人髋关节微观结构失效机制的成像
Summary
该协议通过结合大体积显微 CT 扫描、定制的压缩载物台和先进的图像处理工具，能够测量整个人类股骨近端骨微结构的变形及其韧性。
Abstract
在逐渐增加的负荷下对骨骼微观结构进行成像可以观察骨骼的微观结构失效行为。在这里，我们描述了一种方案，用于在逐渐增加的变形下获得整个股骨近端的三维微观结构图像序列，导致股骨颈的临床相关骨折。该方案使用来自人群中骨密度较低端的 66-80 岁女性供体的四个股骨来证明（T 分数范围 = -2.09 至 -4.75）。设计了一个无线电透明的压缩载物台，用于加载复制单腿姿势的标本，同时记录显微计算机断层扫描 （micro-CT） 成像期间施加的载荷。视场宽 146 mm，高 132 mm，各向同性像素尺寸为 0.03 mm。力增量基于断裂载荷的有限元预测。压缩台用于将位移施加到试样上并制定规定的力增量。股骨颈张开和剪切导致的股骨头下骨折发生在四到五次负荷增加后。对显微CT图像和反作用力测量值进行处理，研究骨应变和能量吸收能力。皮层的不稳定性出现在早期的加载步骤中。股骨头软骨下骨在骨折前出现大变形，达到16%，支撑能力逐渐增加直至骨折。变形能随位移直至断裂呈线性增加，而刚度在断裂前降至接近零的值。在最后 25% 的力增量中，试样吸收了四分之三的断裂能量。总之，开发的方案揭示了显着的能量吸收能力或损伤耐受性，以及高龄供体皮质骨和小梁骨之间的协同相互作用。
Introduction
股骨颈骨折是老龄化人口的主要负担。显微计算机断层扫描 （micro-CT） 成像和伴随的机械测试可以观察骨微观结构并研究其与骨强度的关系、与年龄相关的变化以及负荷下的位移 1,2。然而，直到最近，负重骨骼的显微 CT 研究仅限于切除的骨芯3、小动物4 和人类脊柱单元5。本方案可以量化整个近端人股骨微观结构在负荷下和骨折后的位移。
已经进行了几项研究来调查人类股骨的衰竭，有时，这些研究得出了截然不同的结论。例如，与年龄相关的皮质和小梁结构变薄被认为通过引起骨骼的弹性不稳定性来决定与年龄相关的骨折易感性6,7，这与假设没有弹性不稳定性的皮质应变和股骨力量预测的高确定系数形成鲜明对比 （R2 = 0.80-0.97）8,9.然而，这些研究系统地低估了股骨强度（21%-29%），从而对模型 8,10 中实施的脆性和准脆性骨反应提出了质疑。对于这些明显相反的发现，一种可能的解释可能是与孤立的骨芯相比，整个骨骼的骨折行为不同。因此，观察整个股骨近端骨微结构的变形和骨折反应可能会增进对髋部骨折力学和相关应用的了解。
目前以微米分辨率对整个人体骨骼进行成像的方法有限。龙门架和探测器尺寸必须提供合适的工作体积来容纳人体近端股骨（约 13 cm x 10 cm，宽 x 长），并且可能提供 0.02-0.03 mm 量级的像素尺寸，以确保可以捕获相关的微观结构特征11。目前，一些同步加速器设施1和一些市售的大体积显微CT扫描仪12,13可以满足这些规格。压缩阶段必须是无线电透明的，以尽量减少 X 射线衰减，同时产生足以导致人体股骨骨折的力（例如，老年白人女性在 0.9 kN 到 14.3 kN 之间）14。这种较大的断裂荷载变化使断裂荷载步数、总实验时间和相应产生的数据量的规划变得复杂。为了解决这个问题，可以使用临床计算机断层扫描 （CT） 图像1,2 中标本的骨密度分布，通过有限元建模来估计骨折载荷和位置。最后，在实验结束后，需要对产生的大量数据进行处理，以研究整个人体股骨的失效机理和耗能能力。
在这里，我们描述了一种协议，用于在逐渐增加的变形下获得整个股骨近端的三维微观结构图像序列，这导致股骨颈的临床相关骨折2。该协议包括规划标本压缩的逐步增量，通过定制的无线电透明压缩台加载，通过大体积显微CT扫描仪成像，以及处理图像和负载曲线。
Protocol
Representative Results
Discussion
本方案允许在 离体的三维空间中研究髋部骨折的时间经过的微观力学。一种能够对人体股骨近端施加渐进变形并测量反作用力的透射线透明（铝）压缩台已经过定制设计、制造和测试。该协议中采用大体积显微CT扫描仪来提供图像体积的时间序列，以微观分辨率显示整个股骨近端，并逐渐加载。在这项工作中，利用图像的弹性共配准计算了位移场和应变场。该协议能够显示股骨近端微观结?…
Disclosures
The authors have nothing to disclose.
Acknowledgements
澳大利亚研究委员会（FT180100338;IC190100020） 表示感谢。
Materials
| Absorbent tissue | N/A | Maintain the bone moisture throughout the experiment | |
| Alignment rig | Custom-made | Rig for positioning the specimen in the potting cup | |
| Aluminium potting cup | Custom-made | Potting cup | |
| Bone saw | N/A | Cut the specimen to size | |
| Calibration phantom QCT Pro | Mindways Software, Inc., Austin, USA | CT Calibration 13002 | Calibrate grey levels in the images into equivalent bone mineral (ash) density levels |
| Clinical Computed-Tmography scanner | General Electric Medical Systems Co., Wisconsin, USA | Optima CT660 | Preliminary imaging for the prediction of the load step to fracture |
| Compressive stage | Custom-made | A 10 kg, radiotransparent compressive stage for applying and maintaining throught imaging a prescribed deformation to the specimen. | |
| Dental cement | Soesterberg, The Netherlands | Vertex RS | |
| Femur specimen | Science Care, Phoenix, USA | ||
| Finite-element analysis software | ANSYS Inc., Canonsburg, USA | ANSYS Mechanical APDL | Finite-element software package |
| Freezer | N/A | Store specimens at -20 °C | |
| Hard Drive | Dell | Disk space: 500 GB per volume | |
| Image bnarization and segmentation software | Skyscan-Bruker, Kontich, Belgium | CT analyzer | Image processing software |
| Image elastic segmentation | The University of Sheffield | Bone DVC | https://bonedvc.insigneo.org/dvc/ |
| Image processing and automation software | The MathWork Inc. | Matlab | Image processing software |
| Image registration software | Skyscan-Bruker, Kontich, Belgium | DataViewer | Image processing software |
| Image segmentation and FE modelling software | Simpleware, Exeter, UK | Scan IP | Bone egmentation software |
| Image stiching script | Australian syncrotron, Clayton, VIC, AU | The script is available at IMBL | |
| Image visualization | Kitware, Clifton Park, NY, USA | Paraview | Image visualization |
| Image visualization | Australian National University | Dristhi | Image visualization: doi:10.1117/12.935640 |
| Imaging and Medical beamline | Australian syncrotron, Clayton, VIC, AU | Large object micro-CT beamline at the Australian Synchrotron | |
| Laptop | Dell Inc., USA | ||
| Low-friction x-y table | THK Co., Tokyo, Japan | ||
| NI signal acquisition software | National Instruments, Austin, TX | NI-DAQmx | |
| Phosphate-buffered saline solution | Custom-made | Maintain the bone moisture throughout the experiment | |
| Plastic bag | N/A | Maintain the bone moisture throughout the experiment | |
| Rail | SKF Inc., Lansdale, PA, USA | ||
| Screw-jack mechanism | Benzlers, Örebro, Sweden | Serie BD (warm gear unit) | stroke: 150 mm, maximal load: 10,000 N, gear ratio: 27:1, a displacement per revolution: 0.148 mm |
| Single pco.edge sensor, lens coupled scintillator | Australian syncrotron, Clayton, VIC, AU | Detector Ruby FOV: 141 x 119 mm; 2560 x 2160 px; 55 µm/px; 50 fps | |
| Six axis load cell | ME-Meßsysteme GmbH, Hennigsdorf, GE | K6D6 | Maximal measurement error: 0.005%; maximal force: 10000 N; maximal torque: 500 Nm |
| Strain amplifier | ME-Meßsysteme GmbH, Hennigsdorf, GE | GSV-1A8USB K6D/M16 |
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