Global and segmental thoracolumbar sagittal alignment in adolescent idiopathic scoliosis compared to normal individuals

Objective: To quantify differences of global and segmental sagittal thoracolumbar alignment between normal individuals and adolescent idiopathic scoliosis (AIS) according to primary curve types. Methods: Radiographic parameters were compared between 1115 normal adolescents and young adults versus 1779 AIS. Thoracic kyphosis (T1-T12), lumbar lordosis (L1-S1), segmental alignment (T1-T5, T5-T10), thoracolumbar junction (T10-L1), segmental lordosis (L1-L4, L4-S1), lumbar and thoracic apex, thoracolumbar inflection point, global alignment parameters (SVA C7, SVA C2, OD-HA, TPA, GT, SSA) and pelvic parameters (PI, PT, SS) were measured. Results: C2 and C7 SVA was smaller and more posteriorly located in AIS compared to normal. Primary thoracic curves (Lenke 1, 2 and 3) had the lowest TK at T5-T10 compared to normal and primary thoracolumbar curves (Lenke 5 and 6). The thoracolumbar junction T10-L1 was smallest and slightly lordotic in Lenke 1 and 2. Distal lordosis L4-S1 and PI were highest in thoracolumbar curves (Lenke 3, 5 and 6). Thoracolumbar inflexion points, thoracic and lumbar apex were located more cranial in thoracic curves (Lenke 1 and 2) compared to normal and other AIS types. Conclusion: Thoracic curves (Lenke 1 and 2) were hypokyphotic in the distal thoracic segment T5-T10, had a neutral thoracolumbar junction T10-L1 and their apex and thoracolumbar junction were more cranial. Lenke 3 curves had an increased lordosis in the distal lumbar segment L4-S1. Primary lumbar curves (Lenke 5 and 6) had a higher PI and distal lordosis L4-S1, and the highest C7 SVA.