Structure Model Index Does Not Measure Rods and Plates in Trabecular Bone.
Structure Model Index Does Not Measure Rods and Plates in Trabecular Bone.
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DOI：
10.3389/fendo.2015.00162
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发表时间：
2015
影响因子：
5.2
通讯作者：
Doube M
中科院分区：
文献类型：
--
作者：
Salmon PL;Ohlsson C;Shefelbine SJ;Doube M
结构模型指数（SMI）被广泛应用于骨小梁内棒和板的测量。它利用了当结构从球形（SMI = 4）到圆柱形（SMI = 3）到平面（SMI = 0）变化时发生的表面曲率变化。SMI最重要的假设是整个骨表面是凸的，并且表面上所有点的曲率微分都是正的。小梁连续体内复杂的连接表明，很大一部分表面可能是凹的，违反了凸性的假设，并产生负微分区域。我们在BoneJ插件中实现了SMI，包括测量表面网格扩张后面积增加或减少的表面数量的能力，以及可视化凹和凸区域的能力。我们测量了SMI及其阳性（SMI+）和阴性（SMI -）成分，骨体积分数（BV/TV），表面凹的比例（CF）和平均椭球因子（EF）在小梁骨使用38 x射线微断层扫描（XMT）图像从一个大鼠卵巢切除术的性类固醇挽救骨质丢失模型，和169 XMT图像从广泛选择的87种股骨（哺乳动物，鸟类和鳄鱼）。我们通过对大象小梁图像的侵蚀模拟骨吸收，并记录每个侵蚀阶段的SMI和BV/TV。高达70%，很少小于20%的小梁表面是凹的（CF 0.155-0.700）。SMI不可避免地受到SMI−引起的像差的影响，而SMI−与BV/TV和CF密切相关。由于SMI和BV/TV之间的密切和人为的关系，骨丢失中的板到棒的转变是一种错误的观察结果。SMI不能区分哺乳动物和鸟类骨骼的独特的小梁几何形状，而EF可以清楚地检测到鸟类的片状小梁。EF与BV/TV和CF没有混淆关系。文献中报道的SMI结果应持怀疑态度。我们建议使用EF代替SMI来测量小梁骨棒和钢板。
Structure model index (SMI) is widely used to measure rods and plates in trabecular bone. It exploits the change in surface curvature that occurs as a structure varies from spherical (SMI = 4), to cylindrical (SMI = 3) to planar (SMI = 0). The most important assumption underlying SMI is that the entire bone surface is convex and that the curvature differential is positive at all points on the surface. The intricate connections within the trabecular continuum suggest that a high proportion of the surface could be concave, violating the assumption of convexity and producing regions of negative differential. We implemented SMI in the BoneJ plugin and included the ability to measure the amounts of surface that increased or decreased in area after surface mesh dilation, and the ability to visualize concave and convex regions. We measured SMI and its positive (SMI+) and negative (SMI−) components, bone volume fraction (BV/TV), the fraction of the surface that is concave (CF), and mean ellipsoid factor (EF) in trabecular bone using 38 X-ray microtomography (XMT) images from a rat ovariectomy model of sex steroid rescue of bone loss, and 169 XMT images from a broad selection of 87 species’ femora (mammals, birds, and a crocodile). We simulated bone resorption by eroding an image of elephant trabeculae and recording SMI and BV/TV at each erosion step. Up to 70%, and rarely <20%, of the trabecular surface is concave (CF 0.155–0.700). SMI is unavoidably influenced by aberrations induced by SMI−, which is strongly correlated with BV/TV and CF. The plate-to-rod transition in bone loss is an erroneous observation resulting from the close and artifactual relationship between SMI and BV/TV. SMI cannot discern between the distinctive trabecular geometries typical of mammalian and avian bone, whereas EF clearly detects birds’ more plate-like trabeculae. EF is free from confounding relationships with BV/TV and CF. SMI results reported in the literature should be treated with suspicion. We propose that EF should be used instead of SMI for measurements of rods and plates in trabecular bone.