Finite Element Analysis of Biomechanical Behavior of Whole Thoraco-lumbar Spine with Ligamentous Effect

Chin-Chun Lan ； Ching-Sung Kuo ； Cheng-Hsiung Chen ； Hsuan-Teh Hu

《The Changhua Journal of Medicine》 11卷1期 (2013/09) Pp. 26-41

並列摘要

Objective. To evaluate the biomechanical behavior of whole thoraco-lumbar spine by performing numerical analyses with finite element method on a proposed model for thoraco-lumbar spine.Background. Many studies on functional spinal units (FSU) in lumbar, thoracic or cervical spine have been done. However, the biomechanical behavior of whole spine was rarely explored. Previous models of whole spine were too simplified to describe the biomechanical behavior of spine in a realistic way. To investigate this issue, the authors simulated various types of motion by finite element method to determine the mechanical response of whole spine, such as relative rotational angles, von-Mises stress distribution, and associated vibrational modes.Methods. A three-dimensional finite element model of the whole thoracolumbar spine was developed and validated. Four types of spinal motion were simulated, including flexion, extension, lateral bending, and axial rotation. Axial loads of 14N and 140N were exerted on the top endplate of the T1 vertebra to represent light and heavy preloads respectively. A total moment of 14.5Nm was applied to activate the various spinal motions. Sacroiliac joint was set fixed in the numerical simulation. This study adopted linear and isotropic material properties for most spinal components, such as the cancellous bone, cortical shell, posterior bone, endplate, annulus ground substance, and nucleus pulposus. Annulus fibrosus was modeled as two layers of fiber laminate. Each laminate consisted of three plies, which were stacked together with an angle of +30° or -30°. As to the ligaments, both linear and nonlinear behaviors were considered to make the model more realistic.Results. The numerical results demonstrated that, during extension motion, the maximum rotational angle (3.92°) occurred at L2-L3 level and the maximum von-Mises stress (52.64 MPa) developed at the superior endplate of L3. During flexion motion, the maximum rotational angle was 3.11° at L2-L3 level and a maximum von-Mises stress of 39.8 MPa was imposed on the superior endplates of L3. Lateral bending resulted in a maximum rotational angle of 2.77° at L2-L3 level and a maximum von-Mises stress of 61.03 MPa at the superior endplate of L3. Axial rotation produced a maximum rotational angle of, 4.17° at L2-L3 level and a maximum von-Mises stress of 53.2 MPa on the cortical bone of vertebra L2. The effects of linear-type ligaments and nonlinear-type ligaments were compared. The relative deformation of FSU’s had the same trend in both linear and nonlinear ligaments. The calculated results indicated that the spine had more flexibility when the nonlinearity of ligaments was taken into consideration. The first ten vibration modes and the corresponding natural frequencies with participation factors were obtained.; The first ten resonant frequencies of our model ranged from 0.008 to 0.2 Hz. Our calculated results were relatively lower than one FSU (2 segments) which was modeled in the previous studies. This observation is consistent with the fact that resonant frequencies decrease with increase in the number of motion segments, as pointed out by the literature..

並列關鍵字

Finite element method ； Thoraco-lumbar spine ； Vibration mode ； Natural frequency ； Nonlinear behavior