Abstract：
The Achilles tendon enthesis (ATE) anchors the Achilles tendon into the calcaneus through fibrocartilaginous tissue. The latter is enriched in type II collagen and proteoglycans (PGs), both of which give the enthesis its capacity to withstand compressive stress. Because unloading and reloading induce remodeling of the ATE fibrocartilage (Camy et al., 2022), chronic changes in the mechanical load could modify the mechanical response under compressive stress. Therefore, we investigated the ATE fatigue behavior in mice, under cyclic compressive loading, after 14 days of hindlimb suspension and 6 days of reloading. In addition, we performed a qualitative histological study of PGs in ATE fibrocartilage. The mechanical behavior of ATE was impaired in unloaded mice. A significant loss of 27 % in Δd (difference between the maximum and minimum displacements) was observed at the end of the test. In addition, the hysteresis area decreased by approximately 27 % and the stiffness increased by over 45 %. The increased stiffness and loss of viscosity were thrice and almost twice those of the control, respectively. In the reloaded entheses, where the loss of Δd was not significant, we found a significant 28 % decrease in the hysteresis area and a 26 % increase in stiffness, both of which were higher regarding the control condition. These load-dependent changes in the mechanical response seem partly related to changes in PGs in the uncalficied part of the ATE. These findings highlight the importance of managing compressive loading on ATE when performing prophylactic and rehabilitation exercises.
摘要：
跟腱（ATE）通过纤维软骨组织将跟腱锚固到跟骨中。后者富含II型胶原蛋白和蛋白聚糖（PG），这两者都赋予了它承受压应力的能力。因为卸载和重新加载会诱导ATE纤维软骨的重塑(Camy等人。,2022),机械载荷的长期变化可能会改变压应力下的机械响应。因此,我们调查了小鼠的ATE疲劳行为，在循环压缩载荷下，后肢悬吊14天和重新加载6天后。此外,我们对ATE纤维软骨中的PGs进行了定性组织学研究。在空载小鼠中，ATE的机械行为受损。在测试结束时观察到27%的Δd(最大和最小位移之间的差)的显著损失。此外,滞后面积减少了约27%，刚度增加了45%以上。增加的刚度和粘度损失是对照组的三倍，几乎是对照组的两倍，分别。在重新加载的论文中，其中Δd的损失不显著，我们发现滞后面积显著减少28%，刚度增加26%，就控制条件而言，两者都较高。机械响应中的这些与负载相关的变化似乎部分地与ATE的未处理部分中PG的变化有关。这些发现强调了在进行预防和康复锻炼时管理ATE上的压缩负荷的重要性。
