Risk Factor Analysis of Mechanical Complications in Surgical Treatment of Thoracolumbar Deformity with Osteoporotic Vertebral Fracture

<b>Objective:</b> Adult spinal deformity (ASD) with osteoporotic vertebral fractures (OVF) often requires vertebral body resection and replacement. However, postoperative mechanical complications (MC) have been unsolved issues. This study retrospectively investigated the risk of MC following anterior-posterior spinal fusion (APF) with vertebral body resection and replacement for OVF with ASD. <b>Methods:</b> Among 91 cases undergoing APF with vertebral body resection and replacement, 43 cases met the deformity criteria. The mean age was 74.2 years, and the mean number of fused segments was 5.7. Pre and postoperative spinal alignments were measured, and the risk of MC occurrence, including PJK, DJK, and cage sinking, was determined through multivariate analysis. The AUC and cutoff values were calculated through ROC analysis. <b>Results:</b> The incidence of MC, PJK, and DJK were 28%, 12%, and 14%, respectively. Multivariate analysis for MC revealed postoperative PI-LL and operative time (cutoff: 40.5 degrees, 238 min) as significant risk factors, while postoperative PI-LL was a significant risk factor for PJK (cutoff: 42.4 degrees). Evaluation considering only thoracolumbar level showed postoperative local kyphosis as a significant MC risk factor (cutoff: 11 degrees). There was a positive correlation between operative time and preoperative local kyphosis, with a cutoff value of 238 min being equivalent to 21 degrees. <b>Conclusion:</b> The postoperative mismatch over 40 degrees and preoperative local kyphosis over 21 degrees were considered as a high risk for MCs. The postoperative kyphosis of 11 degrees was the risk factor of MC in the thoracolumbar level. The meticulous preoperative assessment, including local and global alignment, and local flexibility as well as detailed surgical planning of fixation range and the requirement of osteotomy, are crucial.