PURPOSE: The purpose of the study is to assess the MRI predictability of pedicle dimensions in AIS patients with curve magnitude more than 50° and to determine the influence of curve magnitude and vertebral rotation on MRI predictability. METHODS: The study included a comparative analysis of preoperative MRI (pMRI), and intraoperative CT (iCT) scan images of surgically corrected AIS patients with a curve magnitude of more than 50°. Bilateral T2-L4 pedicle levels were evaluated to measure the chord length and isthmic diameter in pMRI and iCT axial cuts. Vertebral rotation was assessed using the Nash and Moe method. Patients were categorised based on structural curve magnitude into group 1 (50°-70°), group 2 (71°-90°), and group 3 (> 90°). RESULTS: A total of 1860 pedicles in 62 patients were analysed. Comparison between iCT and pMRI measurements showed excellent reliability (ICC > 0.90) for pedicle diameter at all levels except the apical levels. Comparison based on curve magnitude revealed at the apical levels showed good correlation (ICC = 0.87) in Group 1, moderate correlation (ICC = 0.75) in Group 2 and poor reliability (ICC = 0.37) in Group 3. However, the pedicle length showed excellent reliability (ICC = 0.92) across all three groups. Moreover, MRI reliability for predicting vertebral dimensions decreased as the degree of rotation increased. CONCLUSIONS: Both the curve magnitude and vertebral rotation significantly impact the MRI prediction of the pedicle dimensions, with predictability decreasing as the curve magnitude and vertebral rotation increase.