Purpose One of the downsides of spinal correction surgery for adolescent idiopathic scoliosis (AIS) is the cessation of spinal longitudinal growth within the fused levels in growing children. However, the surgery itself has the potential to increase spinal longitudinal length by correcting the curvature. The purpose of this study was to evaluate the correlation between curve correction and increased spinal longitudinal length by corrective surgery for AIS. Methods This study included 208 consecutive patients (14 male, 194 female) with AIS who underwent posterior or anterior correction and fusion surgeries. Mean age at the time of surgery was 15.7 ± 3.3 years (range 10-20 years). Patients with hyperkyphosis of more than 40° were excluded. All patients had main curves in the thoracic spine (Lenke type 1 or 2). Forty-three patients underwent anterior spinal correction and fusion (ASF) and 164 underwent posterior spinal correction and fusion (PSF). The mean preoperative height was 154.7 ± 6.9 cm (range 133-173 cm). Pre and postoperative PA standing X-ray films were used to measure the Cobb angle and spinal length between the end vertebrae of the main thoracic curve, and between T1 and L5. The patients were divided into ASF and PSF groups, within which correlations between the Cobb angle correction and spinal length increase were evaluated. Results In the ASF group, the mean preoperative Cobb angle of the main thoracic curve was 54.9 ± 8.3° (range 41-83°) and it was corrected to 19.7 ± 9.5° (range 0-47°) with a mean correction of 35.2 ± 11.1° (range 10-74°) after surgery. The mean increase in the length of the main thoracic curve was 1.5 ± 4.6 mm (range -8 to 13 mm), and the mean increase in T1-L5 length was 16.6 ± 7.7 mm (range -3 to 51 mm). Significant correlation between the correction of the Cobb angle and increase in T1-L5 length was observed, with a correlation coefficient of 0.44. In the PSF group, the mean preoperative Cobb angle of the main thoracic curve was 58.8 ± 11.6° (range 36-107°) and it was corrected to 17.1 ± 7.6° (range 10-49°), with a mean correction of 41.7 ± 10.2° (range 21-73°) after surgery. The mean increase in the length of the main thoracic curve was 14.0 ± 5.2 mm (range 0-42 mm), and the mean increase in T1-L5 length was 32.4 ± 10.8 mm (10-61 mm). Correlation between the correction of the Cobb angle and increase in T1-L5 length was high, with a correlation coefficient of 0.64. The increase in T1-L5 length could be calculated by the following formula based on linear regression analysis: increase in T1-L5 length (mm) = correction of the Cobb angle (8) 9 0.77. Conclusion Spinal longitudinal length was significantly increased after surgery in both the ASF and PSF groups. Correction of the Cobb angle and increase in T1-L5 length were highly correlated with each other, especially in the PSF group.
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