Spine - 2026-08-19 - Journal Article
Sagittal Alignment Differences Between Normal Subjects and Adolescent Idiopathic Scoliosis Using Vertebral Pelvic Angles.
Aleman C, Goetsch T, Hills J, Kelly MP, Battesti G, Chomienne L, Ilharreborde B, Finoco M, Ferrero E, Khalifé M, Odent T, de Charnacé E, Prost S, Blondel B, Solla F, Ould-Slimane M, Pesenti S, Charles YP
Topics
Key Takeaway
In primary thoracic AIS (Lenke 1–3), thoracic kyphosis T1–T12 is reduced by >8° and L1PA is elevated by >3° compared to normals, yet the global T4-to-hip axis remains preserved, supporting vertebropelvic angles as surgical alignment targets.
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Summary
This multicenter registry study compared sagittal spinopelvic alignment between 1,115 normal subjects and 1,779 AIS patients aged 10–30 years using vertebropelvic angles (T4PA, L1PA) and thoracolumbar inflection point (TIP) position. Lenke 1–3 curves demonstrated reduced TK T1–T12 (<8°, p<0.001), reduced TK T10–L1 (<5°, p<0.001), and increased LL L1–L4 (>3°, p<0.001) and L1PA (>3°, p<0.001) versus normals, while the global T4-to-hip axis was preserved across all Lenke types. L1PA correlated strongly with PI (r>0.7) and T4PA (r>0.9), and TIP position significantly modulated T4PA–L1PA differences (cranial TIP: negative difference; caudal TIP: positive difference; p<0.001), with predictive formulae achieving R²>0.6.
Key Limitation
The cross-sectional design cannot establish whether the observed sagittal alignment differences in AIS are causative, compensatory, or incidental to the primary coronal deformity, limiting mechanistic interpretation.
Original Abstract
STUDY DESIGN
Retrospective multicenter registry study.
OBJECTIVE
To compare sagittal spinopelvic alignment between normal subjects and Adolescent Idiopathic Scoliosis (AIS), to evaluate the relationship between T4 and L1 Pelvic Angles (T4PA-L1PA), including the influence of Thoracolumbar Inflection Point (TIP).
SUMMARY OF BACKGROUND DATA
Vertebropelvic angles were described as alignment targets for normal adults, but their role remains incompletely defined in younger AIS patients.
METHODS
Full-spine radiographs of 1115 normal subjects and 1779 AIS patients (10-30 y) were analyzed. AIS was classified according to Lenke. Measurements included Pelvic Incidence (PI), Pelvic Tilt (PT), segmental Thoracic Kyphosis (TK) and Lumbar Lordosis (LL), T4PA, L1PA. A Pearson correlation analyzed the relationship between parameters. TIP was categorized as cranial (above T12), junctional (T12-L1), or caudal (below L1), and T4PA-L1PA analyzed according to TIP (ANOVA). Formulae LL=0.5×PI-21 and L1PA=1.4×PI-1.7×L1PA-2 were evaluated using linear regression.
RESULTS
TK T1-12 was smaller <8° (P<0.001), T10-L1 <5° (P<0.001) in Lenke 1, 2 and 3 compared to normal. LL L1-L4 was larger >3° (P<0.001) in Lenke 1. L1PA differences >3° (P<0.001) existed in Lenke 1 and 2. A correlation existed between L1PA and PI (r>0.7), L1PA and PT (r>0.7), L1PA and T4PA (r>0.9) for normal and each Lenke type. T4PA-L1PA differences increased from negative to positive as the TIP moved from cranial to caudal in normal and AIS (P<0.001). Formulae for L1PA and LL calculation showed good agreement with measured values (R²>0.6).
CONCLUSION
Primary thoracic AIS had smaller TK T1-T12, TK T10-L1 and larger LL L1-L4, L1PA, while the T4-L1hip axis remained globally preserved in normal and AIS. The TIP influenced segmental alignment, with larger L1PA and smaller (negative) T4PA-L1PA differences. Vertebropelvic angles provide a reliable target for surgical planning in AIS.