Lewis Katz School of Medicine at Temple University, Department of Anatomy and Cell Biology, Philadelphia, PA 19140, United States.
Lewis Katz School of Medicine at Temple University, Department of Anatomy and Cell Biology, Philadelphia, PA 19140, United States.
Bone. 2018 May;110:267-283. doi: 10.1016/j.bone.2018.02.014. Epub 2018 Feb 22.
We have an operant rat model of upper extremity reaching and grasping in which we examined the impact of performing a high force high repetition (High-ForceHR) versus a low force low repetition (Low-ForceHR) task for 18weeks on the radius and ulna, compared to age-matched controls. High-ForceHR rats performed at 4 reaches/min and 50% of their maximum voluntary pulling force for 2h/day, 3days/week. Low-ForceHR rats performed at 6% maximum voluntary pulling force. High-ForceHR rats showed decreased trabecular bone volume in the distal metaphyseal radius, decreased anabolic indices in this same bone region (e.g., decreased osteoblasts and bone formation rate), and increased catabolic indices (e.g., microcracks, increased osteocyte apoptosis, secreted sclerostin, RANKL, and osteoclast numbers), compared to controls. Distal metaphyseal trabeculae in the ulna of High-ForceHR rats showed a non-significant decrease in bone volume, some catabolic indices (e.g., decreased trabecular numbers) yet also some anabolic indices (e.g., increased osteoblasts and trabecular thickness). In contrast, the mid-diaphyseal region of High-ForceHR rats' radial and ulnar bones showed few to no microarchitecture differences and no changes in apoptosis, sclerostin or RANKL levels, compared to controls. In further contrast, Low-ForceHR rats showed increased trabecular bone volume in the radius in the distal metaphysis and increased cortical bone area its mid-diaphysis. These changes were accompanied by increased anabolic indices, no microcracks or osteocyte apoptosis, and decreased RANKL in each region, compared to controls. Ulnar bones of Low-ForceHR rats also showed increased anabolic indices, although fewer than in the adjacent radius. Thus, prolonged performance of an upper extremity reaching and grasping task is loading-, region-, and bone-dependent, with high force loads at high repetition rates inducing region-specific increases in bone degradative changes that were most prominent in distal radial trabeculae, while low force task loads at high repetition rates induced adaptive bone responses.
我们建立了一个上肢伸及抓握的操作性大鼠模型，在此模型中，我们研究了连续 18 周执行高力高重复（High-ForceHR）和低力低重复（Low-ForceHR）任务对桡骨和尺骨的影响，并与年龄匹配的对照组进行比较。高力高重复组大鼠以 4 次/分钟的速度进行 2 小时/天、3 天/周的操作，达到其最大自主拉力的 50%。低力高重复组大鼠的拉力为最大自主拉力的 6%。与对照组相比，高力高重复组大鼠桡骨远端干骺端的骨小梁体积减少，该骨区域的合成代谢指数（例如，成骨细胞和骨形成率降低）降低，分解代谢指数（例如，微骨折、骨细胞凋亡增加、分泌的硬化蛋白、RANKL 和破骨细胞数量增加）增加。与对照组相比，高力高重复组大鼠尺骨远端干骺端的骨小梁体积虽略有减少，但也出现了一些分解代谢指数（例如，小梁数量减少）和一些合成代谢指数（例如，成骨细胞和小梁厚度增加）。相比之下，高力高重复组大鼠桡骨和尺骨的中轴骨区域很少或没有微结构差异，骨细胞凋亡、硬化蛋白或 RANKL 水平也没有变化。相比之下，低力高重复组大鼠桡骨远端干骺端的骨小梁体积增加，中轴骨的皮质骨面积增加。这些变化伴随着合成代谢指数的增加、没有微骨折或骨细胞凋亡以及每个区域的 RANKL 减少，与对照组相比。低力高重复组大鼠的尺骨也表现出合成代谢指数的增加，尽管低于相邻的桡骨。因此，上肢伸及抓握任务的持续执行是负载、部位和骨骼依赖性的，高力高重复率的负载会导致特定部位的骨降解变化增加，这些变化在桡骨远端小梁中最为明显，而低力高重复率的负载会引起适应性的骨骼反应。
