Stress distribution of pedicle screw fixation for thoracolumbar fractures with finite element analysis / 中国组织工程研究

ABSTRACT

BACKGROUND:Spinal surgery requires a relatively high accuracy. At present, the study of pedicle screw fixation is more focused on the safety and stability, but the premise is the safe and effective screw placement. Selection of the insertion point is the key to success. OBJECTIVE:To analyze stress distribution of different pedicle screw implantation methods for thoracolumbar fractures by using finite element analysis. METHODS:T9-L3 segments of a thoracolumbar burst fractures patient were scanned in the Department of Orthopedics, Zhaoqing City First People’s Hospital in January 2015. 616 CT Dicom images were obtained and introduced into engineering software. Finite element geometric model was established. Posterior approach orthopedic surgery was simulated. Stress distribution after pedicle screw fixation for thoracolumbar fractures was analyzed. RESULTS AND CONCLUSION:(1) The three-dimensional motion range of the fixation with six screws and two rods was small in anteflexion, lateral bending, and axial rotation, followed by five screws and two rods by posterior approach (single right vertebral fixation). The motion range of the fixation with four screws and two rods was biggest, but biomechanical stability was poorest. (2) In different fixation models, upper screw stress was larger in anteflexion than other states in the fixation with four screws and two rods by posterior trans-traumatic-vertebra, four screws and two rods by posterior injured vertebra, six screws and two rods by posterior injured vertebra, five screws and two rods by posterior approach (single right injured vertebra) and six screws and two rods by posterior approach (upper injured vertebra), followed by left axial rotation and right axial rotation. Significant differences in screw stress were found in different motion states (P < 0.05). (3) In different fixation modes, the stress ratio of upper and lower screws was significantly larger in the fixation with four screws and two rods by posterior trans-traumatic-vertebra, four screws and two rods by posterior injured vertebra, six screws and two rods by posterior injured vertebra, five screws and two rods by posterior approach (single right injured vertebra) and six screws and two rods by posterior approach (upper injured vertebra) than other motion states (P < 0.05), followed by right axial rotation and right lateral bending. Significant differences in stress ratio of upper and lower screws were detectable in different motion states (P < 0.05). (4) Results suggested that finite element analysis could better simulate complex spine mechanical system, accurately reflect the stress distribution of spinal pedicle screw model, and provide the basis for making pedicle screw program.