Name: imaging of the microstructural failure mechanism in the human hip
Uploaded: 2023-09-29T13:50:00
Description: Watch this Scientific Journal Video about Imaging of the Microstructural Failure Mechanism in the Human Hip at JoVE.com

Funding from the Australian Research Council (FT180100338; IC190100020) is gratefully acknowledged.

The protocol was developed and tested with 12 femur specimens received from a body donation program. The specimens were obtained fresh and stored at &#8722;20 &#176;C at the Biomechanics and Implants Laboratory of Flinders University (Tonsley, South Australia, Australia). Bone moisture was maintained throughout the experiment. The donors were Caucasian women (66-80 years of age). Ethics clearance was obtained from the Social and Behavioural Research Ethics Committee (SBREC) of Flinders University (Project # 6380).
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<ol>
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D., M&#252;ller, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+interaction+of+microstructure+and+volume+fraction+in+predicting+failure+in+cancellous+bone.">The interaction of microstructure and volume fraction in predicting failure in cancellous bone.</a> Bone. 39 (6), 1196-1202 (2006).</li><li>Schileo, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=To+what+extent+can+linear+finite+element+models+of+human+femora+predict+failure+under+stance+and+fall+loading+configurations.">To what extent can linear finite element models of human femora predict failure under stance and fall loading configurations.</a> Journal of Biomechanics. 47 (14), 3531-3538 (2014).</li><li>Schileo, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+accurate+estimation+of+bone+density+improves+the+accuracy+of+subject-specific+finite+element+models.">An accurate estimation of bone density improves the accuracy of subject-specific finite element models.</a> Journal of Biomechanics. 41 (11), 2483-2491 (2008).</li><li>Dall'ara, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+nonlinear+QCT-based+finite+element+model+validation+study+for+the+human+femur+tested+in+two+configurations+in+vitro.">A nonlinear QCT-based finite element model validation study for the human femur tested in two configurations in vitro.</a> Bone. 52 (1), 27-38 (2013).</li><li>Perilli, E., Parkinson, I. 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The present protocol allows for studying the time-elapsed micromechanics of hip fractures in three dimensions ex vivo. A radiotransparent (aluminium) compressive stage&#160;capable of applying a progressive deformation to the proximal half of the human femur and measuring the reaction force has been custom-designed, manufactured, and tested. A large-volume micro-CT scanner is employed in this protocol to provide a temporal sequence of image volumes displaying the entire proximal femur with progressive loading at...

Fractures of the femoral neck are a major burden to the aging population. Micro-computed tomography (micro-CT) imaging and concomitant mechanical testing&#160;allow for observing the bone microstructure and studying its relationship to bone strength, its age-related changes, and displacements under load1,2. However, until recently, micro-CT studies of bone under load were limited to excised bone cores3, small animals4, and human spine units5. The present protocol can quantify the displacement of the microstructure of the entire proximal human femur under load and after a fracture.
Several studies have been conducted to investigate the failure of the human femur, and at times, these have reached contrasting conclusions. For example, the age-related thinning of the cortical and trabecular structures is thought to determine the age-related susceptibility to fracture by causing elastic instability of the bone6,7, which is in apparent contrast with the high coefficient of determination of cortical strain and femoral strength predictions assuming no elastic instability (R2 = 0.80-0.97)8,9. Nevertheless, such studies have systematically underestimated the femoral strength (by 21%-29%), thus bringing into question the brittle and quasi-brittle bone responses implemented in the models8,10. One possible explanation for these apparently contrasting findings may reside in a different fracture behavior of entire bones compared to isolated bone cores. Therefore, observing the deformation and fracture responses of the bone microstructure in entire proximal femurs may advance knowledge of hip fracture mechanics and related applications.
Current methods for imaging entire human bones with micrometric resolution are limited. The gantry and the detector size must provide a suitable working volume to host the human proximal femur (approximately 13 cm x 10 cm, width x length) and possibly a pixel size in the order of 0.02-0.03 mm to ensure that relevant micro-architectural features can be captured11. These specifications can currently be met by some synchrotron facilities1 and some commercially available large-volume micro-CT scanners12,13. The compressive stage has to be radio-transparent in order to minimize X-ray attenuation while generating a force sufficient for causing a fracture to the human femur (e.g., between 0.9 kN and 14.3 kN for elderly white women)14. This large fracture load variation complicates the planning of the number of load steps to fracture, the overall experiment time, and the corresponding amount of data produced. To address this problem, the fracture load and location can be estimated via finite-element modeling by using the bone density distribution of the specimen from clinical computed tomography (CT) images1,2. Finally, after the experiment, the large volume of data generated needs to be processed for studying the failure mechanisms and energy dissipation capacity in the entire human femur.
Here, we describe a protocol for obtaining a sequence of three-dimensional microstructural images of the entire proximal femur under progressively increasing deformation, which causes clinically relevant fractures of the femoral neck2. The protocol includes planning the stepwise increment&#160;of the specimen compression, loading via a custom radio-transparent compressive stage, imaging via a large-volume micro-CT scanner, and processing the images and the load profiles.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Absorbent tissue</td>
			<td>N/A</td>
			<td></td>
			<td>Maintain the bone moisture throughout the experiment</td>
		</tr>
		<tr>
			<td>Alignment rig</td>
			<td>Custom-made</td>
			<td></td>
			<td>Rig for positioning the specimen in the potting cup</td>
		</tr>
		<tr>
			<td>Aluminium potting cup</td>
			<td>Custom-made</td>
			<td></td>
			<td>Potting cup</td>
		</tr>
		<tr>
			<td>Bone saw</td>
			<td>N/A</td>
			<td></td>
			<td>Cut the specimen to size</td>
		</tr>
		<tr>
			<td>Calibration phantom QCT Pro</td>
			<td>Mindways Software, Inc., Austin, USA</td>
			<td>CT Calibration 13002</td>
			<td>Calibrate grey levels in the images into equivalent bone mineral (ash) density levels</td>
		</tr>
		<tr>
			<td>Clinical Computed-Tmography scanner</td>
			<td>General Electric Medical Systems Co., Wisconsin, USA</td>
			<td>Optima CT660</td>
			<td>Preliminary imaging for the prediction of the load step to fracture</td>
		</tr>
		<tr>
			<td>Compressive stage</td>
			<td>Custom-made</td>
			<td></td>
			<td>A 10 kg, radiotransparent compressive stage for applying and maintaining throught imaging a prescribed deformation to the specimen.</td>
		</tr>
		<tr>
			<td>Dental cement</td>
			<td>Soesterberg, The Netherlands</td>
			<td>Vertex RS</td>
			<td></td>
		</tr>
		<tr>
			<td>Femur specimen</td>
			<td>Science Care, Phoenix, USA</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Finite-element analysis software</td>
			<td>ANSYS Inc., Canonsburg, USA</td>
			<td>ANSYS Mechanical APDL</td>
			<td>Finite-element software package</td>
		</tr>
		<tr>
			<td>Freezer</td>
			<td>N/A</td>
			<td></td>
			<td>Store specimens at -20 &#176;C</td>
		</tr>
		<tr>
			<td>Hard Drive</td>
			<td>Dell</td>
			<td></td>
			<td>Disk space: 500 GB per volume</td>
		</tr>
		<tr>
			<td>Image bnarization and segmentation software</td>
			<td>Skyscan-Bruker, Kontich, Belgium</td>
			<td>CT analyzer</td>
			<td>Image processing software</td>
		</tr>
		<tr>
			<td>Image elastic segmentation</td>
			<td>The University of Sheffield</td>
			<td>Bone DVC</td>
			<td>https://bonedvc.insigneo.org/dvc/</td>
		</tr>
		<tr>
			<td>Image processing and automation software</td>
			<td>The MathWork Inc.</td>
			<td>Matlab</td>
			<td>Image processing software</td>
		</tr>
		<tr>
			<td>Image registration software</td>
			<td>Skyscan-Bruker, Kontich, Belgium</td>
			<td>DataViewer</td>
			<td>Image processing software</td>
		</tr>
		<tr>
			<td>Image segmentation and FE modelling software</td>
			<td>Simpleware, Exeter, UK</td>
			<td>Scan IP</td>
			<td>Bone egmentation software</td>
		</tr>
		<tr>
			<td>Image stiching script</td>
			<td>Australian syncrotron, Clayton, VIC, AU</td>
			<td></td>
			<td>The script is available at IMBL</td>
		</tr>
		<tr>
			<td>Image visualization</td>
			<td>Kitware, Clifton Park, NY, USA</td>
			<td>Paraview</td>
			<td>Image visualization</td>
		</tr>
		<tr>
			<td>Image visualization</td>
			<td>Australian National University</td>
			<td>Dristhi</td>
			<td>Image visualization: doi:10.1117/12.935640</td>
		</tr>
		<tr>
			<td>Imaging and Medical beamline</td>
			<td>Australian syncrotron, Clayton, VIC, AU</td>
			<td></td>
			<td>Large object micro-CT beamline at the Australian Synchrotron</td>
		</tr>
		<tr>
			<td>Laptop</td>
			<td>Dell Inc., USA</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Low-friction x-y table</td>
			<td>THK Co., Tokyo, Japan</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>NI signal acquisition software</td>
			<td>National Instruments, Austin, TX</td>
			<td>NI-DAQmx</td>
			<td></td>
		</tr>
		<tr>
			<td>Phosphate-buffered saline solution</td>
			<td>Custom-made</td>
			<td></td>
			<td>Maintain the bone moisture throughout the experiment</td>
		</tr>
		<tr>
			<td>Plastic bag</td>
			<td>N/A</td>
			<td></td>
			<td>Maintain the bone moisture throughout the experiment</td>
		</tr>
		<tr>
			<td>Rail</td>
			<td>SKF Inc., Lansdale, PA, USA</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Screw-jack mechanism</td>
			<td>&#160;Benzlers, &#214;rebro, Sweden</td>
			<td>Serie BD (warm gear unit)</td>
			<td>stroke: 150 mm, maximal load: 10,000 N, gear ratio: 27:1, a displacement per revolution: 0.148 mm</td>
		</tr>
		<tr>
			<td>Single pco.edge sensor, lens coupled scintillator</td>
			<td>Australian syncrotron, Clayton, VIC, AU</td>
			<td></td>
			<td>Detector Ruby FOV: 141 x 119 mm; 2560 x 2160 px; 55 &#181;m/px; 50 fps</td>
		</tr>
		<tr>
			<td>Six axis load cell</td>
			<td>ME-Me&#223;systeme GmbH, Hennigsdorf, GE</td>
			<td>K6D6</td>
			<td>Maximal measurement error: 0.005%; maximal force: 10000 N; maximal torque: 500 Nm</td>
		</tr>
		<tr>
			<td>Strain amplifier</td>
			<td>ME-Me&#223;systeme GmbH, Hennigsdorf, GE</td>
			<td>GSV-1A8USB K6D/M16</td>
			<td></td>
		</tr>
	</tbody>
</table>

imaging of the microstructural failure mechanism in the human hip

Imaging the bone microstructure under progressively increasing loads allows for observing the microstructural failure behavior of bone. Here, we describe a protocol for obtaining a sequence of three-dimensional microstructural images of the entire proximal femur under progressively increasing deformation, causing clinically relevant fractures of the femoral neck. The protocol is demonstrated using four femora from female donors aged 66-80 years at the lower end of bone mineral density in the population (T-score range = &#8722;2.09 to &#8722;4.75). A radio-transparent compressive stage was designed for loading the specimens replicating a one-leg stance, while recording the applied load during&#160;micro-computed tomography (micro-CT) imaging. The field of view was 146 mm wide and 132 mm high, and the isotropic pixel size was 0.03 mm. The force increment was based on finite-element predictions of the fracture load. The compressive stage was used to apply the displacement to the specimen and enact the prescribed force increments. Sub-capital fractures due to opening and shear of the femoral neck occurred after four to five load increments. The micro-CT&#160;images and the reaction force measurements were processed to study the bone strain and energy absorption capacity. Instability of the cortex appeared at the early loading steps. The subchondral bone in the femoral head displayed large deformations reaching 16% before&#160;fracture, and a progressive increase in the support capacity up to&#160;fracture. The deformation energy linearly increased with the displacement up to&#160;fracture, while the stiffness decreased to near-zero values immediately before&#160;fracture. Three-fourths of the fracture energy was taken by the specimen during the final 25% force increment. In conclusion, the protocol developed revealed a remarkable energy absorption capacity, or damage tolerance, and a synergic interaction between the cortical and trabecular bone at an advanced donor age.

The images display the entire proximal femur, the pressure socket, the dental cement, the aluminum cup, and the wrapping tissue. The bone micro-architecture can be seen progressively deforming as the load increases before fracture and after fracture (Figure 4).
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/64947/64947fig04.jpg" /> 
Figure 4: The compressive stage con...

Watch this Scientific Journal Video about Imaging of the Microstructural Failure Mechanism in the Human Hip at JoVE.com

Imaging of the Microstructural Failure Mechanism in the Human Hip

The protocol enables the measurement of the deformation of the bone microstructure in the entire proximal human femur and its toughness by combining large-volume micro-CT scanning, a custom-made compressive stage, and advanced image processing tools.

Imaging the bone microstructure under progressively increasing loads allows for observing the microstructural failure behavior of bone. Here, we describe ...

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