Department of Biomedical Engineering, University of Virginia, Charlottesville, VA, USA.
Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand.
J Biomech. 2022 Jan;130:110877. doi: 10.1016/j.jbiomech.2021.110877. Epub 2021 Nov 27.
The soleus is an important plantarflexor muscle with complex fascicle and connective tissue arrangement. In this study we created an image-based finite element model representing the 3D structure of the soleus muscle and its aponeurosis connective tissue, including distinct fascicle architecture of the posterior and anterior compartments. The model was used to simulate passive and active soleus lengthening during ankle motion to predict tissue displacements and fascicle architecture changes. Both the model's initial architecture and changes incurred during passive lengthening were consistent with prior in vivo data from diffusion tensor imaging. Model predictions of active lengthening were consistent with axial plane muscle displacements that we measured in eight subjects' lower legs using cine DENSE (Displacement Encoding with Stimulated Echoes) MRI during eccentric dorsiflexion. Regional strains were variable and nonuniform in the model, but average fascicle strains were similar between the compartments for both passive (anterior: 0.18 ± 0.06, posterior: 0.19 ± 0.05) and active (anterior: 0.12 ± 0.05, posterior: 0.13 ± 0.06) lengthening and were two- to three-times greater than muscle belly strain (0.06). We used additional model simulations to investigate the effects of aponeurosis material properties on muscle deformation, by independently varying the longitudinal or transverse stiffness of the posterior or anterior aponeurosis. Results of model variations elucidate how properties of soleus aponeuroses contribute to fascicle architecture changes. Greater longitudinal stiffness of posterior compared to anterior aponeurosis promoted more uniform spatial distribution of muscle tissue deformation. Reduced transverse stiffness in both aponeuroses resulted in larger differences between passive and active soleus lengthening.
比目鱼肌是一种重要的跖屈肌，具有复杂的肌束和结缔组织排列。在这项研究中，我们创建了一个基于图像的有限元模型，代表比目鱼肌及其腱膜结缔组织的 3D 结构，包括后、前间隔的不同肌束结构。该模型用于模拟踝关节运动过程中的被动和主动比目鱼肌延长，以预测组织位移和肌束结构变化。模型的初始结构和被动延长过程中的变化与之前扩散张量成像的体内数据一致。模型对主动延长的预测与我们在 8 名受试者小腿使用电影 DENSE（位移编码与刺激回波）MRI 在离心背屈期间测量的轴向平面肌肉位移一致。模型中的区域应变是可变的和不均匀的，但在被动延长（前间隔：0.18±0.06，后间隔：0.19±0.05）和主动延长（前间隔：0.12±0.05，后间隔：0.13±0.06）中，两个间隔之间的平均肌束应变相似，并且比肌腹应变（0.06）大两到三倍。我们使用额外的模型模拟来研究腱膜材料特性对肌肉变形的影响，通过独立改变后腱膜或前腱膜的纵向或横向刚度。模型变化的结果阐明了比目鱼肌腱膜的特性如何影响肌束结构的变化。与前腱膜相比，后腱膜的纵向刚度更大，促进了肌肉组织变形的更均匀的空间分布。前后腱膜的横向刚度降低导致被动和主动比目鱼肌延长之间的差异更大。
