Raab-Cullen D M, Akhter M P, Kimmel D B, Recker R R
Osteoporosis Research Center, Creighton University, Omaha, Nebraska.
J Bone Miner Res. 1994 Aug;9(8):1143-52. doi: 10.1002/jbmr.5650090803.
The rat tibia four-point bending model is a new mechanical loading model in which force is applied through external pads to the rat lower limb. The advantages of the model are controlled force application to a well-defined bone, noninvasive external loading, and the addition of loads to normal daily activity. A disadvantage of the model is that the pads create local pressure on the leg at the contact sites. This study examined the differences in tibial response to bending strains and to local pressure under the pads. A total of 30 adult Sprague-Dawley rats were randomized into three external loading groups: bending, cyclic pressure, and static pressure. The right leg of each rat was externally loaded to create either bending or local pressure without bending; the left leg served as a control. Strains on the lateral surface averaged 1200 mu epsilon in compression during bending load application and < 200 mu epsilon in compression during pressure loading. Histomorphometric data were collected from three regions: the maximal bending region, under the loading pads, and outside the maximal bending region. In the maximal bending region, bending loads created greater mineral apposition rate (MAR) on the lateral surface and greater MAR and formation surface on the medial surface of loaded than control tibiae. The region under the bending pad was exposed to similar bending strains and showed the same pattern of increased MAR as sections from the maximal bending region. Cyclic pressure had no effect on periosteal MAR or formation surface. Static pressure increased MAR only on the lateral tibial surface. Bending stimulates bone formation in regions with the highest bending strains. Similar forces applied only in the form of pressure loading do not stimulate tibial formation either at the contact site or between loading pads. These results suggest that externally applied forces of moderate magnitude stimulate bone formation primarily as a result of increased bending strains, not local pressure at the contact site.
大鼠胫骨四点弯曲模型是一种新的机械加载模型，通过外部垫板对大鼠下肢施加力。该模型的优点是能将力精确施加到明确的骨骼上，采用非侵入性外部加载方式，并在正常日常活动基础上增加负荷。该模型的一个缺点是垫板在接触部位会对腿部产生局部压力。本研究考察了胫骨对弯曲应变和垫板下局部压力的反应差异。总共30只成年Sprague-Dawley大鼠被随机分为三个外部加载组：弯曲组、循环压力组和静态压力组。每只大鼠的右腿进行外部加载以产生弯曲或仅产生局部压力而不产生弯曲；左腿作为对照。在施加弯曲载荷时，外侧表面的应变平均为1200微应变压缩，在施加压力载荷时压缩应变小于200微应变。从三个区域收集组织形态计量学数据：最大弯曲区域、加载垫板下方区域以及最大弯曲区域之外。在最大弯曲区域，与对照胫骨相比，弯曲载荷在外侧表面产生更高的矿物质沉积率（MAR），在内侧表面产生更高的MAR和形成表面。弯曲垫板下方区域承受相似的弯曲应变，并且与最大弯曲区域的切片显示出相同的MAR增加模式。循环压力对骨膜MAR或形成表面没有影响。静态压力仅增加胫骨外侧表面的MAR。弯曲刺激最高弯曲应变区域的骨形成。仅以压力加载形式施加的类似力在接触部位或加载垫板之间不会刺激胫骨形成。这些结果表明，适度大小的外部施加力主要由于弯曲应变增加而非接触部位的局部压力来刺激骨形成。
