TOWARD PATIENT SPECIFIC DENSITY MODELLING OF THE TIBIA

针对患者特定胫骨的密度建模

• 批准号: 7723423
• 负责人: Thomas Impelluso
• 金额: $ 0.05万
• 依托单位: CARNEGIE-MELLON UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-08-01 至 2009-07-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7723423
• 关键词: Algorithms; Biomechanics; Body Weight; Cellular Mechanotransduction; Clinical; Code; Computer Retrieval of Information on Scientific Projects Database; Computing Methodologies; Condition; Distal; Elements; Etiology; Fatigue; Female; Femur; Finite Element Analysis; Fracture; Frequencies; Funding; Gait; Generic Drugs; Genetic; Grant; Imaging Techniques; Individual; Institution; Intercellular Fluid; Lateral; Laws; Lead; Left; Length; Mechanics; Medial; Mediating; Modeling; Numbers; Pathology; Patient Care; Patients; Peripheral; Radiation Dosage; Ramp; Rate; Research; Research Personnel; Resources; Running; Scanning; Source; Stress; Stress Fractures; Students; Surface; Thick; Time; United States National Institutes of Health; Update; Work; X-Ray Computed Tomography; abstracting; base; bone; bone epiphysis; bone quality; clinical application; density; field study; fluid flow; improved; novel; simulation; three-dimensional modeling; tibia

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. (We are requesting an expedited review. I conducted this work with my graduate student, Charles Negus, and during the break, we would like to do one more run in anticipation of a new project. The abstract is below: While mechanobiological bone research begins at or below the cellular level, it finds its ultimate application in improving patient care in a clinical setting. A crucial field of study in bridging the gap between the cellular level research and clinical application is computational mechanics. Stress fracture formation is a mechanically mediated pathology that has the potential to be directly aided by advances in computational methods and mechanobiological research. Stress fracture etiology seems to be a highly patient-specific interplay of bone loads arising from an individuals biomechanics, bone geometry, and bone quality. Bone geometry and quality will inherently reflect both genetic influences and prior functional adaptation. Repeated loads to the bone result in fatigue-like damage accumulation, particularly in highly mineralized, brittle bone where small cracks coalesce into stress fractures under repeated loading [1]. Local remodeling around the fracture which attempts to clear the damage, if it occurs in the presence of continued loading, can actually exacerbate the problem. Assessing an individuals stress fracture potential thus entails assessing their bone quality as well as their peak stresses under repeated loads. Estimating a subjects tibial stress profile suggests a patient-specific finite element analysis, whose geometry is ideally based on low radiation dosage, noninvasive imaging techniques. Assigning trabecular and cortical density distributions to this model present other challenges. We have previously described a novel, but computationally simple approach to density redistribution and orthotropic material alignment [2]. Dynamic Hypoelastic Remodeling is inspired by current understanding of cellular mechanotransduction as being predicated on interstitial fluid flow resulting from dynamic loading. The remodeling algorithm is incorporated in an explicit, dynamic finite element code parallelized using Message Passing Interface. Remodeling occurs at discrete, periodically occurring time steps. Cortical and trabecular apparent densities are updated based on local strain rate, and realignment of principal material directions is driven by the local stress tensor. Stress is calculated using a path-dependent hypoelastic constitutive law, formulated with the Jaumann stress rate. Loading conditions were linearized around instants of peak rate of application during normal gait and stair climbing, assumed to occur with sufficient frequency to exceed the threshold cycle number for cellular remodeling activation. Results from simulations involving the proximal femur indicate that a target strain rate for this dynamic approach is |D_I | = 1.7%/sec. Additionally, we apply DHR to patient-specific 3D models of the tibia. Peripheral quantitative computed tomography (pQCT) scans of the left tibia were collected for female subjects at 4%, 38%, and 66% of tibial length. Based on these three scans, approximate 3D models of the entire tibial surface was estimated by extrapolation. Each subject-specific model tibia was assigned generic epiphyses from the Standardized Tibia Project which were scaled according to her anthropometrics. Then the periosteal boundaries of the pQCT scans were imported into the diaphyseal region, and a 3D lofted surface was generated between the epiphyses and pQCT boundaries. The 3D surface was then meshed with trilinear hexahedral elements. The distal end of the tibia was assumed fixed, and five ramped loading conditions, defined based on each subjects body weight, were applied to the medial and lateral articular surfaces. The diaphyseal density distribution predicted by DHR will be compared against the original pQCT scans to assess the predicted cortical thickness against actual thickness. These models can then be used to conduct patient-specific stress analyses which could aid in assessing peak stresses that could lead to stress fracture. This research illustrates how modern cellular research, imaging techniques, and computational methods can be integrated in a manner which has potential clinical practicality.

该副本是利用众多研究子项目之一 由NIH/NCRR资助的中心赠款提供的资源。子弹和 调查员（PI）可能已经从其他NIH来源获得了主要资金， 因此可以在其他清晰的条目中代表。列出的机构是 对于中心，这不一定是调查员的机构。 （我们正在要求加快审查。我与研究生Charles Negus进行了这项工作，在休息期间，我们想在预期的一个新项目中进行更多运行。摘要下面是：机械生物学研究开始或低于细胞级别，它在临床环境中在临床环境中进行了临床范围的临床水平，这是在临床上的最终应用。骨折的形成是一种机械介导的病理学，可以通过计算方法和机械性骨折病因的进步来帮助，这是一个高度患者的骨负荷相互作用。积累，特别是在高度矿化的脆性骨骼中，小裂缝在重复的负荷下凝聚成应激骨折[1]。骨折周围的局部重塑，如果在持续加载的情况下发生损坏，试图清除损坏实际上会加剧问题。评估个体应力骨折潜力，因此需要评估其骨骼质量以及在重复载荷下的峰值应力。估计受试者的胫骨应力曲线表明患者特定的有限元分析，其几何形状理想地基于低辐射剂量，无创成像技术。将小梁和皮质密度分布分配给该模型带来其他挑战。我们先前已经描述了一种新颖但在计算上简单的方法，用于重新分布和正交物质比对[2]。动态低弹性重塑的灵感来自对细胞机械转导的当前理解，因为是基于动态负载引起的间质流体流动。重塑算法纳入使用消息传递接口并行化的显式，动态有限元代码。重塑发生在离散的，定期发生的时间步骤中。根据局部应变率，对皮质和小梁表观密度进行了更新，主材料方向的重新对齐是由局部应力张量驱动的。使用依赖路径依赖性的低弹性定律定律计算应力，该定律以Jaumann应力率制定。在正常步态和楼梯攀爬期间，载荷条件在峰值峰值速率周围线性化，假定发生足够频率以超过细胞重塑激活的阈值周期数。涉及股骨近端的模拟结果表明，这种动态方法的目标应变率为| d_i | = 1.7％/秒。此外，我们将DHR应用于胫骨特异性3D模型。为女性受试者收集了左胫骨的外围定量计算机断层扫描（PQCT）扫描，为4％，38％和66％的胫骨长度。基于这三个扫描，通过外推估计了整个胫骨表面的大约3D模型。每个受试者特异性的胫骨都被分配给标准化胫骨项目的通用表周，根据她的人体测量法进行了缩放。然后将PQCT扫描的骨膜边界进口到diaphyseal区域，并在epiphyses和PQCT边界之间产生3D扁平表面。然后将3D表面与三联六面体元素融合。假定胫骨的远端是固定的，并且根据每个受试者的体重定义了五个坡道的载荷条件，将其应用于内侧和外侧关节表面。将DHR预测的dia射线密度分布与原始PQCT扫描进行比较，以评估预测的皮质厚度与实际厚度。然后，这些模型可用于进行患者特异性的压力分析，这可能有助于评估可能导致胁迫骨折的峰值应力。这项研究说明了现代的细胞研究，成像技术和计算方法如何以具有潜在临床实用性的方式整合。