Ghezelbash F, Eskandari A H, Shirazi-Adl A, Arjmand N, El-Ouaaid Z, Plamondon A
Division of Applied Mechanics, Department of Mechanical Engineering, Ecole Polytechnique, Montréal, Canada.
Department of Mechanical Engineering, Sharif University of Technology, Tehran, Iran.
J Biomech. 2018 Mar 21;70:149-156. doi: 10.1016/j.jbiomech.2017.07.014. Epub 2017 Jul 25.
Musculoskeletal models represent spinal motion segments by spherical joints/beams with linear/nonlinear properties placed at various locations. We investigated the fidelity of these simplified models (i.e., spherical joints with/without rotational springs and beams considering nonlinear/linear properties) in predicting kinematics of the ligamentous spine in comparison with a detailed finite element (FE) model while considering various anterior-posterior joint placements. Using the simplified models with different joint offsets in a subject-specific musculoskeletal model, we computed local spinal forces during forward flexion and compared results with intradiscal pressure measurements. In comparison to the detailed FE model, linearized beam and spherical joint models failed to reproduce kinematics whereas the nonlinear beam model with joint offsets at -2 to +4mm range (+: posterior) showed satisfactory performance. In the musculoskeletal models without a hand-load, removing rotational springs, linearizing passive properties and offsetting the joints posteriorly (by 4mm) increased compression (∼32%, 17% and 11%) and shear (∼63%, 26% and 15%) forces. Posterior shift in beam and spherical joints increased extensor muscle active forces but dropped their passive force components resulting in delayed flexion relaxation and lower antagonistic activity in abdominal muscles. Overall and in sagittally symmetric tasks, shear deformable beams with nonlinear properties performed best followed by the spherical joints with nonlinear rotational springs. Using linear rotational springs or beams is valid only in small flexion angles (<30°) and under small external loads. Joints should be placed at the mid-disc height within -2 to +4mm anterior-posterior range of the disc geometric center and passive properties (joint stiffnesses) should not be overlooked.
肌肉骨骼模型通过放置在不同位置的具有线性/非线性特性的球形关节/梁来表示脊柱运动节段。我们研究了这些简化模型（即带有/不带有旋转弹簧的球形关节以及考虑非线性/线性特性的梁）在预测韧带脊柱运动学方面的逼真度，同时考虑了各种前后关节位置，并与详细的有限元（FE）模型进行了比较。在特定个体的肌肉骨骼模型中使用具有不同关节偏移的简化模型，我们计算了前屈过程中的局部脊柱力，并将结果与椎间盘内压力测量值进行了比较。与详细的有限元模型相比，线性化梁模型和球形关节模型无法再现运动学，而关节偏移在 -2 至 +4mm 范围（+：后方）的非线性梁模型表现出令人满意的性能。在没有手部负载的肌肉骨骼模型中，去除旋转弹簧、线性化被动特性并将关节向后偏移（4mm）会增加压缩力（约 32%、17% 和 11%）和剪切力（约 63%、26% 和 15%）。梁和球形关节的向后移位增加了伸肌的主动力，但降低了它们的被动力分量，导致屈曲松弛延迟，腹肌的拮抗活动降低。总体而言，在矢状面对称任务中，具有非线性特性的剪切可变形梁表现最佳，其次是带有非线性旋转弹簧的球形关节。仅在小屈曲角度（<30°）和小外部负载下使用线性旋转弹簧或梁才是有效的。关节应放置在椎间盘几何中心前后 -2 至 +4mm 范围内的椎间盘中间高度处，并且不应忽视被动特性（关节刚度）。
