Preoperative Low Lumbar Hounsfield Units and Global Alignment Predict Postoperative Mechanical Complications After Adult Spinal Deformity Surgery: A Multicenter Retrospective Study

<b>Objectives:</b> This study investigated the potential of Hounsfield unit (HU) values obtained from computed tomography (CT) scans as predictors of mechanical complications (MCs) in patients undergoing long-segment spinal fusion involving the pelvis. Additionally, it identified a threshold HU value associated with an increased risk of MCs. <b>Methods:</b> We conducted a retrospective, multicenter review of patients who underwent long-segment spinal fusion involving the pelvis, with a minimum follow-up period of two years. Patients were categorized based on the presence or absence of postoperative MCs. Both preoperative and postoperative radiographic parameters were analyzed, and HU values were quantified from CT images. Logistic regression modeling was used to identify independent risk factors for MCs. <b>Results:</b> Among 129 patients, 33 (25.6%) developed MCs, including proximal and distal junctional failures, rod fractures, and cases necessitating re-operation. The HU values were significantly lower in the MC group, whereas conventional bone mineral density (BMD) measurements showed no significant difference. Global alignment parameters, such as the sagittal vertical axis (SVA) and global tilt (GT), were consistently higher in patients with MCs. Receiver operating characteristic analysis identified 131 HU as the optimal cut-off, yielding a sensitivity of 56.4% and a specificity of 69.7%. Multivariate analysis confirmed that lower HU values were independently associated with the occurrence of MCs. <b>Conclusions:</b> Lower HU values and larger radiological global alignment parameters are significant predictors of MCs in patients undergoing surgery for adult spinal deformity. These findings underscore the importance of CT-based quantitative assessments in preoperative planning.