹⁷

4. Thoracic Kyphosis (TK): Cobb angle between the upper endplate of T4 and the lower endplate of T12 (Figure 2B - TK).^18,19

5. Lumbar Lordosis (LL): Cobb angle between the upper endplate of L1 and the upper endplate of S1 (Figure 2B - LL).¹⁵

6. Pelvic Tilt (PT): The angle between the vertical line and the line connecting the midpoint of the S1 upper endplate to the center of the femoral heads (Figure 2B - PT).¹⁵

7. Pelvic Incidence (PI): The angle between the perpendicular line to the midpoint of the S1 upper endplate and the line connecting this midpoint to the center of the femoral heads (Figure 2B - PI).¹⁵

8. Sacral Slope (SS): The angle between the S1 upper endplate and the horizontal plane (Figure 2B - SS).¹⁵

9. Sagittal Vertical Axis (SVA): The vertical distance between the center of the C7 vertebral body and the posterosuperior corner of the sacrum. A plumb line anterior to the posterosuperior S1 endplate is considered positive; posterior is negative (Figure 2C - SVA).²⁰

10. Spinal Tilt (ST): The angle between the line connecting the center of C7 and the midpoint of the upper endplate of S1, and the horizontal line (Figure 2C - ST).²¹

11. Spinosacral Angle (SSA): The angle between the line connecting the center of C7 and the midpoint of the S1 upper endplate, and the S1 upper endplate itself (Figure 2C - SSA).²¹

12. Spinopelvic Angle (SPA): The angle formed by the line connecting the midpoint of the S1 upper endplate to the center of C7 and the line connecting the same S1 midpoint to the center of the femoral heads (Figure 2C - SPA).²¹

Measurement Schemes

All parameter measurements in this study were performed according to a unified and standardized measurement protocol. The measurements were divided into 2 groups: one group was measured under the guidance of the Chief Physician of the Spinal Surgery Department at Hospital A, and the other group was measured under the guidance of the Chief Physician of the Spinal Surgery Department at Hospital B. The values from these 2 measurements were then averaged. If a significant discrepancy existed between the 2 measurement values, a third measurement was conducted under the guidance of a third Chief Physician of Spinal Surgery. The average of the 3 measurements was then taken.

Relevance Criteria

Criteria for interpreting correlation coefficients: (1) When |r| = 1, it indicates a perfect correlation; (2) When 0 < |r| ≤ 0.4, it indicates a weak or slight correlation; (3) When 0.4 < |r| ≤ 0.6, it indicates a moderate correlation; (4) When 0.6 < |r| ≤ 0.8, it indicates a significant correlation; (5) When 0.8 < |r| < 1, it indicates a strong correlation.¹⁶

Statistical Analysis

Statistical analyses were performed using IBM SPSS Statistics 27.0.1 (SPSS Inc., USA). Differences in the above parameters were compared, and all measured parameters were subjected to correlation and regression analyses. For data with normal distribution and homogeneity of variance, results were expressed as mean ± standard deviation, and one-way ANOVA was used. For data not meeting normality or homogeneity assumptions, results were presented as median (lower quartile, upper quartile), and the Kruskal–Wallis H test was applied. Pairwise comparisons were conducted using the Jonckheere–Terpstra test. Pearson or Spearman correlation analyses were used to assess relationships between parameters. Multivariate logistic regression analysis was performed to identify influencing factors associated with different degrees of scoliosis. A P-value <0.05 was considered statistically significant.

Results

Overall Description of the Study Population

This study included 117 female patients with scoliosis, with a mean age of 14.58 ± 2.11 years. The Cobb angle averaged 30.4 ± 15.24° (range: 10.18°-84.89°). The distribution of lumbar modifiers was as follows: 76 cases were type A, 27 were type B, and 14 were type C. The classification of thoracic kyphosis showed 17 cases with hypokyphosis (−), 92 with normokyphosis (N), and 8 with hyperkyphosis (+) (Figure 3).

Figure 3.

Patient Basic Information.

Parameter Analysis Between Different Groups of Female Lenke Type 1 Patients

Comparison revealed statistically significant differences among the severity groups in female Lenke type 1 patients for the following parameters: Cobb angle、AVT、AVR、SVA and ST(H = 130.069, P < 0.001; H = 73.081, P < 0.001; H = 67.648, P < 0.001; H = 10.409, P = 0.005; H = 6.996, P = 0.030). No statistically significant differences were found for the remaining parameters (P > 0.05) (Table 1).

Table 1.

Parameter Analysis Between Different Groups of Female Lenke Type 1 Patients

	Mild scoliosis group(n = 40)	Moderate scoliosis group(n = 40)	Severe scoliosis group(n = 37)	F/H	P
Age(yr)	14.5(13-16)	15(14-17)	13(12-16)	5.877	0.053
Cobb(°)	16.17(13.8-17.89)	26.53(23.38-32)	46.48(43.22-53.96)	130.069	<0.01
AVT(mm)	14.79(10.47-19.45)	28.23(22.45-32.48)	38.22(31.8-45.88)	73.081	<0.01
AVR	0(0-Ⅰ)	Ⅰ(Ⅰ-Ⅱ)	Ⅱ(Ⅱ-Ⅱ)	67.648	<0.01
TK(°)	24.89(17.65-33.1)	25.3(17.57-33.57)	19.31(14.25-31.15)	1.045	0.593
LL(°)	25.19 ± 10.69	25.96 ± 11.66	24.01 ± 12.96	1.361	0.263
PT(°)	10.15 ± 6.28	10.24 ± 6.84	11.37 ± 7.12	0.383	0.683
PI(°)	45.87 ± 10.7	47.38 ± 9.78	48.7 ± 10.85	0.706	0.496
SS(°)	37.45 ± 8.78	37.96 ± 7.23	37.95 ± 7.33	0.054	0.947
SVA(mm)	2.61(−21.76-17)	−8.67(−22.91-17.48)	17.98(−2.53-32.62)	10.409	0.005
ST(°)	91.53(89.74-94.44)	92.35(90-94.55)	90(87.38-92.76)	6.996	0.030
SSA(°)	129.34 ± 10.02	130.28 ± 7.63	128.39 ± 8.24	0.454	0.637
SPA(°)	172.65(165.02-175.23)	172.03(168.38-176.65)	168.98(163.1-176.34)	0.959	0.619

AVT, apical vertebral translation; AVR, apical vertebra rotation; TK, thoracic kyphosis; LL, lumbar lordosis; PT, pelvic tilt; PI, pelvic incidence; SS, sacral slope; SVA, sagittal vertical axis; ST, spinal tilt; SSA, spinosacral angle; SPA, spinopelvic angle.

Jonckheere-Terpstra Trend Test Analysis of Parameters Between Different Groups in Female Lenke Type 1 Patients

Cobb angle, AVT, and AVR increased progressively with the severity of the condition (P < 0.001). The SVA in the severe group was significantly greater than that in the mild and moderate groups (P = 0.011), whereas the ST was significantly lower (P = 0.038), as detailed in Table 2 and Figure 4A–E.

Table 2.

Jonckheere-Terpstra Trend Test of Parameters Between Different Groups in Female Lenke Type 1 Patients

Parameter	JT	P	Patterns of change	Significant change intervals
Cobb(°)	4560.0	0.000	Monotonic increase	Mild vs Moderate P < 0.01 Moderate vs Severe P < 0.01
AVT(mm)	4096.0	0.000	Monotonic increase	Mild vs Moderate P < 0.01 Moderate vs Severe P < 0.01
AVR(°)	3874.5	0.000	Monotonic increase	Mild vs Moderate P < 0.01 Moderate vs Severe P < 0.01
SVA(mm)	2791.0	0.011	Increase in severe	Mild vs Severe P = 0.005 Moderate vs Severe P = 0.001
ST(°)	1865.5	0.038	Decrease in severe	Mild vs Severe P = 0.016 Moderate vs Severe P = 0.008

AVT, apical vertebral translation; AVR, apical vertebra rotation; SVA, sagittal vertical axis; ST, spinal tilt.

Figure 4.

Jonckheere-Terpstra Trend Test of Parameters Between Different Groups in Female Lenke Type 1 Patients. AVT: Apical Vertebral Translation, AVR: Apical Vertebra Rotation, SVA: Sagittal Vertical Axis, ST: Spinal Tilt.

Correlation Analysis of Coronal, Transverse and Sagittal Parameters in the Mild Scoliosis Group of Female Lenke Type 1 Patients

In the mild group, significant correlations were observed among several anatomical parameters. Specifically, Cobb angle, AVT, and AVR were all positively correlated with one another (Cobb vs AVT: r = 0.815, P < 0.001; Cobb vs AVR: r = 0.338, P = 0.033; AVT vs AVR: r = 0.362, P = 0.022). Additionally, TK showed a weak positive correlation with LL (r = 0.380, P = 0.016) and a weak negative correlation with SVA (r = −0.355, P = 0.025). Furthermore, LL was significantly correlated with multiple parameters: it demonstrated moderate positive correlations with PI and ST (r = 0.591, P < 0.001; r = 0.544, P < 0.001), high positive correlations with SS and SSA (r = 0.822, P < 0.001; r = 0.897, P < 0.001), and a moderate negative correlation with SVA (r = −0.558, P < 0.001), as detailed in Table 3.

Table 3.

Correlation Between Coronal, Transverse and Sagittal Parameters in the Mild Scoliosis Group of Female Lenke Type 1 Patients

Classification	Parameter	r	P
Coronal vs Coronal	Cobb vs AVT	0.815	<0.001
Coronal vs Transverse	Cobb vs AVR	0.338	0.033
Coronal vs Transverse	AVT vs AVR	0.362	0.022
Sagittal vs Sagittal	TK vs LL	0.380	0.016
	TK vs SVA	−0.355	0.025
	LL vs PI	0.591	<0.001
	LL vs SS	0.822	<0.001
	LL vs SVA	−0.558	<0.001
	LL vs ST	0.544	<0.001
	LL vs SSA	0.897	<0.001
	PT vs PI	0.563	<0.001
	PT vs SPA	−0.724	<0.001
	PI vs SS	0.639	<0.001
	PI vs SSA	0.626	<0.001
	SS vs SSA	0.932	<0.001
	SVA vs ST	−0.819	<0.001
	SVA vs SSA	−0.479	0.002
	SVA vs SPA	−0.337	0.033
	ST vs SSA	0.578	<0.001
	ST vs SPA	0.408	0.009

Correlation Analysis of Coronal, Transverse and Sagittal Parameters in the Moderate Scoliosis Group of Female Lenke Type 1 Patients

In the moderate group, significant correlations were observed among several anatomical parameters. Specifically, Cobb angle showed a strong positive correlation with AVT and a moderate positive correlation with AVR (r = 0.702, P < 0.001; r = 0.407, P < 0.001). Additionally, TK demonstrated a moderate positive correlation with LL (r = 0.487, P = 0.001). Furthermore, LL was significantly correlated with multiple parameters: it exhibited a moderate positive correlation with PI (r = 0.417, P = 0.007), a strong positive correlation with SS (r = 0.749, P < 0.001), a weak negative correlation with SVA (r = −0.332, P = 0.036), and a very strong positive correlation with SSA (r = 0.846, P < 0.001), as detailed in Table 4.

Table 4.

Correlation Between Coronal, Transverse and Sagittal Parameters in the Moderate Scoliosis Group of Female Lenke Type 1 Patients

Classification	Parameter	r	P
Coronal vs Coronal	Cobb vs AVT	0.702	<0.001
Coronal vs Transverse	Cobb vs AVR	0.407	0.009
Sagittal vs Sagittal	TK vs LL	0.487	0.001
	LL vs PI	0.417	0.007
	LL vs SS	0.749	<0.001
	LL vs SVA	−0.332	0.036
	LL vs SSA	0.846	<0.001
	PT vs PI	0.627	<0.001
	PT vs SPA	−0.768	<0.001
	PI vs SS	0.626	<0.001
	PI vs SSA	0.559	<0.001
	SS vs SSA	0.887	<0.001
	SVA vs ST	−0.801	<0.001
	SVA vs SSA	−0.367	0.020
	SSA vs SPA	0.323	0.042

Correlation Analysis of Coronal, Transverse and Sagittal Parameters in the Severe Scoliosis Group of Female Lenke Type 1 Patients

In the severe group, significant correlations were observed among several anatomical parameters. Specifically, Cobb angle, AVT, and AVR were all positively correlated with one another (Cobb vs AVT: r = 0.761, P < 0.001; Cobb vs AVR: r = 0.453, P = 0.005; AVT vs AVR: r = 0.454, P = 0.005). In contrast, the correlations of LL with PI, TK, ST, and SVA were not statistically significant, as detailed in Table 5.

Table 5.

Correlation Between Coronal, Transverse and Sagittal Parameters in the Severe Scoliosis Group of Female Lenke Type 1 Patients

Classification	Parameter	r	P
Coronal vs Coronal	Cobb vs AVT	0.761	<0.001
Coronal vs Transverse	Cobb vs AVR	0.453	0.005
Coronal vs Transverse	AVT vs AVR	0.454	0.005
Sagittal vs Sagittal	LL vs PT	−0.419	0.010
	LL vs SS	0.553	<0.001
	LL vs SSA	0.749	<0.001
	LL vs SPA	0.456	0.005
	PT vs PI	0.681	<0.001
	PT vs SPA	−0.831	<0.001
	PI vs SS	0.661	<0.001
	PI vs ST	−0.348	0.035
	PI vs SSA	0.452	0.005
	PI vs SPA	−0.520	<0.001
	SS vs SSA	0.844	<0.001
	SVA vs ST	−0.898	<0.001
	SVA vs SPA	−0.470	0.003
	ST vs SPA	0.524	<0.001

AVT, apical vertebral translation; AVR, apical vertebra rotation; LL, lumbar lordosis; PT, pelvic tilt; PI, pelvic incidence; SS, sacral slope; SVA, sagittal vertical axis; ST, spinal tilt; SSA, spinosacral angle; SPA, spinopelvic angle.

Correlation Analysis of Overall Coronal, Transverse and Sagittal Parameters in Female Lenke Type 1 Patients

In the overall group of female Lenke type 1 patients, significant correlations were observed among several anatomical parameters. Specifically, Cobb angle, AVT, and AVR were all positively correlated with one another (Cobb vs AVT: r = 0.803, P < 0.001; Cobb vs AVR: r = 0.803, P < 0.001; AVT vs AVR: r = 0.705, P < 0.001). Additionally, AVR showed weak negative correlations with LL and ST (r = −0.187, P = 0.043; r = −0.216, P = 0.019). Furthermore, TK showed a weak positive correlation with LL and a weak negative correlation with SVA (r = 0.400, P < 0.001; r = −0.190, P = 0.040). Finally, LL was significantly correlated with multiple parameters: it demonstrated weak positive correlations with PI, ST, and SPA (r = 0.344, P < 0.001; r = 0.391, P < 0.001; r = 0.266, P = 0.004), a strong positive correlation with SS (r = 0.726, P < 0.001), a moderate negative correlation with SVA (r = −0.430, P < 0.001), and a very strong positive correlation with SSA (r = 0.843, P < 0.001), as detailed in Table 6.

Table 6.

Correlation Between Coronal, Transverse and Sagittal Parameters in Female Lenke Type 1 Patients

Classification	Parameter	r	P
Coronal vs Coronal	Cobb vs AVT	0.803	<0.001
Coronal vs Transverse	Cobb vs AVR	0.803	<0.001
Coronal vs Transverse	AVT vs AVR	0.705	<0.001
Coronal vs Sagittal	Cobb vs SVA	0.223	0.016
	AVT vs SVA	0.223	0.016
	AVT vs ST	−0.196	0.034
Transverse vs Sagittal	AVR vs LL	−0.187	0.043
	AVR vs SVA	0.260	0.005
	AVR vs ST	−0.216	0.019
Sagittal vs Sagittal	TK vs LL	0.400	<0.001
	TK vs SVA	−0.190	0.040
	LL vs PI	0.344	<0.001
	LL vs SS	0.726	<0.001
	LL vs SVA	−0.430	<0.001
	LL vs ST	0.391	<0.001
	LL vs SSA	0.843	<0.001
	LL vs SPA	0.266	0.004
	PT vs PI	0.593	<0.001
	PT vs SPA	−0.793	<0.001
	PI vs SS	0.632	<0.001
	PI vs SSA	0.520	<0.001
	PI vs SPA	−0.394	<0.001
	SS vs SSA	0.884	<0.001
	SVA vs ST	−0.866	<0.001
	SVA vs SSA	−0.411	<0.001
	SVA vs SPA	−0.346	<0.001
	ST vs SSA	0.421	<0.001
	ST vs SPA	0.402	<0.001
	SSA vs SPA	0.274	0.003

Influencing Factors of Different Severity in Female Lenke Type 1 Patients

Multivariable logistic regression identified AVT and AVR as significant factors distinguishing the moderate and severe groups from the mild group. Notably, the impact of AVR was markedly greater than that of AVT, as evidenced by its significantly higher OR values, as detailed in Table 7.

Table 7.

Multivariate Logistic Regression Analysis was Performed to Analyze the Influencing Factors of Different Severity

Classification	Variable	β	SE	waldX ²	P	OR	95%CI
Moderate scoliosis group	Intercept	−25.344	27.714	0.836	0.360	-	-
	AVT	0.273	0.074	13.560	<0.01	1.314	1.136-1.520
	AVR	3.740	1.231	9.225	0.002	42.094	3.768-470.264
	SVA	0.009	0.036	0.064	0.800	1.009	0.941-1.082
	ST	0.176	0.298	0.348	0.555	1.192	0.665-2.139
Severe scoliosis group	Intercept	−27.143	30.373	0.799	0.372	-	-
	AVT	0.385	0.084	21.214	<0.01	1.470	1.248-1.732
	AVR	5.486	1.374	15.951	<0.01	241.351	16.345-3563.780
	SVA	0.009	0.039	0.054	0.817	1.009	0.930-1.090
	ST	0.125	0.328	0.144	0.704	1.133	0.595-2.155

Compared with adolescents with mild scoliosis group.

AVT, apical vertebral translation; AVR, apical vertebra rotation; SVA, sagittal vertical axis; ST, spinal tilt.

Discussion

The incidence of AIS has been rising in recent years.²² Given its significant impact on the physical and psychological well-being of adolescents, timely diagnosis and treatment are critically important for affected individuals.^23,24 The Lenke classification system plays a vital role in guiding AIS treatment, with Lenke type 1 being the most prevalent, accounting for approximately 50% of cases.²⁵ However, previous studies on Lenke type 1 predominantly focused on changes in coronal plane parameters (eg, Cobb angle) and selected sagittal plane parameters (eg, TK, LL) between preoperative and postoperative states.^26,27 These studies often did not incorporate transverse plane spinal parameters (eg, AVR) and overlooked potential differences across the varying severity levels. Furthermore, studies have found that the incidence and severity of AIS are significantly higher in female patients compared to males.^5,9 Therefore, this study utilized Mimics 21.0 to quantify anatomical parameters in female patients with Lenke type 1 AIS. It aimed to analyze differences and correlations in coronal, transverse, and sagittal spinal-pelvic parameters across varying severity levels, thereby providing clinically relevant references for improved patient management.

In the coronal plane, a normal spine exhibits a nearly vertical alignment, characterized by a high degree of symmetry and stability.²⁸ The onset of scoliosis is initially marked by coronal plane bending and vertebral deviation from the midline, disrupting this inherent symmetry.²⁹ Studies by Liu et al.¹⁶ and Wu¹⁵ showed that the main curve Cobb angle and AVT differ among various types of scoliosis in AIS patients. However, these studies were conducted in general AIS populations and did not focus specifically on particular Lenke subtypes or female patients. This study demonstrates that in female Lenke type 1 patients, the Cobb angle, AVT, and AVR exhibit a significant and synchronous increasing trend with disease progression (P < 0.001). This finding not only corroborates the conclusions of Liu et al.¹⁶ and Wu¹⁵ but is further validated specifically within the distinct cohort of female Lenke type 1 patients. Previous studies reported a strong positive correlation between the coronal Cobb angle and both AVT and AVR in scoliosis.^15,30-32 This study further revealed strong positive correlations among the coronal Cobb angle, AVT, and AVR in female Lenke type 1 patients (r = 0.893, P < 0.001; r = 0.803, P < 0.001; r = 0.705, P < 0.001). These findings suggest that spinal deformities in the coronal and transverse planes do not exhibit a unidirectional relationship as indicated by previous studies,^15,30-32 but rather function as an interdependent pathological entity. Baghdadi and Baldwin³³ found that the ratio of thoracic to lumbar AVT and AVR is one of the key factors determining the suitability of selective thoracic fusion for Lenke 1C patients. Furthermore, this study found that AVT and AVR are clinically significant in non-1C female Lenke type 1 patients. The multiple regression analysis for female Lenke type 1 patients indicated that, compared to the mild scoliosis group, both AVT and AVR were identified as factors associated with severity in the moderate and severe groups, with the influence of AVR being more pronounced. Schwab et al.³⁴ proposed that when sagittal spinal imbalance occurs, the body can compensate through pelvic tilt to maintain an upright posture, indicating the existence of an interactive compensatory mechanism between the spine and pelvis. This study further revealed that in female Lenke type 1 patients, AVR negatively correlated with LL and positively correlated with SVA (r = −0.187, P = 0.043; r = 0.260, P = 0.005). This suggests that with the aggravation of vertebral rotation, the physiological curve of the lumbar spine decreases, and the body leans forward to disrupt the sagittal balance. This suggests AVR may be a key factor in the compensatory mechanism. Consequently, in the surgical planning for female Lenke type 1 patients, the correction of AVT and AVR should be a central objective. These parameters are not only integral components of the coronal and transverse plane deformities, but AVR also contributes to the development of sagittal imbalance.

The goal of AIS surgery is to correct the Cobb angle and restore trunk balance in both the coronal and sagittal planes.³⁵ Adequate restoration of sagittal alignment is essential for minimizing postoperative complications.^33,36 Therefore, analyzing sagittal balance parameters in severe female patients with Lenke type 1 can provide an important reference for formulating surgical plans. SVA is a crucial parameter for assessing sagittal balance, and ST reflects the overall tilt of the spine in the sagittal plane.²¹ This study found that SVA was significantly increased in the severe group (Mild vs Severe: P = 0.005; Moderate vs Severe: P = 0.001), whereas ST was significantly reduced (Mild vs Severe: P = 0.016; Moderate vs Severe: P = 0.008), indicating that sagittal imbalance in these patients primarily manifests as an anterior displacement of the body’s center of gravity and a forward inclination of the spine. Consequently, SVA and ST may serve as important indicators for assessing sagittal imbalance in female patients with Lenke type 1 preoperatively. However, in multiple regression analysis, neither SVA nor ST showed statistical significance, which suggests that their alterations are likely secondary to the increased curve severity, rather than acting as independent predictors of deformity severity.

The spine and pelvis are not independent anatomical structures but form an integrated functional unit that synergistically maintains sagittal balance. Alterations in one segment can induce compensatory changes in adjacent spinal or pelvic regions.³⁷ Studies by Lin et al.³⁸ and Ma et al.³⁹ found positive correlations between LL and PI, SS, and TK in AIS patients. The results for these parameters in the mild and moderate groups of this study align with previous findings.^38,39 Additionally, this study found that LL was negatively correlated with SVA in the mild and moderate groups (r = −0.558, P < 0.001; r = −0.332, P = 0.036), suggesting that as SVA decreases (indicating posterior shift), LL increases accordingly. Given the positive correlation between LL and SS (r = 0.822, P < 0.001; r = 0.749, P < 0.001), the sacrum tilts to facilitate pelvic anteversion, thereby aiding in restoring overall spinal stability. However, in the severe group, no statistically significant correlations were found between LL and PI, TK, ST, or SVA. This indicates that LL can no longer serve an effective compensatory role at this stage, suggesting that clinical intervention may be considered to restore sagittal alignment. Furthermore, the postoperative restoration of LL can serve as a key indicator for assessing therapeutic efficacy. In summary, although female patients with Lenke type 1 primarily manifest a main thoracic curve, the lumbar spine and pelvis can utilize compensatory mechanisms to maintain overall body balance. Although a study proposed PI as the core regulator of sagittal compensation in AIS,^40,41 our research further indicate that LL may be a key parameter in this compensatory mechanism. In female patients with Lenke type 1 AIS, LL facilitates the restoration of global spinal-pelvic alignment by modulating the spatial relationship between the thoracic spine and pelvis. Building on this,^40,41 our study delineates a novel finding: in mild to moderate patients, sagittal balance is achieved by increasing LL to reduce SVA and adjust pelvic position. However, in severe patients, the compensatory capacity of the lumbar spine reaches its limit, and the natural compensatory mechanisms of the spinopelvic system can no longer effectively maintain overall balance. Consequently, surgical intervention becomes the necessary approach to restore physiological spinal curvature and global sagittal balance. This understanding also provides new insights into the progression toward a decompensated state.

This study has several limitations. Firstly, as a cross-sectional investigation, its findings can only reveal associations among parameters and preclude causal inferences or prognostic conclusions. Future prospective cohort studies are needed to establish more definitive evidence. Secondly, the analysis of transverse plane parameters was limited to AVR, which was quantified exclusively via the Nash-Moe method. Subsequent investigations will aim to include additional transverse parameters and perform measurements with greater precision using modalities like CT and EOS. Finally, the present cohort consisted exclusively of female patients from the Inner Mongolia region of China. Future studies will expand the sample to include male patients and individuals from more diverse geographical origins.

Conclusion

Footnotes

ORCID iD

Ruofan Zhang

Ethical Considerations

The research protocol was approved by the Medical Ethics Committee of Inner Mongolia Medical University (approval number: YKD2019138).

Consent to Participate

Since this study utilized only existing medical data, neither involving identifiable subject information nor privacy, and posed no risks or harm to the subjects, informed consent was thus waived.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Inner Mongolia Autonomous Region “Grassland Talents” Project Youth Innovation and Entrepreneurship Talent Project (2020). 2021 Inner Mongolia Autonomous Region Mongolian Medicine Collaborative Innovation Center Scientific Research Project (MYYXTYB202104). Key Research Project of Inner Mongolia Medical University in 2021 (YKD2021ZD001). Inner Mongolia Department of Education Higher Education Innovation Team Development Plan (NMGIRT2227). The 2022 “Grassland Talent” Project. Inner Mongolia Autonomous Region Key Research and Development and Achievement Transformation Plan in 2023 (Science and Technology to Support Ecological Protection and high-quality Development in the Yellow River Basin) Project (2023YFHH0003).

Declaration of Conflicting Interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

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