Changes in trabecular micro-architecture are key to our understanding of osteoporosis. Previous work focusing on structure model index (SMI) measurements have concluded that disease progression entails a shift from plates to rods in trabecular bone, but SMI is heavily biased by bone volume fraction. As an alternative to SMI, we proposed the ellipsoid factor (EF) as a continuous measure of local trabecular shape between plate-like and rod-like extremes. We investigated the relationship between EF distributions, SMI and bone volume fraction of the trabecular geometry in a murine model of disuse osteoporosis as well as from human vertebrae of differing bone volume fraction. We observed a moderate shift in EF median (at later disease stages in mouse tibia) and EF mode (in the vertebral samples with low bone volume fraction) towards a more rod-like geometry, but not in EF maximum and minimum. These results support the notion that the plate to rod transition does not coincide with the onset of bone loss and is considerably more moderate, when it does occur, than SMI suggests. A variety of local shapes not straightforward to categorize as rod or plate exist in all our trabecular bone samples.

小梁微结构的变化是我们了解骨质疏松症的关键。先前关注结构模型指数 (SMI) 测量的工作得出的结论是，疾病进展需要小梁骨从板向棒的转变，但 SMI 严重受骨体积分数的影响。作为 SMI 的替代方案，我们提出了椭球因子 (EF) 作为板状和棒状极端之间局部小梁形状的连续测量。我们研究了废用性骨质疏松症小鼠模型以及不同骨体积分数的人类椎骨中 EF 分布、SMI 和小梁几何形状的骨体积分数之间的关系。我们观察到 EF 中位数（在小鼠胫骨的疾病后期）和 EF 模式（在骨体积分数较低的椎骨样本中）向更棒状的几何形状适度转变，但 EF 最大值和最小值没有变化。这些结果支持这样的观点，即板到棒的转变并不与骨质流失的发生同时发生，并且当发生时，其转变比 SMI 所建议的要温和得多。我们所有的小梁骨样本中都存在多种局部形状，无法直接归类为杆状或板状。