The effect of coronal plane correction on the sagittal plane in adolescent idiopathic scoliosis patients

Aim:This study will investigate the effect of correction achieved by surgical intervention in the coronal plane on the sagittal plane in the posterative follow-up of patients with Adolescent Idiopathic Scoliosis (AIS). Materials and Methods: 25 patients with adolescent idiopathic scoliosis who underwent surgery by us were included. Preoperatively, the following measurements were taken in the coronal plane: cranial tilt, cervical tilt, sagittal vertical axis, sacral slope, pelvic tilt, pelvic incidence, T2-T5 kyphosis angle, T5-T12 kyphosis angle, T2-T12 kyphosis angle, T10-L2 angle, cervical lordosis, L1-S1 lordosis, L1-L3 lumbar lordosis, L4-S1 lumbar lordosis, lumbosacral take-off angle, t1-pa pelvis angle, shoulder height, C0-C2, and C2-C7 ,C0-7 vertebral measurements. Apical vertebra, sagittal stable vertebra, and coronal stable vertebra were determined. Lenke classification and Risser staging were used. Ameliyat öncesierative coronal curvature and Ameliyat sonrasıerative curvature degrees were measured, and the correction percentage was calculated. Correction, Ameliyat sonrasıerative coronal plane correction loss, and percentage were also calculated in the 6th month and 1st-year graphs. The effect of coronal plane correction on cranial tilt, cervical tilt, sagittal vertical axis, sacral slope, pelvic tilt, pelvic incidence, T2-T5 kyphosis angle, T5-T12 kyphosis angle, T2-T12 kyphosis angle, T10-L2 angle, cervical lordosis, L1-L5 lordosis, L1-L3 lumbar lordosis, L4-S1 lumbar lordosis, lumbosacral take-off angle, t1-pa pelvis angle, shoulder height, C0-C2, and C2-C7,C0-7 vertebral angles, coronal and sagittal stable vertebra, and apical vertebra will be investigated in posterative, 6th-month, and 1-year graphs. Measurements will be taken from posterative, 6th-month, and 12th-month graphs. Results: 1. Coronal Plane Correction is Effective and Durable: The preoperative Cobb angle of 46.48° decreased to 12.71° in the early postoperative period and further to 11.61° at the 1-year follow-up; the correction rate reached 75%. This correction was statistically significant and maintained over the 1-year observation period. 2. Thoracic Kyphosis (T2–T12) Increased Significantly: The mean kyphosis angle increased from 26.90° preoperatively to 38.73° at the 1-year follow-up, with a net mean gain of ~11.8°. Segmental analysis revealed that this increase originated particularly from the upper thoracic segment. This gain is consistent with kyphosis increase values reported in the literature. 3. Lumbar Lordosis (L1–S1) Increase is Proximal Segment Dominant: An average increase of 9.5° was observed in global lumbar lordosis, and this increase was statistically significant. The most notable gain occurred in the L1–L3 segment, with an average increase of +11.5°. Changes in the lower lumbar segment (L4–S1) remained more minimal. 4. Thoracolumbar Junction Angle (T10–L2) Showed a Slight Increase but was Not Significant: The average increase was ~5.8°, but statistical significance was not reached when comparing preoperative values with those at 6 months and 1 year (p > 0.05). 5. A Gradual Improvement Trend was Observed in Cervical Lordosis and Tilt Parameters: The C0–C7 lordosis angle increased from 25.05° preoperatively to 31.01° at the 1-year follow-up, and this increase approached statistical significance (p=0.09). A significant difference was found in lower cervical lordosis (C2–C7) with a gain of ~+6.5° (p<0.05). Changes in cranial tilt and cervical tilt remained more limited. 6. Pelvic and Global Sagittal Balance Parameters Did Not Show Significant Changes: Pelvic tilt, pelvic incidence, sacral slope, and T1–pelvis angles did not change to a biologically significant extent in the postoperative period. No significant difference was found in parameters other than the lumbosacral take-off angle. This finding reflects the anatomical stability and compensatory role of these angles. 7. A Significant Correlation was Found Between Cobb Correction Percentage and Sagittal Gains: The highest correlation was observed between lumbar lordosis and the Cobb correction percentage (ρ = +0.51, p < 0.001). A positive correlation was similarly found with thoracic kyphosis (ρ = +0.42, p = 0.02), but no significant relationship was found with pelvic parameters. 8. Regression Analyses Confirmed the Effect of 1% Cobb Correction on Sagittal Angles: Each 1% correction in Cobb was associated with a +0.62° increase in lumbar lordosis and a +0.31° increase in thoracic kyphosis. These effects were statistically significant and demonstrate the contribution of Cobb correction to the reconstruction of the sagittal contour. 9. ROC Analyses Revealed Limited Predictive Power of Coronal Correction for ≥10° Sagittal Gain: The AUC was 0.63 for thoracic kyphosis and 0.62 for lumbar lordosis, indicating limited success in predicting these gains based on the Cobb correction percentage. Although the Cobb correction percentage showed a biologically significant trend in predicting these targets, its sensitivity and specificity were found to be low. According to the Youden index, the optimal cutoff values were calculated as 68.8% for thoracic kyphosis and 57.7% for lumbar lordosis. These findings demonstrate that coronal correction in the surgery of adolescent idiopathic scoliosis patients has a significant impact on the sagittal plane at both segmental and global levels. The obtained data highlight the necessity of not neglecting the sagittal profile and the need to consider kyphosis and lordosis parameters as active targets in surgical planning.