Biomechanical Response of Bone to the Cessation of Exercise: Development ofa Mechanical Test Apparatus for Trabecular Bone

对于临床骨科手术来说，确定骨骼对停止运动的反应至关重要，因为这种负荷条件的变化通常发生在日常生活中。了解这种反应的机理，对基础生物力学和工程设计也有重要意义。先前的研究表明，未成年大鼠胫骨的机械性能通过跑步得到改善。此外，改善的性能在负荷恢复正常后保持不变。16周龄Wistar雌性大鼠分为跑步组（Run）、跑步+久坐组（Run/Sed）和对照组（Control）。Run组大鼠进行1.6km/h，1h/d，6d/周的跑台运动，持续15周。Run/Sed组大鼠进行相同的跑步程序，持续15周。对照组大鼠正常使用 ...更多信息 在整个实验期间不限制活动。处死后，对从每个胫骨中段获得的样本进行压缩和硬度测试。利用X线μCT系统观察胫骨近端的显微结构。与对照组相比，Run组在3周时的破坏压缩载荷较低，但在15周时增加到对照水平。Run组和Run/Sed组的显微维氏硬度略高于Control组。Run组皮质骨和松质骨面积均小于Control组。停止跑步后，即使在30周时，骨小梁的面积仍然较小;然而，皮质骨的面积在30周时增加到对照水平。为了评价骨小梁的力学性能，设计并研制了一种弯曲试验装置。弯曲试验中与松质骨接触的装置边缘部分由不锈钢（SUS 304）制成，环形载荷传感器由铝合金制成。猪胫骨的初步试验表明，它是可能的，使用所开发的设备进行三点弯曲试验。近端骨小梁的弹性模量约为72 MPa。总之，在成熟大鼠胫骨中，通过15周的跑步，材料性能略有增加，结构性能略有下降。从活动状态转为静止状态后，材料性能基本不变。利用研制的装置进行骨小梁的三点弯曲试验是可行的。这项技术将用于骨重建的进一步研究

It is crucial for clinical orthopaedic surgery to determine the response of bone to the cessation of exercise, because such a change in load condition normally happens in daily lives. It is also important for basic biomechanic's and engineering design to understand the mechanism of the response. Previous studies have shown that the mechanical properties of the tibia from immature rats were improved by running. In addition, the improved properties remained unchanged after the return of load to normal. The present study was performed to know whether the same phenomena were observed also in mature ratsSixteen-week-old mature Wistar female rats were divided into running (Run), running and sedentary(Run/Sed), and Control groups. The rats of Run group were subjected to 1.6 km/h, 1 hour-a-day, 6 days-a-week treadmill running program for up to 15 weeks. The rats of Run/Sed group,were subjected to the same running program for up to another 15 weeks. Control group rats were subjected to normal u … More nrestricted activities throughout experimental periods. After sacrifice, compression and hardness tests were performed on the specimens obtained from the midshaft of each tibia. The microstructure of the proximal tibia was also observed using an X-ray μCT system. Compressive load at failure was lower in Run group at 3 weeks as compared with that in Control group, although it increased to a control level at 15 weeks. Micro Vickers hardness in Run and Run/Sed groups was slightly higher than that in Control group. The areas of cortical and trabecular bones were smaller in Run group than those in Control group. After the cessation of running, the area of trabecular bone was remained smaller even at 30 weeks; however, the area of cortical bone increased to a control level at 30 weeks. For the evaluation of the mechanical property oftrabecular bones, a bending test apparatus was designed and developed. The edge parts of the apparatus which contact with the trabecular bone in bending test were consisted of stainless steel (SUS304), and a ring-shaped load transducer was consisted of aluminum alloy. A preliminary test for a pig tibia revealed that it was possible to perform three-point bending test using the developed apparatus. The elastic modulus of the trabecular bone was approximately 72 MPa in proximal areaIn summary, in mature rat tibiae the material properties were slightly increased, and the structural properties were slightly decreased by running for 15 weeks. The material properties were unchanged after the activity change to sedentary state. It is possible using the developed apparatus to perform the three-point bending test for the trabecular bones. This technique will be used in further studies on bone remodeling Less