Al-sukhun Jehad, Penttilä Heikki, Ashammakhi Nureddin
Department of Oral and Maxillofacial Surgery, Euro Oral Hammaslääkärikeskus Oy, Helsinki, Finland.
J Craniofac Surg. 2012 May;23(3):669-74. doi: 10.1097/SCS.0b013e31824db8a0.
The progress in computer technology and the increased use of finite element analysis in the medical field by nonengineers and medical researchers lead us to believe that there is a need to develop a systematic approach to validate a finite element model (FEM), of a human orbit, that simulates part of the maxillofacial skeleton and to investigate the effects and the clinical significance of changing the geometry, boundary conditions, that is, muscle forces, and orthotropic material properties on the predictive outcome of an FEM of a human orbit.
Forty-seven variables affecting the material properties, boundary conditions, and the geometry of an FEM of a human orbit including the globe were systematically changed, creating a number of FEMs of the orbit. The effects of the variations were quantified as differences in the principal strain magnitudes modeled by the original FEM (criterion standard), before the sensitivity analyses, and those generated by the changed FEMs.
The material properties that had the biggest impact on the predicted principal strains were the shear moduli (up to 21%) and the absence of fatty tissue (up to 75%). The boundary condition properties that had the biggest impact on the predicted principal strains were the superior rectus muscle and canthal ligaments (up to 18% and 23%, respectively). Alterations to the geometry of the orbit, such as an increase in its volume, had the greatest effect on principal strain magnitudes (up to 52%).
Changes in geometry, boundary conditions, and orthotropic material properties can induce significant changes in strain patterns. These values must therefore be chosen with care when using finite element modeling techniques. This study also highlights the importance of restoring the orbital fat and volume when reconstructing the orbital floor following a blunt injury. The possibility that the unrestored increase in the orbital volume and the resulting stresses may be a source of globe injuries, causing diplopia, cannot be excluded.
计算机技术的进步以及非工程师和医学研究人员在医学领域对有限元分析的更多应用，使我们相信有必要开发一种系统方法来验证模拟部分颌面骨骼的人体眼眶有限元模型（FEM），并研究改变几何形状、边界条件（即肌肉力）和正交各向异性材料特性对人体眼眶有限元模型预测结果的影响及临床意义。
系统地改变影响包括眼球在内的人体眼眶有限元模型的材料特性、边界条件和几何形状的47个变量，创建多个眼眶有限元模型。将这些变化的影响量化为在敏感性分析之前由原始有限元模型（标准模型）模拟的主应变大小与改变后的有限元模型产生的主应变大小之间的差异。
对预测主应变影响最大的材料特性是剪切模量（高达21%）和无脂肪组织（高达75%）。对预测主应变影响最大的边界条件特性是上直肌和眦韧带（分别高达18%和23%）。眼眶几何形状的改变，如体积增加，对主应变大小影响最大（高达52%）。
几何形状、边界条件和正交各向异性材料特性的变化可引起应变模式的显著变化。因此，在使用有限元建模技术时必须谨慎选择这些值。本研究还强调了钝性损伤后重建眶底时恢复眶脂肪和体积的重要性。不能排除未恢复的眶体积增加及其产生的应力可能是眼球损伤导致复视的一个原因。
