McKay Orthopaedic Research Laboratory, University of Pennsylvania, Philadelphia, Pennsylvania.
Department of Orthopaedic Surgery, Wake Forest School of Medicine, Winston-Salem, North Carolina.
J Orthop Res. 2020 Jan;38(1):36-42. doi: 10.1002/jor.24407. Epub 2019 Jul 23.
In tendon, type-I collagen assembles together into fibrils, fibers, and fascicles that exhibit a wavy or crimped pattern that uncrimps with applied tensile loading. This structural property has been observed across multiple tendons throughout aging and may play an important role in tendon viscoelasticity, response to fatigue loading, healing, and development. Previous work has shown that crimp is permanently altered with the application of fatigue loading. This opens the possibility of evaluating tendon crimp as a clinical surrogate of tissue damage. The purpose of this study was to determine how fatigue loading in tendon affects crimp and mechanical properties throughout aging and between tendon types. Mouse patellar tendons (PT) and flexor digitorum longus (FDL) tendons were fatigue loaded while an integrated plane polariscope simultaneously assessed crimp properties at P150 and P570 days of age to model mature and aged tendon phenotypes (N = 10-11/group). Tendon type, fatigue loading, and aging were found to differentially affect tendon mechanical and crimp properties. FDL tendons had higher modulus and hysteresis, whereas the PT showed more laxity and toe region strain throughout aging. Crimp frequency was consistently higher in FDL compared with PT throughout fatigue loading, whereas the crimp amplitude was cycle dependent. This differential response based on tendon type and age further suggests that the FDL and the PT respond differently to fatigue loading and that this response is age-dependent. Together, our findings suggest that the mechanical and structural effects of fatigue loading are specific to tendon type and age in mice. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:36-42, 2020.
在肌腱中，I 型胶原组装成原纤维、纤维和束，这些结构呈现出波浪状或卷曲状，在施加拉伸载荷时会展开。这种结构特性在多个肌腱中都有观察到，可能在肌腱粘弹性、对疲劳加载的响应、愈合和发育中发挥重要作用。以前的工作表明，随着疲劳加载的应用，卷曲会永久改变。这为评估肌腱卷曲作为组织损伤的临床替代物提供了可能性。本研究旨在确定肌腱疲劳加载如何影响整个衰老过程中和不同肌腱类型之间的卷曲和机械性能。在 150 天和 570 天龄（模拟成熟和衰老肌腱表型）时，使用集成平面偏光镜同时评估肌腱的卷曲特性，对小鼠髌腱（PT）和指深屈肌腱（FDL）进行疲劳加载（每组 N=10-11）。结果发现，肌腱类型、疲劳加载和衰老对肌腱的机械和卷曲性能有不同的影响。FDL 肌腱的模量和滞后较高，而 PT 肌腱在整个衰老过程中表现出较大的松弛和脚趾区域应变。在整个疲劳加载过程中，FDL 的卷曲频率始终高于 PT，而卷曲幅度则与循环有关。基于肌腱类型和年龄的这种差异反应进一步表明，FDL 和 PT 对疲劳加载的反应不同，这种反应是年龄依赖性的。总之，我们的研究结果表明，疲劳加载对小鼠肌腱的机械和结构影响具有特异性，取决于肌腱类型和年龄。
