Pedicle Hounsfield Unit Threshold for Predicting Screw Malposition İn Idiopathic and Degenerative Scoliosis Surgery

Study Design Retrospective comparative study. Objective To investigate the relationship between pedicle Hounsfield Unit (HU) values and transpedicular screw malposition in scoliosis surgery and to determine a predictive HU threshold for malposition risk. Methods Patients who underwent free transpedicular screw fixation for idiopathic or degenerative scoliosis between 2011 and 2024 and had both preoperative and early postoperative spinal computed tomography (CT) scans available were retrospectively reviewed. Screw malposition was identified on postoperative CT, and pedicle HU values and the widths of malpositioned screws were measured on the corresponding preoperative CT images and compared with contralateral and control pedicles. Receiver operating characteristic (ROC) analysis was used to determine a predictive HU threshold for screw malposition. Results The study included 121 patients. Mean HU values were significantly higher in malpositioned pedicles compared to controls in both the idiopathic (692 vs 299.5; P < 0.001) and degenerative scoliosis (343.5 vs 250; P < 0.001) groups. ROC analysis determined the HU cut-off value to be 479 and above to predict screw malposition (AUC = 0.796; 95% CI: 0.717-0.876; sensitivity 73.6%, specificity 79.6%). The location of screw malposition according to the convex and concave sides, and the location above and below the apex did not show any significant differences. Conclusion Higher pedicle HU values are significantly associated with screw malposition in scoliosis surgery. A HU threshold of 479 may help identify pedicles at increased risk of malposition during free screw placement in both idiopathic and degenerative scoliosis. Preoperative pedicle HU assessment may contribute to surgical planning and risk reduction strategies.