Anterior cruciate ligament (ACL) injury rates are rising, and there is little consensus about what puts someone at risk for an ACL injury. Finite element models provide an effective platform for systemically determining the effect of possible injury risk factors on ACL strain concentrations. However, the accuracy of a finite element model relies on the accuracy of the material models used in its construction. Standard material characterization methods require an assumption of both deformation and material homogeneity, but our recent work has demonstrated that structural features like the shape of the ligament–bone attachment (enthesis) and collagen fiber splay (material direction heterogeneity) create unavoidable deformation heterogeneity. Hence, in this study, full-volume, full-field, finite deformation methods were used to build material models for the ovine ACL bundles and patellar tendon. Specifically, displacement-encoded magnetic resonance imaging (MRI) was used to measure five full-volume deformation fields of each ligament ($n=5$ specimens of each) under tension, and the virtual fields method (VFM) was used to determine material model parameters with these data. This method accounts for strain heterogeneity, principal material direction heterogeneity (fiber splay), and enthesis shape. While most constitutive parameters were consistent among all specimen groups, parameters describing the degree of anisotropy, or collagen fiber alignment, showed statistically significant differences between groups. This work demonstrates that (when strain heterogeneity and structural properties are accounted for) ligament material properties are deterministic and ligament material microstructure is detectable with mesoscale measures of mechanical function.

前交叉韧带 (ACL) 的损伤率正在上升，并且对于什么使某人面临 ACL 损伤的风险几乎没有共识。有限元模型为系统地确定可能的损伤风险因素对 ACL 应变浓度的影响提供了一个有效的平台。但是，有限元模型的准确性取决于其构造中使用的材料模型的准确性。标准的材料表征方法需要对变形和材料均质性进行假设，但我们最近的工作表明，韧带 - 骨附着（附着点）和胶原纤维张开（材料方向异质性）的形状等结构特征会产生不可避免的变形异质性。因此，在本研究中，全容积、全场、有限变形方法用于为绵羊 ACL 束和髌腱建立材料模型。具体而言，位移编码磁共振成像 (MRI) 用于测量每个韧带的五个全体积变形场。$n=5$每个样品）在张力下，并使用虚拟场法（VFM）用这些数据确定材料模型参数。该方法考虑了应变异质性、主要材料方向异质性（纤维展开）和附着点形状。虽然所有样本组的大多数本构参数都是一致的，但描述各向异性程度或胶原纤维排列的参数在组间显示出统计学上的显着差异。这项工作表明（当考虑应变异质性和结构特性时）韧带材料特性是确定性的，韧带材料微观结构可以通过机械功能的中尺度测量来检测。