Imaging Laboratories, Robarts Research Institute,Schulich School of Medicine and Dentistry, The University of Western Ontario, London, Ontario, Canada.
Bone. 2011 Mar 1;48(3):639-46. doi: 10.1016/j.bone.2010.11.010. Epub 2010 Nov 18.
To investigate the role of intra-osseous lesions in advancing the pathogenesis of Osteoarthritis (OA) of the knee, using Finite Element Modeling (FEM) in conjunction with high-resolution imaging techniques.
Twenty early stage OA patients (≤ Grade 2 radiographic score) were scanned with a prototype, cone-beam CT system. Scans encompassed the mid-shaft of the femur to the diaphysis of the proximal tibia. Individual bones were segmented to create 3D geometric models that were transferred to FE software for loading experiments. Patient-specific, inhomogeneous material properties were derived from the CT images and mapped directly to the FE models. Duplicate models were also created, with a 3D sphere (range 3-12 mm) introduced into a weight-bearing region of the joint, mimicking the size, location, and composition of a subchondral bone cyst (SBC). A spherical shell extending 1mm radially around the SBC served as the sample volume for measurements of von Mises equivalent stress. Both models were vertically loaded with 750 N, or approximately 1 body weight during a single-leg stance.
All FE models exhibited a physiologically realistic weight-bearing distribution of stress, which initiated at the joint surface and extended to the cortical bone. Models that contained the SBC experienced a nearly two-fold increase in stress (0.934 ± 0.073 and 1.69 ± 0.159 MPa, for the non-SBC and SBC models, respectively) within the bone adjacent to the SBC. In addition, there was a positive correlation found between the diameter of the SBC and the resultant intra-osseous stress under load (p = 0.004).
Our results provide insights into the mechanism by which SBC may accelerate OA, leading to greater pain and disability. Based on these findings, we feel that patient-derived FE models of the OA knee - utilizing in vivo imaging data - present a tremendous potential for monitoring joint mechanics under physiological loads.
运用有限元建模（FEM）与高分辨率成像技术，探究骨内病变在膝关节骨关节炎（OA）发病机制中的作用。
对 20 例早期 OA 患者（≤ 2 级放射评分）进行原型锥束 CT 系统扫描。扫描范围包括股骨中段至胫骨近端骨干。对各骨进行分割，建立 3D 几何模型，然后将其转移到 FE 软件中进行加载实验。通过 CT 图像得出患者特定的非均匀材料属性，并直接映射到 FE 模型上。还创建了两个模型，一个是在关节承重区域引入一个 3D 球体（范围 3-12mm），模拟出一个软骨下骨囊肿（SBC）的大小、位置和组成；另一个是在 SBC 周围延伸 1mm 半径的球形壳，作为测量 von Mises 等效应力的样本体积。两个模型均垂直加载 750N，相当于单腿站立时的 1 个体重。
所有 FE 模型均表现出生理上真实的承重应力分布，从关节表面延伸到皮质骨。包含 SBC 的模型在靠近 SBC 的骨内的应力增加了近两倍（非 SBC 和 SBC 模型分别为 0.934 ± 0.073 和 1.69 ± 0.159MPa）。此外，SBC 的直径与加载时骨内的内源性应力之间存在正相关（p = 0.004）。
我们的研究结果提供了有关 SBC 如何加速 OA 发展的机制的深入了解，导致更大的疼痛和残疾。基于这些发现，我们认为利用体内成像数据的 OA 膝关节患者衍生的 FE 模型具有监测生理负荷下关节力学的巨大潜力。
