Biomechanical Analysis of Adjacent Segments after Correction Surgery for Adult Idiopathic Scoliosis: A Finite Element Analysis

Abstract

Abstract Background The biomechanical aspects of adjacent segment degeneration after adult idiopathic scoliosis correction surgery involving postoperative changes in motion and stress of adjacent segments have yet to be investigated. The objective of this study was to evaluate the biomechanical effects of correction surgery on adjacent segments in adult idiopathic scoliosis by finite element analysis. Methods Based on computed tomography data of the consecutive spine from T1–S1 of a 28-year-old male patient with adult idiopathic scoliosis, a three-dimensional finite element model was established to simulate the biomechanics. Two posterior long-segment fixation and fusion operations were designed: Strategy A, pedicle screws implanted in all segments of both sides, and Strategy B, alternate screws instrumentation on both sides. The range of motion, maximum von Mises stress of intervertebral disc, and von Mises stress of the facet joint at the fixation adjacent segment were calculated and compared with data of the preoperative AdIS model. Results Correction surgery decreased the stress on the adjacent intervertebral disc, increased stress on the adjacent facet joint, and decreased range of motion of the adjacent segments. A greater decrease of maximum von Mises stress was observed on the distal adjacent segment compared with the proximal adjacent segment. The decrease of maximum von Mises stress and increment of maximum von Mises stress on adjacent facet joints in strategy B was greater than that in strategy A. Under the six operation modes, the change of the maximum von Mises stress on the adjacent intervertebral disc and facet joint was significant. The decrease in range of motion in the proximal adjacent segment was greater than that of the distal adjacent segment, and the decrease of range of motion in strategy A was greater than that in strategy B. Conclusions This study clarified the biomechanical characteristics of adjacent segments after adult idiopathic scoliosis correction surgery, and further biomechanical analysis of two different posterior pedicle screw placement schemes by finite element method. Our study provides a theoretical basis for the pathogenesis, prevention, and treatment of adjacent segment degeneration after correction surgery for adult idiopathic scoliosis.