Improved bone structure and strength after long-term mechanical loading is greatest if loading is separated into short bouts
Improved bone structure and strength after long-term mechanical loading is greatest if loading is separated into short bouts
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DOI：
10.1359/jbmr.2002.17.8.1545
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发表时间：
2002-08-01
影响因子：
6.2
通讯作者：
Turner, CH
中科院分区：
文献类型：
--
作者：
Robling, AG;Hinant, FM;Turner, CH
机械负荷对骨细胞具有很强的成骨刺激作用，但骨细胞对机械刺激迅速失敏。在细胞能够有效地传递未来的机械信号之前，必须进行再敏化。以前的实验表明，如果将负荷周期分成几个离散的回合，相隔几个小时，机械负荷方案比在单一的不间断回合中应用周期更具成骨作用。我们研究了16周后不同的机械负荷对大鼠尺骨结构和生物力学性能的影响。26只成年雌性大鼠右侧尺骨承受360次/d的载荷循环，以17N的峰值力以半正弦波形传递，每周3d，持续16周。其中一半的动物(n=13)在一次不间断的比赛(360×1)中接受所有360个每日周期的治疗，另一半(90×4)每天接受4次90个周期的治疗，每次比赛间隔3h。实验包括无负荷基线对照(BLC)组和年龄匹配对照(AMC)组(n=9/组)。死亡后收集以下测量数据：尺骨中段的原位机械应变；尺骨长度；沿整个尺骨长度(1 Mm)的最大和最小第二面积矩(I-Max和I-min)。增量)；以及极限力、破坏能量和整个尺骨的刚度。从微计算机断层扫描(MU(CT))切片重建的全骨图像进行骨形态的定性观察。按360XI和90X4两种加载方式加载，极限载荷分别提高了和87%，破坏能量分别提高了94%和165%，I-MAX分别提高了13%和26%(中远端)，I-min分别提高了69%和96%(中远端)，峰值机械应变分别降低了40%和36%。尽管面骨密度(ABMD)和骨矿含量(BMC)的增幅很低，但生物力学性能仍有很大提高。与单次加载(360×1)相比，机械加载在按恢复期(90×4时间表)分开的不同回合中施加更有效地增强骨的生物力学和结构性能。如果新骨形成定位于生物力学上最相关的部位，如在负荷诱导骨形成过程中发生的，骨密度和骨矿物质的适度增加可以显著改善生物力学特性。
Mechanical loading presents a potent osteogenic stimulus to bone cells, but bone cells desensitize rapidly to mechanical stimulation. Resensitization must occur before the cells can transduce future mechanical signals effectively. Previous experiments show that mechanical loading protocols are more osteogenic if the load cycles are divided into several discrete bouts, separated by several hours, than if the cycles are applied in a single uninterrupted bout. We investigated the effect of discrete mechanical loading bouts on structure and biomechanical properties of the rat ulna after 16 weeks of loading. The right ulnas of 26 adult female rats were subjected to 360 load cycles/day, delivered in a haversine waveform at 17 N peak force, 3 days/week for 16 weeks. One-half of the animals (n = 13) were administered all 360 daily cycles in a single uninterrupted bout (360 X 1); the other half were administered 90 cycles four times per day (90 X 4), with 3 h between bouts. A nonloaded baseline control (BLC) group and an age-matched control (AMC) group (n = 9/group) were included in the experiment. The following measurements were collected after death: in situ mechanical strain at the ulna midshaft; ulnar length; maximum and minimum second moments of area (I-MAX and I-MIN) along the entire length of the ulnas (1-mm. increments); and ultimate force, energy to failure, and stiffness of whole ulnas. Qualitative observations of bone morphology were made from whole bone images reconstructed from microcomputed tomography (mu(CT)) slices. Loading according to the 360 X I and 90 X 4 schedules improved ultimate force by 64% and 87%, energy to failure by 94% and 165%, I-MAX by 13% and 26% (in the middistal diaphysis), I-MIN by 69% and 96% (in the middistal diaphysis), and reduced peak mechanical strain by 40% and 36%, respectively. The large increases in biomechanical properties occurred despite very low 5-12% gains in areal bone mineral density (aBMD) and bone mineral content (BMC). Mechanical loading is more effective in enhancing bone biomechanical and structural properties if the loads are applied in discrete bouts, separated by recovery periods (90 X 4 schedule), than if the loads are applied in a single session (360 X 1). Modest increases in aBMD and BMC can improve biomechanical properties substantially if the new bone formation is localized to the most biomechanically relevant sites, as occurs during load-induced bone formation.