Is the morphology of the apical pedicles influenced by apical rotation or the coronal curve magnitude in adolescent idiopathic scoliosis?: a radiographic assessment.

INTRODUCTION:Asymmetry in pedicle anatomy is most distinctly noted around the apex of the curve. The correlation of pedicle dysmorphia with apical vertebral rotation (AVR) and coronal Cobb angle (CCA) has not been studied. OBJECTIVE:To establish whether pedicle dysmorphism is linked to curve magnitude CCA and the AVR in adolescent idiopathic scoliosis (AIS). METHODOLOGY:Preoperative plain whole spine standing radiographs and non-contrast computed tomography (CT) scans of 25 AIS patients that were operated at a single centre from 2013 to 2019 were retrospectively reviewed by 3 independent co-investigators. CCA was noted on the standing radiograph, whereas the AVR was measured on the axial cuts of CT scan. Pedicle morphometric measurements were performed for apical and periapical pedicles. These included apical vertebra (when present), 2 vertebrae above (U1 and U2) and below (B1 and B2) the apex vertebra/disc. The pedicle morphometric measurements were performed on CT scans. We assessed the transverse pedicle diameter, transverse cancellous channel diameter, sagittal pedicle diameter, pedicle length and pedicle axis length. Correlation tests between various pedicle morphometric measurements, AVR and the curve magnitude (Cobb angle) was performed by the Pearson correlation test. RESULTS:The apex of the major curve was in the thoracic spine in 20 patients, thoracolumbar in three patients and in the lumbar spine in two patients. The mean Cobb angle was 61.5 ± 9.3° and the mean AVR was 28.4 ± 17.8°. A positive correlation was noted with the AVR for U1 concave pedicle length (r = 0.45, p = 0.03), pedicle axis length of the U2 concave pedicle (r = 0.6, p = 0.04), transverse pedicle diameter of the convex apical vertebrae (r = 0.82, p = 0.00009) and the convex apical transverse pedicle diameter (r = 0.80, p = 0.002). A negative correlation with the AVR was noted for U2 convex pedicle length (r = - 0.51, p = 0009), transverse cancellous channel diameter of the U2 concave pedicle (r = - 0.42, p = 0.04) and apical concave pedicle (r = - 0.78, p = 0.002) and the sagittal pedicle diameter for the convex pedicle of U2 (r = - 0.45, p = 0.03) and apex(r = - 0.59, p = 0.04). The Cobb angle did not show a significant correlation with any of the pedicle measurements at any of the levels on the convex and the concave sides. CONCLUSION:Pedicle asymmetry and dysmorphism demonstrate a morphometric association with the apical vertebral rotation than the curve magnitude. The pedicle length and the pedicle axis length increase on the concave apical and periapical region with increase in AVR. The transverse cancellous channel diameter significantly decreases on the concave apical region with the increase in AVR. The sagittal pedicle diameter decreases on the convex side with the increase in AVR.