Loss of apical vertebral derotation in adolescent idiopathic scoliosis: 2-year follow-up using multi-planar reconstruction computed tomography

Abstract

The objective of this study was to evaluate 2years post-surgical loss of three-dimensional correction in adolescent idiopathic scoliosis (AIS) patients using multi-planar reconstruction computed tomography (CT). Twenty-seven AIS patients treated by segmental pedicle screw (PS) constructs were included in this study. Correction in the axial plane was evaluated using the "relative apical vertebral rotation angle" (rAVR), defined as the difference between the axial rotation angles of the upper instrumented vertebra and the apical vertebra on reconstructed axial CT images. The Cobb angle of the main curve and apical vertebral translation was measured to evaluate the coronal correction. Thoracic kyphosis was also measured for the evaluation of sagittal profile. Measurements were performed before surgery, and 1week and 2years after surgery. The relationships between the correction losses and skeletal maturity, and variety of spinal constructs were also evaluated. The mean preoperative Cobb angle of the major curve was 59.1°±11.2° before and 13.0°±7.2° immediately after surgery. Two years later, the mean Cobb angle had increased significantly, to 15.5°±7.8°, with a mean correction loss of 2.5°±1.5° (p<0.001). The mean preoperative rAVR of 28.5°±8.4° was corrected to 15.8°±7.8° after surgery. It had increased significantly to 18.5±8.4 by 2years after surgery, with a mean correction loss of 2.7°±1.0° (p<0.001). The mean correction losses for both the Cobb angle and rAVR were significantly greater in the skeletally immature patients. The significant correlations were recognized between the correction losses and the proportion of multi-axial screws, and the materials of constructs. Statistically significant loss of correction in the Cobb angle and apical vertebral axial rotation angle (AVR) were recognized 2years after surgery using PS constructs. The correction losses, especially AVR, were more evident in the skeletally immature patients, and in patients treated with more multi-axial screws and with titanium constructs rather than with stainless constructs.