Roux Jean-Paul, Boutroy Stéphanie, Bouxsein Mary L, Chapurlat Roland, Wegrzyn Julien
INSERM UMR 1033, Université de Lyon, Lyon, France.
Orthopedic Biomechanics Laboratory, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA.
Bone Rep. 2020 Sep 15;13:100716. doi: 10.1016/j.bonr.2020.100716. eCollection 2020 Dec.
Beside areal bone mineral density (aBMD), evaluation of fragility fracture risk mostly relies on global microarchitecture. However, microarchitecture is not a uniform network. Therefore, this study aimed to compare local structural weakness to global microarchitecture on whole vertebral bodies and to evaluate how local and global microarchitecture was associated with bone biomechanics.
From 21 human L3 vertebrae, aBMD was measured using absorptiometry. Parameters of global microarchitecture were measured using HR-pQCT: trabecular bone volume fraction (Tb.BV/TV), trabecular number, structure model index and connectivity density (Conn.D). Local minimal values of aBMD and Tb.BV/TV were identified in the total (Tt) or trabecular (Tb) area of each vertebral body. "Two dimensional (2D) local structural weakness" was defined as Tt.BMD, Tt.BV/TV and Tb.BV/TV. Mechanical testing was performed in 3 phases: 1/ initial compression until mild vertebral fracture, 2/ unloaded relaxation, and 3/ second compression until failure.
Initial and post-fracture mechanics were significantly correlated with bone mass, global and local microarchitecture. Tt.BMD, Tt.BV/TV, Tb.BV/TV, and initial and post-fracture mechanics remained significantly correlated after adjustment for aBMD or Tb.BV/TV ( < 0.001 to 0.038). The combination of the most relevant parameter of bone mass, global and local microarchitecture associated with failure load and stiffness demonstrated that global microarchitecture explained initial and post-fracture stiffness, while local structural weakness explained initial and post-fracture failure load ( < 0.001).
Local and global microarchitecture was associated with different features of vertebral bone biomechanics, with global microarchitecture controlling stiffness and 2D local structural weakness controlling strength. Therefore, determining both localized low density and impaired global microarchitecture could have major impact on vertebral fracture risk prediction.
除了区域骨矿物质密度（aBMD）外，脆性骨折风险评估主要依赖于整体微观结构。然而，微观结构并非均匀的网络。因此，本研究旨在比较整个椎体上局部结构弱点与整体微观结构，并评估局部和整体微观结构如何与骨生物力学相关联。
从21个人类L3椎体中，使用骨密度测定法测量aBMD。使用高分辨率外周定量CT（HR-pQCT）测量整体微观结构参数：小梁骨体积分数（Tb.BV/TV）、小梁数量、结构模型指数和连通性密度（Conn.D）。在每个椎体的总体（Tt）或小梁（Tb）区域中确定aBMD和Tb.BV/TV的局部最小值。“二维（2D）局部结构弱点”定义为Tt.BMD、Tt.BV/TV和Tb.BV/TV。力学测试分三个阶段进行：1/初始压缩直至轻度椎体骨折，2/卸载松弛，3/第二次压缩直至破坏。
初始和骨折后力学与骨量、整体和局部微观结构显著相关。在调整aBMD或Tb.BV/TV后，Tt.BMD、Tt.BV/TV、Tb.BV/TV以及初始和骨折后力学仍显著相关（<0.001至0.038）。与破坏载荷和刚度相关的骨量、整体和局部微观结构最相关参数的组合表明，整体微观结构解释了初始和骨折后刚度，而局部结构弱点解释了初始和骨折后破坏载荷（<0.001）。
局部和整体微观结构与椎体骨生物力学的不同特征相关，整体微观结构控制刚度，二维局部结构弱点控制强度。因此，确定局部低密度和整体微观结构受损都可能对椎体骨折风险预测产生重大影响。
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