近端股骨尸制备基于CT的断裂强度测试和定量的有限元分析
Summary
我们提出了如何妥善保存，并准备测试断裂和定量计算机断层成像尸体股骨一个强大的协议。该方法提供了对用于确定骨矿物密度，断裂强度之间的关系，并限定有限元模型的几何形状和性能的目的输入条件的精确控制。
Abstract
尸体断裂测试通常用来了解影响股骨近端强度的因素。由于体外生物组织很容易随着时间的推移失去其机械性能，样品必须仔细进行实验测试的准备，以获得在体内条件代表可靠的结果。出于这个原因，我们设计了一个协议和一套夹具以制备股骨标本，使得它们的机械性能经历最小的变化。在准备步骤和机械测试除股骨保持在冷冻状态。有临床双能X线骨密度仪（DXA）骨密度仪获得了全髋关节和股骨颈骨密度（BMD）的相关临床措施，并利用CT与校准幻影，获得三维几何和骨矿物质的分布基于所述灰度值的定量估计。任何可能的骨骼疾病，骨折，或植入物或影响骨结构的工件的情况下，被排除用X射线扫描。对于制备，所有的骨头被仔细清洗过量的软组织，并切断与盆栽在感兴趣的内部旋转角度。切割夹具允许骨的远端被切断而使股骨近端在所希望的长度。以允许以后的CT扫描和机械测试期间在规定的角度股骨颈定位，股骨近端的轴是在聚甲基丙烯酸甲酯（PMMA），使用专为所需的方向而设计的夹具盆栽。然后从我们的实验中收集的数据被用于定量计算机断层扫描（QCT）的验证为基础的有限元分析（FEA），如在不同的协议描述。在这个手稿中，我们提出了力学性能试验和随后的QCT / FEA建模精确的骨骼制备的协议。目前的协议已成功应用于准备约200 CADaveric股骨超过6年的时间。
Introduction
Determining the true cadaveric proximal femoral fracture strength with mechanical testing is a destructive method that requires a rigorous testing approach for accurate measurements. In particular, proper bone preparation methods are necessary to maintain near in vivo integrity of the bones prior to mechanical fracture testing1. This is achieved by proper bone storage and minimizing handling at room temperature. This test data is extensively used to validate QCT/FEA models of femoral fracture which have the potential to be used clinically to understand the fracture risk, especially in osteoporotic patients. Unfortunately, there is no current standard procedure to prepare proximal femur samples for mechanical testing. A good testing procedure should ensure repeatability and reproducibility of the preparation process. Therefore, fixtures required for sample preparation need to be carefully designed and fabricated to minimize the likelihood of various testing errors. We also need to minimize the preparation time for which bone tissue is at room temperature and thus in danger of degradation with irreversible changes in mechanical properties.
To this end, we have developed a procedure that preserves bone tissue across multiple preparation steps. This is important to ensure minimal exposure time at room temperature while also minimizing the number of freeze/thaw cycles which can affect tissue physical properties2. The entire procedure is long and nontrivial as the steps occurred over multiple weeks and required scheduling for scanning procedures and personnel availability. The steps included thawing bone samples, screening the samples using DXA scanning to obtain bone mineral density (BMD) values, X-ray to rule out any diseased specimens, and finally CT scanning to estimate distribution of bone mineral and femoral geometry. All the specimens were prepared for testing by removing extraneous soft tissues from the bone surface, cutting the femur to a length required for testing, and potting the femur in a desired orientation for simulating a sideways fall on the hip during subsequent testing. It is essential to keep the time period for all these operations as short as possible. A robust protocol is thus mandatory for consistent specimen preparation, tissue preservation between steps, and for reducing the overall preparation time.
The aim of this paper is to present in detail the procedures involved in the preparation of femoral samples for subsequent mechanical testing under various conditions. Preservation of the bone tissue is crucial in this process and we achieved it by keeping specimens frozen between steps and keeping them carefully wrapped in saline saturated towels at all times except when scanning and mechanically testing the bones. Femora were also kept wrapped in saline wet towels during the steps involving PMMA curing to prevent dryness of the bone tissue.
Protocol
Representative Results
Discussion
我们提出了确保臀部配置横盘下跌股力量力学测试和QCT / FEA建模一个强大的骨骼准备协议。这种方法成了我们的标准的内部协议。在6年的过程中，有不同的人员，成功制备出约200股骨下此协议。该协议的成果包括分类使用DXA骨条件下，排除了转移性疾病，先前的骨折，或利用X射线的植入物，并获得矿物分布和利用CT用于随后QCT / FEA建模的3D几何形状。切割，灌封，并且扫描装置被设计成容纳左和?…
Disclosures
The authors have nothing to disclose.
Acknowledgements
我们要感谢的材料和结构试验核心设施梅奥诊所寻求技术支持。此外，我们要感谢遵义伯格伦德，布兰特纽曼，乔恩运书房Buijs，博士，在研究过程中他们的帮助。这项研究是由财政从格兰杰基金会格兰杰创新基金的支持。
Materials
| CT potting container and scanning fixture | Internally manufactured | N/A | Custom designed and manufactured |
| CT scanner | Siemens | Somatom Definition scanner (Siemens, Malvern, PA) | CT scanning equipment |
| Quantitative CT Phantom | Midways Inc, San Francisco, CA | Model 3 CT calibration Phantom | Used for obtaining BMD values from Hounsfield units in the CT image |
| Dual Energy X-ray Absorptiometry scanner | General Electric | N/A | GE Lunar iDXA scanner for bone health or any similar BMD scanners |
| Hygenic Orhodontic Resin (PMMA) | Patterson Dental Supply | H02252 | Controlled substance and can be purchased with proper approval |
| Freezer | Kenmore | N/A | This is a -20oC storage for bones |
| X-ray scanner | General Electric | 46-270615P1 | X-ray imaging equipment. |
| X-ray films | Kodak | N/A | Used to display x-ray images |
| X-ray developer | Kodak X-Omatic | M35A X-OMAT | Used for developing X-ray images |
| X-ray Cassette | Kodak X-Omatic | N/A | Used for holding x-ray films |
| 5-pound Rice Bags | Great Value | N/A | Used for mimicking soft tissue during the DXA scanning process |
| Physiologic Saline (0.9% Sodium Chloride) | Baxter | NDC 0338-0048-04 | Used for keeping samples hydrated |
| Scalpels and scrapers | Bard-Parker | N/A | Used to clean the bone from soft tissue |
| Cast cutter | Stryker | 810-BD001 | Used to cut femoral shaft |
| Drilling machine | Bosch | N/A | Used to drill the femoral shaft |
| Fume Hood | Hamilton | 70532 | Used for ventilation when using making PMMA |
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