Mosley J R, Lanyon L E
Department of Veterinary Basic Sciences, The Royal Veterinary College, London, UK.
Bone. 1998 Oct;23(4):313-8. doi: 10.1016/s8756-3282(98)00113-6.
To test the hypothesis that the rate of change of strain to which a bone is subjected is an important determinant to the subsequent functionally adaptive modeling response, the ulnae of growing male rats were subjected to dynamic axial loading in vivo for a short period each day over 2 weeks. Due to the longitudinal curvature of the ulna, such axial loading leads to both compression and bending. The left ulna in three groups of rats was loaded cyclically between 1 and 20 N in a trapezoidal pattern to produce dynamic, longitudinal compressive strains of -0.004 (-4000 microstrain) at the medial midshaft with one of three strain rates: low (+/-0.018 sec(-1); n = 7); moderate (+/-0.030 sec(-1); n = 7); and high (+/-0.100 sec(-1); n = 8). These strain rates span the range recorded from strain gauges bonded to the bone at this site during a variety of normal activities. At the end of the experiment, the loaded ulnae were slightly, but significantly, shorter than their contralateral controls (2.7% to 5.6% mean change in length; p < 0.0001). This effect was most marked at lower strain rates, associated with an increased load-bearing time. The pattern of adaptive modeling along the bone shaft was similar for all groups, each showing a reduced rate of periosteal expansion proximally, and increased periosteal new bone production distally. This distal increase was achieved through enhanced periosteal bone formation on the lateral (tension) cortex, and arrest of resorption, with conversion to formation on the medial (compression) surface. The modeling response to axial loading therefore involves complex location-dependent increases and decreases in both formation and resorption. The high-strain-rate group demonstrated a 54% greater osteogenic response than the moderate-strain-rate group, which in turn showed a 13% larger response than the low-strain-rate group. Rate of strain change is therefore a major determinant of the adaptive osteogenic/antiresorptive response to mechanical load. Across the physiological range, a high rate of strain change provides a greater osteogenic stimulus than the same peak strain achieved more slowly.
为了验证骨骼所承受应变的变化率是后续功能适应性建模反应的重要决定因素这一假设，对生长中的雄性大鼠的尺骨在体内每天进行短时间的动态轴向加载，持续2周。由于尺骨的纵向弯曲，这种轴向加载会导致压缩和弯曲。三组大鼠的左尺骨以梯形模式在1至20 N之间循环加载，以在中轴内侧产生-0.004（-4000微应变）的动态纵向压缩应变，应变率有三种：低（±0.018秒-1；n = 7）；中（±0.030秒-1；n = 7）；高（±0.100秒-1；n = 8）。这些应变率涵盖了在各种正常活动期间粘贴在该部位骨骼上的应变片记录的范围。实验结束时，加载的尺骨比其对侧对照略短，但差异显著（平均长度变化2.7%至5.6%；p < 0.0001）。这种效应在较低应变率下最为明显，这与增加的承重时间有关。所有组沿骨干的适应性建模模式相似，每组均显示近端骨膜扩张率降低，远端骨膜新骨生成增加。这种远端增加是通过外侧（张力）皮质上骨膜骨形成增强以及吸收停止，并在内侧（压缩）表面转化为形成来实现的。因此，对轴向加载的建模反应涉及形成和吸收在位置上复杂的增加和减少。高应变率组的成骨反应比中应变率组大54%，而中应变率组又比低应变率组大13%。因此，应变变化率是对机械负荷的适应性成骨/抗吸收反应的主要决定因素。在生理范围内，高应变变化率比以较慢速度达到的相同峰值应变提供更大的成骨刺激。
