Three-dimensional finite element analysis of stress distribution of lower cervical intervertebral disc and articular process cartilage in different O-EA angles after occipitocervical internal fixation

English Keywords:Complete cervical model with external auditory canal  O-EA angle  Finite element  Biomechanics

English Abstract:

  【Abstract】 Objectives: A three-dimensional finite element model of the whole cervical spine with external auditory canal of occiput and external acoustic meatus to axis angle(O-EA angle) of 80°, 95°, and 110° and equipped with occipitocervical internal fixation system was constructed to study the stress distribution of the lower cervical intervertebral disc and articular process cartilage. Methods: Based on the CT source data of the total cervical spine with external auditory canal of a 29-year-old healthy man, and computed by Mimics 19.0, Geomagic Studio 2015, and Solid Works 2018 software, to establish a three-dimensional finite element model of the whole cervical spine with external auditory canal of O-EA angle of 80°, 95°, and 110° and equipped with occipitocervical internal fixation system. A net torque of 1.5N·m was applied along the skull base surface above the odontoid process, and 75N was applied to simulate skull weight. The stress peaks of C5/6 and C6/7 intervertebral discs and the articular cartilage of C6 and C7 under the conditions of forward flexion, posterior flexion, left flexion and left rotation were measured and compared. Results: The finite element analysis model with external auditory canal was successfully established to simulate occipital and cervical fixation at different O-EA angles(80°, 95°, and 110°). The Von Mise stress peak values of C5/6, C6/7 intervertebral discs, and C6, C7 superior articular process cartilages under flexion, extension and left rotation conditions were smaller than those of the models with O-EA angle of 80° and 110°. Under the left flexion condition, the stress peak of the C5/6 intervertebral disc and the upper articular process of C6 and 7 at O-EA angle of 95° was greater than that at O-EA angle of 80° and 110°, while the stress peak of the C6/7 intervertebral disc at O-EA angle of 95° was greater than that at O-EA angle 110° and less than O-EA angle 80°. Conclusions: The results of three-dimensional finite element analysis indicate that the O-EA angle should be paid attention during occipitocervical internal fixation. The improper O-EA angle may cause the increase of Von-Mise stress peak value of C5/6, C6/7 intervertebral disc and C6, C7 superior articular process cartilage, and then accelerate the degeneration of the lower cervical spine.