Name: method and instrumented fixture for femoral fracture testing in a sideways fall-on-the-hip position
Uploaded: 2017-08-17T12:30:00
Description: Watch this Scientific Journal Video about Method and Instrumented Fixture for Femoral Fracture Testing in a Sideways Fall-on-the-Hip Position at JoVE.com

We would like to thank the Materials and Structural Testing Core Facility and Division of Engineering at Mayo Clinic for technical support. In addition we would like to thank Lawrence J. Berglund, James Bronk, Brant Newman, Jorn op den Buijs, Ph.D., for their help during the study. This study was financially supported by the Grainger Innovation Fund from the Grainger Foundation.

1. Large Fixture Attachment
<ol>
	<li>Remove standard fixtures from the machine.</li>
	<li>Move crosshead apart to accommodate the in-house fixture.</li>
	<li>Place the aluminum block (part No. 1 in Figure 1A) on the machine and securely fasten on the machine using two bolts; the hole in the center accommodates the machine load cell.</li>
	<li>Place the main fixture structure (part No. 2 in Figure 1B) on the aluminum block and securely attach it to the block u...

<ol>
	<li>Bouxsein, M. L., Szulc, P., Munoz, F., Thrall, E., Sornay-Rendu, E., Delmas, P. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Contribution+of+trochanteric+soft+tissues+to+fall+force+estimates,+the+factor+of+risk,+and+prediction+of+hip+fracture+risk.">Contribution of trochanteric soft tissues to fall force estimates, the factor of risk, and prediction of hip fracture risk.</a> J Bone Miner Res. 22, 825-831 (2007).</li><li>Rezaei, A., Dragomir-Daescu, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Femoral+Strength+Changes+Faster+With+Age+Than+BMD+in+Both+Women+and+Men:+A+Biomechanical+Study.">Femoral Strength Changes Faster With Age Than BMD in Both Women and Men: A Biomechanical Study.</a> J Bone Miner Res. 30, 2200-2206 (2015).</li><li>Zani, L., Erani, P., Grassi, L., Taddei, F., Cristofolini, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Strain+distribution+in+the+proximal+Human+femur+during+in+vitro+simulated+sideways+fall.">Strain distribution in the proximal Human femur during in vitro simulated sideways fall.</a> J Biomech. 48, 2130-2143 (2015).</li><li>Dragomir-Daescu, D., 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=Robust+QCT/FEA+models+of+proximal+femur+stiffness+and+fracture+load+during+a+sideways+fall+on+the+hip.">Robust QCT/FEA models of proximal femur stiffness and fracture load during a sideways fall on the hip.</a> Ann Biomed Eng. 39, 742-755 (2011).</li><li>Schileo, E., Balistreri, L., Grassi, L., Cristofolini, L., Taddei, F. <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> J Biomech. 47, 3531-3538 (2014).</li><li>Koivumaki, J. 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=Ct-based+finite+element+models+can+be+used+to+estimate+experimentally+measured+failure+loads+in+the+proximal+femur.">Ct-based finite element models can be used to estimate experimentally measured failure loads in the proximal femur.</a> Bone. 50, 824-829 (2012).</li><li>Pottecher, P., 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=Prediction+of+Hip+Failure+Load:+In+Vitro+Study+of+80+Femurs+Using+Three+Imaging+Methods+and+Finite+Element+Models—The+European+Fracture+Study+(EFFECT).">Prediction of Hip Failure Load: In Vitro Study of 80 Femurs Using Three Imaging Methods and Finite Element Models—The European Fracture Study (EFFECT).</a> Radiology. , 142796 (2016).</li><li>Rivadeneira, F., 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=Femoral+neck+BMD+is+a+strong+predictor+of+hip+fracture+susceptibility+in+elderly+men+and+women+because+it+detects+cortical+bone+instability:+the+Rotterdam+Study.">Femoral neck BMD is a strong predictor of hip fracture susceptibility in elderly men and women because it detects cortical bone instability: the Rotterdam Study.</a> J Bone Miner Res. 22, 1781-1790 (2007).</li><li>de Bakker, P. M., Manske, S. L., Ebacher, V., Oxland, T. R., Cripton, P. A., Guy, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=During+sideways+falls+proximal+femur+fractures+initiate+in+the+superolateral+cortex:+evidence+from+high-speed+video+of+simulated+fractures.">During sideways falls proximal femur fractures initiate in the superolateral cortex: evidence from high-speed video of simulated fractures.</a> J Biomech. 42, 1917-1925 (2009).</li><li>Courtney, A. C., Wachtel, E. F., Myers, E. R., Hayes, W. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Age-related+reductions+in+the+strength+of+the+femur+tested+in+a+fall-loading+configuration.">Age-related reductions in the strength of the femur tested in a fall-loading configuration.</a> J Bone Joint Surg Am. 77, 387-395 (1995).</li><li>Cheng, X. G., 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=Assessment+of+the+strength+of+proximal+femur+in+vitro:+relationship+to+femoral+bone+mineral+density+and+femoral.">Assessment of the strength of proximal femur in vitro: relationship to femoral bone mineral density and femoral.</a> Bone. 20, 213-218 (1997).</li><li>Courtney, A. C., Wachtel, E. F., Myers, E. R., Hayes, W. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+loading+rate+on+strength+of+the+proximal+femur.">Effects of loading rate on strength of the proximal femur.</a> Calcif Tissue Int. 55, 53-58 (1994).</li><li>Keyak, J., Rossi, S., Jones, K., Les, C., Skinner, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prediction+of+fracture+location+in+the+proximal+femur+using+finite+element+models.">Prediction of fracture location in the proximal femur using finite element models.</a> Medical engineering &amp; physics. 23, 657-664 (2001).</li><li>Nishiyama, K. K., Gilchrist, S., Guy, P., Cripton, P., Boyd, S. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Proximal+femur+bone+strength+estimated+by+a+computationally+fast+finite+element+analysis+in+a+sideways+fall+configuration.">Proximal femur bone strength estimated by a computationally fast finite element analysis in a sideways fall configuration.</a> J Biomech. 46, 1231-1236 (2013).</li><li>Langton, C. M., Njeh, C. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The physical measurement of bone. , (2016).</li><li>Ariza, O., 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=Comparison+of+explicit+finite+element+and+mechanical+simulation+of+the+proximal+femur+during+dynamic+drop-tower+testing.">Comparison of explicit finite element and mechanical simulation of the proximal femur during dynamic drop-tower testing.</a> J Biomech. 48, 224-232 (2015).</li></ol>

We proposed a protocol to fracture test proximal cadaveric femora in a fall on the hip configuration with which we have successfully tested about 200 samples. The protocol includes several in-house designed fixtures for femoral strength testing under different loading conditions. The fixture allows for testing of both right and left femora at different testing speeds and bone orientations. After mounting the fixture and the measuring instruments, a fiberglass femur is tested to fracture to assure that all the hardware an...

Development of novel methods for femoral fracture risk assessment and fracture prevention for a fall on the hip require a comprehensive understanding of the biomechanical processes involved during fracture. Cadaveric proximal femur strength testing has proven to be effective in determining the relation between femoral strength and factors affecting the structural capacity of the femur providing important insights in this process1,2,3. Experimentally measured femoral strength is also used for validation of Quantitative Computed Tomography-based Finite Element Analysis (QCT/FEA) which enables a non-invasive estimate of fracture strength4,5,6,7.
To date, there is no accepted standard procedure to test whole femoral specimens to fracture. To isolate clinically-measureable variables (such as bone mineral density and geometry) and their influence on femoral strength, it is imperative for experimental testing to be carried out in a controlled and repeatable manner. Cadaveric femora have irregular shapes and range in sizes8 and can be obtained from either male or female cadavers of different ages, making it impossible to test using built-in fixtures of standard testing machines. In a sideways fall on the hip event, the greater trochanter undergoes compressive loading, while the proximal femur may experience complex loading including compression, tension, bending moment, and torsion. Testing such loading scenarios adds complexity to the experimental design. Therefore, a fixture, as one important component of the testing protocol, must be specifically designed, fabricated, and installed to accommodate femoral samples of different shapes and sizes, and different testing speeds. This fixture must also hold the specimens for testing in a range of desired orientations to simulate possible impact loads from a fall on the hip. To meet such a variety of conditions, the fixture needs to have multiple stationary and moving components connected in a manner to minimize play in the system and to obtain a smooth load-displacement response.
Reliable data acquisition is also critical during testing. The experimental design must incorporate the necessary load cells, displacement transducers, signal amplifiers and conditioners to accurately measure forces and moments at all supports. Additionally, high speed videos of both the anterior and posterior views of the femur obtained synchronously with the acquisition of forces are necessary to help understand the sequence of events leading to fracture, characterize fracture types, and precisely define femoral strength4,9.
While there are valuable experimental studies in the literature on whole femur testing, published protocols either lack details on how the testing was performed or are very different from one study to another to truly make them reproducible10,11. The goal of the current work was to introduce a protocol for mechanical testing of femoral samples that can be used as the starting point for an effort to standardize bone tissue testing which can be repeatable and reproducible. To this end, we designed and fabricated a testing fixture which was used to test about 200 cadaveric femora. The testing fixture included a bottom fixture and a crosshead fixture. The bottom fixture (Figure 1A-E) holds the femur at a desired orientation during testing and includes a trochanter load cell and a 6-channel load cell connected to the femoral shaft. It also accommodates three independent translations to allow for positioning of the bone for fracture testing. A rotation point is added to mimic the knee joint. The major parts of the bottom fixture were made up of thick pieces of stainless steel and aluminum to make a very stiff fixture. A load cell is attached to the bottom fixture to measure compressive forces on the greater trochanter during testing. The crosshead fixture (Figure 2A-2E) includes two aluminum base plates and two very stiff slide ball bearings (attached together by an aluminum plate), to account for the movement of the femoral head during testing and also to accommodate for right and left femora. A load cell included in the crosshead fixture measures compressive forces. An aluminum cup attached to the load cell is used to apply the compressive loads to the femoral head. Our method was used for left and right femora of both sexes, with various sizes, neck-shaft angles, bone mineral density, and loading conditions mimicking a sideways fall on the hip. The testing speeds in our experiments were set at 5, 100, and 700 mm/s, but they can be set to any value available on the testing machine. The designed fixture had two main components, one connected to the crosshead of the testing machine and the other connected to the testing frame. Both parts were instrumented with load cells sufficient to measure force and moment boundary conditions at all supports. Additionally, two high-speed video cameras were used to record the fracture events during testing. After fracture, a set of X-rays and Computed Tomography (CT) scans were obtained for post experimental fracture analyses. Results obtained from these experiments including fracture strength and energy are currently used for additional research in diagnostic tools to eventually improve the assessment of proximal fracture strength in osteoporotic patients.

<table>
	<tbody>
		<tr>
			<td>CT scanner</td>
			<td>Siemens</td>
			<td>Somatom Definition scanner (Siemens, Malvern, PA)</td>
			<td>CT scanning equipment</td>
		</tr>
		<tr>
			<td>Quantitative CT Phantom</td>
			<td>Midways Inc, San Francisco, CA</td>
			<td>Model 3 CT calibration Phantom</td>
			<td>Used for obtaining BMD values from Hounsfield units in the CT image</td>
		</tr>
		<tr>
			<td>Hygenic Orthodontic Resin (PMMA)</td>
			<td>Patterson Dental Supply</td>
			<td>H02252</td>
			<td>Controlled substance and can be purchased with proper approval</td>
		</tr>
		<tr>
			<td>Freezer</td>
			<td>Kenmore</td>
			<td>N/A</td>
			<td>This is a -20oC storage for bones</td>
		</tr>
		<tr>
			<td>X-ray scanner</td>
			<td>General Electric</td>
			<td>46-270615P1</td>
			<td>X-ray imaging equipment.</td>
		</tr>
		<tr>
			<td>X-ray films</td>
			<td>Kodak</td>
			<td>N/A</td>
			<td>Used to display x-ray images</td>
		</tr>
		<tr>
			<td>X-ray developer</td>
			<td>Kodak X-Omatic</td>
			<td>M35A X-OMAT</td>
			<td>Used for developing X-ray images</td>
		</tr>
		<tr>
			<td>X-ray Cassette</td>
			<td>Kodak X-Omatic</td>
			<td>N/A</td>
			<td>Used for holding x-ray films</td>
		</tr>
		<tr>
			<td>Physiologic Saline (0.9% Sodium Chloride)</td>
			<td>Baxter</td>
			<td>NDC 0338-0048-04</td>
			<td>Used for keeping samples hydrated</td>
		</tr>
		<tr>
			<td>Scalpels and scrapers</td>
			<td>Bard-Parker</td>
			<td>N/A</td>
			<td>Used to clean the bone from soft tissue</td>
		</tr>
		<tr>
			<td>Fume Hood</td>
			<td>Hamilton</td>
			<td>70532</td>
			<td>Used for ventilation when preparing PMMA for potting of specimens</td>
		</tr>
		<tr>
			<td>Single axis load cell</td>
			<td>Transducer Techniques, Temecula, CA, USA</td>
			<td>LPU-3K; S/N 219627</td>
			<td>Capacity 3000 LBS</td>
		</tr>
		<tr>
			<td>Six channel load cell</td>
			<td>JR3,Woodland, CA</td>
			<td>45E15A4</td>
			<td>Mechanical load rating 1000N</td>
		</tr>
		<tr>
			<td>Linear potentiometer</td>
			<td>Novotechnik, Southborough, MA, USA</td>
			<td></td>
			<td>Used to acquire linear displacements during testing</td>
		</tr>
		<tr>
			<td>Slide ball bearing</td>
			<td>Schneeberger</td>
			<td>Type NK</td>
			<td>Part of the testing fixture</td>
		</tr>
		<tr>
			<td>Mechanical testing machine</td>
			<td>MTS, Minneapolis, MN</td>
			<td>858 Mini Bionix II</td>
			<td>Used for compression of femur</td>
		</tr>
		<tr>
			<td>Lighting unit</td>
			<td>ARRI</td>
			<td></td>
			<td>Needed for high speed video recordings</td>
		</tr>
		<tr>
			<td>high-speed video camera</td>
			<td>Photron Inc., San Diego, CA, USA</td>
			<td>Photron Fastcam APX-RS</td>
			<td>Used to capture the high speed video recordings of the fracture events</td>
		</tr>
		<tr>
			<td>Photron FASTCAM Viewer</td>
			<td>Photron Inc., San Diego, CA, USA</td>
			<td>Ver.3392(x64)</td>
			<td>Used to view the high speed video recordings</td>
		</tr>
		<tr>
			<td>Camera lens</td>
			<td>Zeiss</td>
			<td>Zeiss Planar L4/50 ZF Lens</td>
			<td>Needed to high image resolution</td>
		</tr>
		<tr>
			<td>Signal conditioner board (DAQ)</td>
			<td>National Instruments</td>
			<td></td>
			<td>Input/output signal connector</td>
		</tr>
		<tr>
			<td>Signal Express</td>
			<td>National Instruments</td>
			<td>N/A</td>
			<td>Data acquisition software</td>
		</tr>
		<tr>
			<td>Laptop Computer</td>
			<td>Dell</td>
			<td>N/A</td>
			<td>Used to monitor and acquire all signals from the testing procedure</td>
		</tr>
	</tbody>
</table>

method and instrumented fixture for femoral fracture testing in a sideways fall-on-the-hip position

Mechanical testing of femora brings valuable insights into understanding the contribution of clinically-measureable variables such as bone mineral density distribution and geometry on the femoral mechanical properties. Currently, there is no standard protocol for mechanical testing of such geometrically complex bones to measure strength, and stiffness. To address this gap we have developed a protocol to test cadaveric femora to fracture and to measure their biomechanical parameters. This protocol describes a set of adaptable fixtures to accommodate the various load magnitudes and directions accounting for possible bone orientations in a fall on the hip configuration, test speed, bone size, and left leg-right leg variations. The femora were prepared for testing by cleaning, cutting, scanning, and potting the distal end and greater trochanter contact surfaces in poly(methyl methacrylate) (PMMA) as presented in a different protocol. The prepared specimens were placed in the testing fixture in a position mimicking a sideways fall on the hip and loaded to fracture. During testing, two load cells measured vertical forces applied to the femoral head and greater trochanter, a six-axis load cell measured forces and moments at the distal femoral shaft, and a displacement sensor measured differential displacement between the femoral head and trochanter contact supports. High speed video cameras were used to synchronously record the sequence of fracture events during testing. The reduction of this data allowed us to characterize the strength, stiffness, and fracture energy for nearly 200 osteoporotic, osteopenic, and normal cadaveric femora for further development of engineering-based diagnostic tools for osteoporosis research.

In-house fixtures are mounted after the standard fixtures are removed from the testing machine. First, the bottom heavy fixture is mounted and secured (Figure 1). This includes an extended arm to hold the 6-channel load cell which also enables the femoral shaft to be aligned at a desired adduction angle. Next, the crosshead fixture including two frictionless slide bearings is mounted to accommodate the application of load and femoral head movement during frac...

Watch this Scientific Journal Video about Method and Instrumented Fixture for Femoral Fracture Testing in a Sideways Fall-on-the-Hip Position at JoVE.com

Method and Instrumented Fixture for Femoral Fracture Testing in a Sideways Fall-on-the-Hip Position

In this manuscript, we present a protocol to fracture test cadaveric proximal femora in a sideways fall on the hip configuration using instrumented fixtures mounted on a standard servo hydraulic frame. Nine digitized signals comprising forces, moments, and displacement along with two high speed video streams are acquired during testing.

Mechanical testing of femora brings valuable insights into understanding the contribution of clinically-measureable variables such as bone mineral density ...

The overall goal of this experimental cadaveric femoral fracture testing protocol is to obtain consistent reproducible fracture strength measurements. This method can help answer key questions in osteoporosis research, by measuring the differences between osteoporotic and normal femoral strength. The main advantage of this technique is that, the testing apparatus mimics a physiological site based fall on the hip.For attachment of the large fixture, first, securely fasten the aluminum block onto the machine. Next, use bolts to secure the main fixture structure onto the aluminum block and support the fixture with the placement of a four ton jack, under the part of fixture that does not rest on the aluminum block. Then use more bolts to secure a six channel load cell fixture onto the main fixture.For attachment of the crosshead fixture, attach the first base plate with the machine crosshead set to absolute zero and the curved edges of the base plate, facing the front of the testing machine. Use one pivoting screw to attach the second base plate. Then, attach the assembly of the two slide bearings, to the second base plate.Rotate the second base plate in a such a way, that the second set of screws can be accessed from the top of the first base plate. Then set the machine crosshead to a relative position of 65 degrees, to allow manual rotation of the slides, orthogonal to the six channel load cell. Once the instrumented fixture has been assembled on the standard server hydraulic machine, attach a high speed camera and lighting equipment to tripods.Position the camera facing the testing machine and connect camera to data acquisition unit. After connecting the data acquisition system, manually push the load cell and observe the data signal traces in the view panel of the DAQ software. To confirm the proper connection and synchronization of the trigger signal, tricanteric load cell, head load cell, linear potentiometer and six channel load cell.Calibrate the linear potentiometer, secure the linear potentiometer fixture to the crosshead and attach the potentiometer to the fixture. Tighten the screws to lock the potentiometer body and plug the connector into the DAQ unit. Next, manually move the actuator 25 millimeters on a load frame, so that the potentiometer position translate from the maximum compression to the maximum extension and record the displacements and the corresponding voltage for at least three data points.Plot the displacement versus the voltage and fit a linear function to the data. Then input the slope of the linear equation as the calibration factor into the scanning parameter box of the DAQ software. To prepare the bone for testing, place a clean 24 hour thawed bone in the acrylic scanning fixture and mix 60 grams of poly or PMMA powder, with 30 grams of liquid resin in a disposable cup under a fume hood, until the powder has dissolved.When the PMMA is pourable, align an aluminum cup below the tricanter and decant the PMMA cement to half the height of the cup. Raise the fixture platform to fit the bone into the cup and allow the PMMA to polymerise for 10 to 15 minutes. When the PMMA is clear and hard, move the bone to the test fixture and center the aluminum cup on the plate, attached to the tricanteric load cell.Adjust the six channel load cell linear stages, so that the aluminum cup lightly touches the load cell and remove the pin from the fixture to a lateral rotation of the fixture. Then center and lower the crosshead for contact with the femoral head and image the femur from two sides. After verifying that the servo mechanical load frame is appropriately programmed, click start to initiate the test sequence for fracturing the test femur.After the test is complete, manually retract the actuator. Remove the bone from the fixture and tape the proximal broken end of the bone to the shaft. Then wrap the bone Wet towels and plastic bags and return the bone to 20 degree celsius storage.After fracture, the force recorded at the greater tricanter and the displacement recorded at the femoral head, using the six channel load cell can be plotted. The broken parts of the bone can then be taped together for further fracture type imaging and classification. While attempting this procedure, it's important to remember to verify that all of the data acquisition systems, function properly with fiberglass femurs before testing the cadaveric specimens.After its development, this technique paved the way for researchers in the field of computational biomechanics, to validate quantitative computer tomography based finite element predictions of strength in osteoporotic femurs. After watching this video, you should have a good understanding on how to test cadaveric femurs in a fall on a hip configuration.

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