Subchondral bone injury due to high magnitude and repetition of compressive loading is common in humans and athletic animals such as Thoroughbred racehorses. Repeated loading of the joint surface may alter the subchondral bone microstructure and initiate microdamage in the bone adjacent to the articular cartilage. Understanding the relationship between microdamage, microstructure and mechanical properties of the subchondral bone adjacent to the articular cartilage is, therefore, essential in understanding the mechanism of subchondral bone injury. In this study, we used high-resolution µCT scanning, a digital image-based strain measurement technique, and mechanical testing to evaluate the three-dimensional pre-existing microcracks, bone volume fraction (BVF) and bone mineral density (BMD), and mechanical properties (stiffness and hysteresis) of subchondral bone (n = 10) from the distopalmar aspect of the third metacarpal (MC3) condyles of Thoroughbred racehorses under high-rate compression. We specifically compared the properties of two regions of interest in the subchondral bone: the 2 mm superficial subchondral bone (SSB) and its underlying 2 mm deep subchondral bone (DSB). The DSB region was 3.0 ± 1.2 times stiffer than its overlying SSB, yet it dissipated much less energy compared to the SSB. There was no correlation between structural properties (BVF and BMD) and mechanical properties (stiffness and energy loss), except for BMD and energy loss in SSB. The lower stiffness of the most superficial subchondral bone in the distal metacarpal condyles may protect the overlying cartilage and the underlying subchondral bone from damage under the high-rate compression experienced during galloping. However, repeated high-rate loading over time has the potential to inhibit bone turnover and induce bone fatigue, consistent with the high prevalence of subchondral bone injury and fractures in athletic humans and racehorses.

在人类和运动动物（如纯种赛马）中，高强度和反复施加压缩载荷会导致软骨下骨损伤。关节表面的反复加载可能会改变软骨下骨的微观结构，并在与关节软骨相邻的骨骼中引发微损伤。因此，了解软骨下软骨的微损伤，微观结构和力学性能之间的关系对于理解软骨下骨损伤的机制至关重要。在这项研究中，我们使用了高分辨率的µCT扫描，一种基于数字图像的应变测量技术以及机械测试来评估三维已存在的微裂纹，骨体积分数（BVF）和骨矿物质密度（BMD），高速压迫的纯种赛马的第三个掌骨（MC3）top的掌顶区的软骨下骨（n = 10）的力学特性（刚度和滞后性）。我们专门比较了软骨下骨中两个感兴趣区域的特性：2 mm浅表软骨下骨（SSB）及其下方的2 mm深软骨下骨（DSB）。DSB区域的硬度是其上覆SSB的3.0±1.2倍，但与SSB相比，其耗散的能量要少得多。除了SSB中的BMD和能量损失外，结构性能（BVF和BMD）与机械性能（刚度和能量损失）之间没有相关性。掌骨远端con中最浅的软骨下骨的较低刚度可以保护上覆的软骨和下面的软骨下骨免受舞动过程中受到的高压力的损害。但是，随着时间的推移反复施加高速率负荷有可能抑制骨骼更新并引起骨骼疲劳，这与软骨下骨损伤和运动型人和赛马骨折的高发率相一致。