Rod fracture (RF) is a complication in adult spinal deformity (ASD) surgery, with a reported incidence rate of 6.8–54% [[1], [2], [3], [4]]. Risk factors associated with RF have been reported in multiple clinical studies and include age, high body mass index, greater preoperative sagittal malalignment, greater sagittal alignment correction, pelvic incidence (PI)–lumbar lordosis (LL) mismatch, fusion to pelvis, 3-column osteotomy, and the use of domino connectors [[3], [4], [5], [6], [7], [8], [9]]. Although additional rods and interbody fusion at L5/S1 have been used as a countermeasure to this complication, RF still occur and continuous studies are being conducted.

Three external forces are involved in RF: bending, correction, and body motion. Previous studies, which were conducted according to international established standards, such as the American Society for Testing Materials (ASTM) F2193 and ASTM F1717, aimed to predict the reliability of the posterior spinal construct components [10,11]. Most finite element analyses (FEA) are concerned with external forces due to body motion [12]. Body motion is validated by applying a follower load to the intact model to simulate the behavior. However, there are no reports examining the effects of intraoperative corrections on the rods.

The purpose of this study was to investigate the effect of ASD correction surgery on rods by using FEA based on the rod shape changes before and after spinal corrective fusion.