Thoracolumbar Biomechanical Analysis of Lenke Type 1 Adolescent Idiopathic Scoliosis Across Roussouly Classifications

Lenke type 1 is the most common adolescent idiopathic scoliosis (AIS), and its sagittal morphology critically influences progression and treatment. However, its biomechanical characteristics across Roussouly types remain unclear.

To quantify the biomechanical responses of Lenke type 1 AIS under pure bending moments across different Roussouly classifications.

This study was based on a validated thoracolumbar finite element model. Using mesh morphing, spinal alignments and vertebral rotations were adjusted to construct finite element models of Lenke type 1 AIS with Roussouly types 1-4. Simulations were conducted under ±7.5 Nm pure bending moments for flexion-extension, lateral bending, and axial rotation. Spinal range of motion (ROM) and intervertebral disc loadings-including force, moment, and Von Mises stress-were quantified.

Compared to the normal model, the AIS model showed asymmetrical total ROM at the T7-T12 segment, whereas the T1-S1 segment remained relatively symmetrical. At the T9-T10 and T12-L1 discs, shear and compressive forces increased markedly, with peak values of 197 N and secondary moments reaching ~2.8 Nm. Stress in the T9-T10 disc exhibited a distinct concave-side concentration, with the maximum Von Mises stress reaching 7.7 MPa. The T1-S1 ROM during extension, right bending, and right rotation in Roussouly 1 and 2 was ~10% greater than in Roussouly 3 and 4, with markedly higher shear and compressive forces (up to 50-fold) at the T6-T7 and T9-T10 discs. Regarding stress distribution, Von Mises stress at the T6-T7 and T9-T10 discs was higher in Roussouly 3 and 4, whereas stress at the T12-L1 disc was more pronounced in Roussouly 1 and 2.

The findings underscore the critical role of sagittal morphology in AIS biomechanics. Compared to Roussouly 1 and 2, Roussouly 3 and 4 exhibited reduced ROM, lower disc forces, and more favorable stress distributions, suggesting a biomechanically advantageous load-bearing pattern.