Finite element analysis of C5-6 segment biomechanics under axial loads in different postures

English Keywords:Cervical spine  Posture  Axial compressive force  Biomechanics  Finite element analysis

English Abstract:

  【Abstract】 Objectives: To investigate the biomechanical characteristics of the C5-6 segment under axial compressive load in different postures. Methods: A three-dimensional finite element model of the C5-6 segment was constructed based on the CT data of a 28-year-old healthy male volunteer, and the validity of the model was verified by comparing the range of motion(ROM) of the model with previous studies. Seven postures, including flexion, extension, left lateral bending, right lateral bending, left rotation, right rotation and neutral position, were simulated, and an axial compressive load of 7000N was applied on the superior endplate. The distributions of equivalent stress/equivalent strain, minimum principal stress/minimum principal strain, shear stress/shear strain in the C5, C6 vertebral bodies and intervertebral discs under different postures were analyzed, and the Kruskal-Wallis test was used to evaluate the differences between different postures. Results: Under axial load, the maximum value of the peak equivalent stress of the C5 vertebral body was 370.09MPa, located at the junction of the left pedicle and the vertebral body in the extension posture, and the minimum value was 289.30MPa, located at the anterior part of the right uncinate process of the upper vertebral body in the neutral posture. The maximum value of the peak equivalent strain was 0.132, located at the anterior part of the left uncinate process in the left lateral bending posture, and the minimum value was 0.094, located at the same region in the left rotation posture. The equivalent stress of the C5 vertebral body was mainly concentrated in the vertebral body, pedicle, around the transverse foramen and endplate, while the equivalent strain was mainly concentrated in the endplate and uncinate process. For the C6 vertebral body, both the maximum value of the peak equivalent stress(305.94MPa) and the maximum value of the peak equivalent strain(0.159) were located at the right posterolateral edge of the inferior endplate of the vertebral body in the extension posture; the minimum value of the peak equivalent stress(167.14MPa) and the minimum value of the peak equivalent strain(0.094) both appeared at the same region in the flexion posture. The equivalent stress and equivalent strain of the C6 vertebral body were mainly concentrated in the vertebral body, around the transverse foramen and endplate. For the intervertebral disc, both the maximum value of the peak equivalent stress(53.47MPa) and the maximum value of the peak equivalent strain(16.346) were located at the middle of the anterolateral edge in the flexion posture; the minimum values of the peak equivalent stress and peak equivalent strain were both located at the right lateral edge in the extension posture, and the equivalent stress and equivalent strain of the intervertebral disc were mainly concentrated at the lateral edge. The maximum value of the peak minimum principal stress of the C5 vertebral body was 388.81MPa, located at the left pedicle in the extension posture, and the minimum value was 309.76MPa, located at the anterolateral part of the right endplate in the neutral posture. The maximum value of the peak minimum principal strain was 0.104, located at the anteromedial part of the left pedicle in the left lateral bending posture, and the minimum value was 0.075, located at the same region in the neutral posture. The minimum principal stress of the C5 vertebral body was mainly concentrated in the endplate, pedicle and vertebral body, and the minimum principal strain was mainly concentrated in the superior endplate, uncinate process and pedicle. For the C6 vertebral body, the maximum values of the peak minimum principal stress and peak minimum principal strain were 1281.90MPa and 0.184, respectively, both located at the right posterolateral edge of the inferior endplate of the vertebral body in the right lateral bending posture; the minimum values of the peak values were 808.12MPa and 0.116, respectively, both located at the same region in the flexion posture. The minimum principal stress and minimum principal strain of the C6 vertebral body were mainly concentrated in the endplate, pedicle and vertebral body. For the intervertebral disc, the maximum values of the peak minimum principal stress and peak minimum principal strain were 83.91MPa and 16.895, respectively, both located at the middle of the anterolateral edge of the intervertebral disc in the flexion posture; the minimum values of the peak values were 65.06MPa and 12.791, respectively, both located at the right lateral edge of the intervertebral disc in the extension posture. The minimum principal stress and minimum principal strain of the intervertebral disc were both concentrated at the lateral edge. The maximum value of the peak shear stress of the C5 vertebral body was 206.07MPa, located at the left pedicle in the extension posture, and the minimum value was 155.76MPa, located at the anterior part of the upper right vertebral body in the flexion posture. The maximum value of the peak shear strain was 0.213, located at the anterior part of the left uncinate process in the left lateral bending posture, and the minimum value was 0.150, located at the same region in the left rotation posture. The shear stress and shear strain of the C5 vertebral body were concentrated in the superior endplate, uncinate process and pedicle. For the C6 vertebral body, both the maximum value of the peak shear stress(664.36MPa) and the maximum value of the peak shear strain(0.230) were located at the right posterolateral edge of the inferior endplate of the vertebral body in the right lateral bending posture; the minimum value of the peak shear stress(422.40MPa) and the minimum value of the peak shear strain(0.136) both appeared at the same region in the flexion posture. The shear stress and shear strain of the C6 vertebral body were mainly concentrated in the inferior endplate and pedicle. The maximum value of the peak shear stress of the intervertebral disc was 30.30MPa, located at the left middle part of the anterolateral edge of the intervertebral disc in the flexion posture, and the minimum value was 22.60MPa, located at the right lateral edge of the intervertebral disc in the extension posture. The maximum value of the peak shear strain was 24.954, located at the middle of the anterolateral edge of the intervertebral disc in the flexion posture, and the minimum value was 18.608, located at the right lateral edge of the intervertebral disc in the extension posture. The shear stress and shear strain of the intervertebral disc were concentrated at the lateral edge. Conclusions: Under axial compressive load, there are significant differences in the stress and strain distributions of the vertebral bodies and intervertebral disc of the C5-6 segment in different postures. The vertebral body stress is the largest and concentrated in the posterior region in the extension posture; the anterolateral strain of the intervertebral disc is concentrated in the flexion posture; and the ipsilateral vertebral body stress is increased in the lateral bending posture.