Summary

人髋关节微观结构失效机制的成像

Published: September 29, 2023
doi:

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

该协议是用从遗体捐赠计划中收到的 12 个股骨标本开发和测试的。将标本新鲜获得并储存在-20°C的弗林德斯大学生物力学和植入物实验室(澳大利亚南澳大利亚州Tonsley)。在整个实验过程中保持骨骼水分。捐赠者是白人妇女(66-80岁)。从弗林德斯大学社会和行为研究伦理委员会(SBREC)获得伦理许可(项目#6380)。 1. 规划特定于试样的载荷阶跃增量 使?…

Representative Results

这些图像显示了整个股骨近端、压力窝、牙科水泥、铝杯和包裹组织。随着骨折前和骨折后负荷的增加,可以看到骨微结构逐渐变形(图 4)。 图 4:连接到笔记本电脑的 压缩阶段。 (A) 压缩阶段,(B…

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?…

Divulgazioni

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

Riferimenti

  1. Martelli, S., Perilli, E. Time-elapsed synchrotron-light microstructural imaging of femoral neck fracture. Journal of the Mechanical Behavior of Biomedical Materials. 84, 265-272 (2018).
  2. Martelli, S., Giorgi, M., Dall’ Ara, E., Perilli, E. Damage tolerance and toughness of elderly human femora. Acta Biomaterialia. 123, 167-177 (2021).
  3. Perilli, E., et al. Dependence of mechanical compressive strength on local variations in microarchitecture in cancellous bone of proximal human femur. Journal of Biomechanics. 41 (2), 438-446 (2008).
  4. Thurner, P. J., et al. Time-lapsed investigation of three-dimensional failure and damage accumulation in trabecular bone using synchrotron light. Bone. 39 (2), 289-299 (2006).
  5. Jackman, T. M. Quantitative, 3D visualization of the initiation and progression of vertebral fractures under compression and anterior flexion. Journal of Bone and Mineral Research. 31 (4), 777-788 (2016).
  6. Mayhew, P. M., et al. Relation between age, femoral neck cortical stability, and hip fracture risk. Lancet. 366 (9480), 129-135 (2005).
  7. Nazarian, A., Stauber, M., Zurakowski, D., Snyder, B. D., Müller, R. The interaction of microstructure and volume fraction in predicting failure in cancellous bone. Bone. 39 (6), 1196-1202 (2006).
  8. Schileo, E., et al. To what extent can linear finite element models of human femora predict failure under stance and fall loading configurations. Journal of Biomechanics. 47 (14), 3531-3538 (2014).
  9. Schileo, E., et al. An accurate estimation of bone density improves the accuracy of subject-specific finite element models. Journal of Biomechanics. 41 (11), 2483-2491 (2008).
  10. Dall’ara, E., et al. A nonlinear QCT-based finite element model validation study for the human femur tested in two configurations in vitro. Bone. 52 (1), 27-38 (2013).
  11. Perilli, E., Parkinson, I. H., Reynolds, K. J. Micro-CT examination of human bone: from biopsies towards the entire organ. Annali dell’Istituto Superiore di Sanità. 48 (1), 75-82 (2012).
  12. Wearne, L. S., Rapagna, S., Taylor, M., Perilli, E. Micro-CT scan optimisation for mechanical loading of tibia with titanium tibial tray: A digital volume correlation zero strain error analysis. Journal of the Mechanical Behavior of Biomedical Materials. 134, 105336 (2022).
  13. Bennett, K. J., et al. Ex vivo assessment of surgically repaired tibial plateau fracture displacement under axial load using large-volume micro-CT. Journal of Biomechanics. 144, 111275 (2022).
  14. Falcinelli, C., et al. Multiple loading conditions analysis can improve the association between finite element bone strength estimates and proximal femur fractures: A preliminary study in elderly women. Bone. 67, 71-80 (2014).
  15. Orthopedic Image Segmentation. Synopsys Available from: https://www.synopsys.com/simpleware/news-and-events/ortho-medical-image-segmentation.html (2020)

Play Video

Citazione di questo articolo
Martelli, S., Perilli, E. Imaging of the Microstructural Failure Mechanism in the Human Hip. J. Vis. Exp. (199), e64947, doi:10.3791/64947 (2023).

View Video