Department of the Army #W81XWH-08-1-0587, #W81XWH-15-1-0006; Ball State University 2010 ASPiRE grant.

<ol>
	<li>Brukner, P., Bennell, K., Matheson, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Stress fracture. , (1999).</li><li>Zadpoor, A., Nikooyan, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+relationship+between+lower-extremity+stress+fractures+and+the+ground+reaction+force:+A+systematic+review.">The relationship between lower-extremity stress fractures and the ground reaction force: A systematic review.</a> Clin Biomech. 26, 23-28 (2011).</li><li>Matheson, G. O., Clement, D. B., McKenzie, D. C., Taunton, J. E., Lioyd-Smith, D. R., Maclntyre, J. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stress+fractures+in+athletes.+A+study+of+320+cases.">Stress fractures in athletes. A study of 320 cases.</a> Am J Sports Med. 15, 46-58 (1987).</li><li>Bennell, K., Grimston, S., Burr, D., Milgrom, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Risk+factors+for+developing+stress+fractures.">Risk factors for developing stress fractures.</a> Musculoskeletal fatigue and stress fractures. , 15-33 (2001).</li><li>Milgrom, C., Giladi, M., Stein, M., Kashtan, H., Margulies, J. Y., Chisin, R., Stenberg, R., Aharonson, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stress+fractures+in+military+recruits.+A+prospective+study+showing+an+unusually+high+incidence.">Stress fractures in military recruits. A prospective study showing an unusually high incidence.</a> J Bone Joint Surg Br. 67, 732-735 (1985).</li><li>Almeida, S. A., Williams, K. M., Shaffer, R. A., Brodine, 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=Epidemiological+patterns+of+musculoskeletal+injuries+and+physical+training.">Epidemiological patterns of musculoskeletal injuries and physical training.</a> Med Sci Sports Exerc. 31, 1176-1182 (1999).</li><li>Jones, B. H., Knapik, J. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Physical+training+and+exercise-related+injuries,+surveillance,+research+and+injury+prevention+in+military+populations.">Physical training and exercise-related injuries, surveillance, research and injury prevention in military populations.</a> Sports Med. 27, 111-125 (1999).</li><li>Jones, B. H., Thacker, S., Gilchrist, J., Kimsey, C. D., Sosin, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prevention+of+lower+extremity+stress+fractures+in+athletes+and+soldiers:+a+systematic+review.">Prevention of lower extremity stress fractures in athletes and soldiers: a systematic review.</a> Epidemiol Rev. 24, 228-247 (2002).</li><li>Voloshin, A., Wosk, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+in+vivo+study+of+low+back+pain+and+shock+absorption+in+the+human+locomotor+system.">An in vivo study of low back pain and shock absorption in the human locomotor system.</a> J Biomech. 15, 21-27 (1982).</li><li>Burr, D. B., Milgrom, C., Fyhrie, D., Forwood, M., Nyska, M., Finestone, A., Hoshaw, S., Saiag, E., Simkin, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vivo+measurement+of+human+tibial+strains+during+vigorous+activity.">In vivo measurement of human tibial strains during vigorous activity.</a> Bone. 18, 405-410 (1996).</li><li>Ekenman, I., Halvorsen, K., Westblad, P., Fellander-Tsai, L., Rolf, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+reliability+and+validity+of+an+instrumented+staple+system+for+in+vivo+measurement+of+local+bone+deformation.+An+in+vitro+study.">The reliability and validity of an instrumented staple system for in vivo measurement of local bone deformation. An in vitro study.</a> Scand J Med Sci Sports. 8, 172-176 (1998).</li><li>Lanyon, L. E., Hampson, W. G., Goodship, A. E., Shah, J. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bone+deformation+recorded+in+vivo+from+strain+gauges+attached+to+the+human+tibial+shaft.">Bone deformation recorded in vivo from strain gauges attached to the human tibial shaft.</a> Acta Orthop Scand. 46, 256-268 (1975).</li><li>Ekenman, I., Halvorsen, K., Westblad, P., Tsai, L. F., Rolf, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Local+bone+deformation+at+two+predominant+sites+for+stress+fractures+of+the+tibia:+an+in+vivo+study.">Local bone deformation at two predominant sites for stress fractures of the tibia: an in vivo study.</a> Foot Ankle Int. 19, 479-484 (1998).</li><li>Milgrom, C., Finestone, A., Levi, Y., Simkin, A., Ekenman, I., Mendelson, S., Millgram, M., Nyska, M., Benjuya, N., Burr, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Do+high+impact+exercises+produce+higher+tibial+strains+than+running?.">Do high impact exercises produce higher tibial strains than running?.</a> Br J Sports Med. 34, 195-199 (2000).</li><li>Milgrom, C., Finestone, A., Simkin, A., Ekenman, I., Mendelson, S., Millgram, M., Nyska, M., Larsson, E., Burr, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In-vivo+strain+measurements+to+evaluate+the+strengthening+potential+of+exercises+on+the+tibial+bone.">In-vivo strain measurements to evaluate the strengthening potential of exercises on the tibial bone.</a> J Bone Joint Surg Br. 82, 591-594 (2000).</li><li>Al Nazer, R., Rantalainen, T., Heinonen, A., Sievanen, H., Mikkola, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Flexible+multibody+simulation+approach+in+the+analysis+of+tibial+strain+during+walking.">Flexible multibody simulation approach in the analysis of tibial strain during walking.</a> J Biomech. 41, 1036-1043 (2008).</li><li>Al Nazer, R., Klodowski, A., Rantalainen, T., Heinonen, A., Sievanen, H., Mikkola, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+full+body+musculoskeletal+model+based+on+flexible+multibody+simulation+approach+utilised+in+bone+strain+analysis+during+human+locomotion.">A full body musculoskeletal model based on flexible multibody simulation approach utilised in bone strain analysis during human locomotion.</a> Comput Method Biomec. 14, 573-579 (2011).</li><li>Johnson, M. A., Moradi, M. H., Crowe, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> PID control: new identification and design methods. , 543 (2005).</li><li>Craig, R. R., Bampton, M. C. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Coupling+of+substructures+for+dynamics+analysis.">Coupling of substructures for dynamics analysis.</a> American Institute of Aeronautics and Astronautics Journal. 6, 1313-1319 (1968).</li><li>Wasfy, T. M., Noor, A. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Computational+strategies+for+flexible+multibody+systems.">Computational strategies for flexible multibody systems.</a> Appl Mech Rev. 56, 553-613 (2003).</li><li>Kadaba, M. P., Ramakrishnan, H. k., Wootten, M. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurement+of+lower+extremity+kinematics+during+level+walking.">Measurement of lower extremity kinematics during level walking.</a> J Orthop Res. 8, 383-392 (1990).</li><li>Schwartz, M. H., Rozumalski, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+new+method+for+estimating+joint+parameters+from+motion+data.">A new method for estimating joint parameters from motion data.</a> J Biomech. 38, 107-116 (2005).</li><li>Devita, P., Skelly, W. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+landing+stiffness+on+joint+kenetics+and+energetic+in+the+lower+extremity.">Effect of landing stiffness on joint kenetics and energetic in the lower extremity.</a> Med Sci Sports Exerc. 24, 108-115 (1992).</li><li>Dong, X. N., Guo, X. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+dependence+of+transversely+isotropic+elasticity+of+human+femoral+cortical+bone+on+porosity.">The dependence of transversely isotropic elasticity of human femoral cortical bone on porosity.</a> J Biomech. 37, 1281-1287 (2004).</li><li>Schileo, E., Taddei, F., Malandrino, A., Cristofolini, L., Viceconti, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Subject-specific+finite+element+models+can+accurately+predict+strain+levels+in+long+bones.">Subject-specific finite element models can accurately predict strain levels in long bones.</a> J Biomech. 40, 2982-2989 (2007).</li><li>Pattin, C. A., Caler, W. E., Carter, D. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cyclic+mechanical+property+degradation+during+fatigue+loading+of+cortical+bone.">Cyclic mechanical property degradation during fatigue loading of cortical bone.</a> J Biomech. 29, 69-79 (1996).</li><li>Lifemodeler, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Lifemod Manual. , (2010).</li></ol>

The authors declare that they have no competing financial interests.

The purpose of this study was to develop a non-invasive method to determine tibia deformation during high impact activities. Quantifying tibia strain due to impact loading will lead to a better understanding of tibia stress fracture. In this study, a subject-specific musculoskeletal model was developed, and computer simulations were run to duplicate the drop-landing movements performed in a laboratory setting. The effect of drop-landing height on tibial strain was examined. In this study, we observed that as the drop-lan...

Bone stress injuries, such as stress fractures, are severe overuse injuries requiring long periods of recovery and incurring significant medical cost1,2. Stress fractures are common both in athletic and military populations. Among all sports related injuries, stress fractures account for 10% of the total3. In particular, track athletes face a higher injury rate at 20%4. Soldiers also experience a high rate of stress fractures. For instance, a 6% injury rate was reported for the US Army1 and a 31% injury rate was reported in the Israeli Army5. Among all reported stress fractures, tibia stress fracture is the most common one6,7,8.
Sports and physical trainings with a higher risk of tibia stress fracture are normally associated with high ground impacts (e.g., jumping, landing, and cutting). During locomotion, a ground impact force is applied to the body when the foot contacts the ground. This impact force is dissipated by the musculoskeletal system and footwear. The skeletal system serves as a series of levers allowing muscles to apply forces to absorb the ground impact9. When the leg muscles cannot adequately reduce the ground impact, lower-body bones must absorb the residual force. Bone structure will experience deformation during this process. Repetitive absorption of residual impact force may result in microdamages in the bone, which will accumulate and become stress fractures. To date, information related to bone reaction to external ground impact forces is limited. It is important to study how the tibia bone responds to the mechanical load introduced by high impact forces during dynamic motions. Examining tibia bone deformation during high impact activities could lead to a better understanding of the mechanism of tibia stress fracture.
Conventional techniques used to measure bone deformation in vivo rely on instrumented strain gauges10,11,12,13,14,15. Surgical procedures are needed to implant strain gauges on bone surface. Due to the invasive nature, in vivo studies are limited by a small sample of volunteers. In addition, the strain gauge can only monitor a small region of the bone surface. Recently, a non-invasive method utilizing computer simulation to analyze bone strain was introduced16,17. This methodology allows for the ability to combine musculoskeletal modeling and computational simulations to study bone strain during human movement.
A musculoskeletal model is represented by a skeleton and skeletal muscles. The skeleton consists of bone segments, which are rigid or non-deformable bodies. Skeletal muscles are modeled as controllers using the progressive-integral-derivative (PID) algorithm. The three-term PID control uses errors in estimation to improve the output accuracy18. In essence, PID controllers representing muscles try to duplicate body movements by developing necessary forces to produce length changes of the muscles over time. The PID controller uses the error in the length/time curve to modify the force for reproducing the movement. This simulation process creates a feasible solution to coordinate all muscles to work together to move the skeleton and produce the body movement.
One or more segments in the skeleton of the musculoskeletal model can be modeled as flexible bodies to allow measurement of deformation. For instance, the tibia bone can be broken down into a finite number of elements, which consists of thousands of elements and nodes. The effect of mechanical loading on the flexible tibia can be examined through finite element (FE) analysis. The FE analysis calculates the loading response of individual elements over time. As the number of bone elements and nodes increase, the computation time of the FE analysis will significantly increase.
To reduce computational cost with accurate evaluation of flexible bodies&#39; deformation, modal FE analysis has been developed and used within the automotive and aerospace industry19,20. Instead of analyzing individual FE elements&#39; responses to mechanical load in the time domain, this procedure assesses an object&#39;s mechanical responses based on different vibrational frequencies in the frequency domain. This method results in a significant reduction in computation time while providing accurate measurement of deformation20. Although modal FE analysis has been widely used to study mechanical fatigue in automotive and aerospace areas, the application of this method has been very limited in human movement science. Al Nazer et al., used a modal FE analysis to examine tibial deformation during human gait and reported encouraging results16,17. However, their method was greatly affected by only using limited kinematic data from an experiment to drive the computer simulations; There were no real ground impact forces used to assist the simulations. This approach may be reasonable for studying low impact slow motions such as walking, but it is not a feasible solution to study high ground impact movements. Thus, in order to examine lower-body bone reactions during dynamic high impact activities, it is essential to develop an innovative approach to address the limitations associated with the previously reported method. Specifically, a method utilizing accurate experimental kinematic data and real ground impact forces must be developed. Therefore, the goal of this study was to develop a subject-specific musculoskeletal model to perform multibody dynamic simulations with modal FE analysis to examine tibial strain during high impact activities. A dynamic high impact movement represented by drop-landings from different heights was selected to test the method.

<table><tbody><tr><td>CT Scanner</td><td>GE Medical System</td><td>N/A</td><td>Light Speed VCT. For performing tibia CT scan.</td></tr><tr><td>Motion Capture System</td><td>Vicon Inc</td><td>N/A</td><td>Vicon FX40 high speed cameras. For performing 3D motion capture.</td></tr><tr><td>Force plates</td><td>AMTI Inc</td><td>N/A</td><td>Collecting 3D ground reaction forces</td></tr><tr><td>Vicon Nexus</td><td>Vicon Inc</td><td>N/A</td><td>Motion capture software program. For processing visual marker trajectory data.</td></tr><tr><td>Visual 3D</td><td>C-Motion Inc</td><td>N/A</td><td>Biomechanics analysis software. For computing 3D kinematics and kinetics of human movements.</td></tr><tr><td>MATLAB</td><td>Mathworks Inc</td><td>N/A</td><td>Computer programming software. For performing raw data filtering, data conversion, and data processing.</td></tr><tr><td>ADAMS 2012</td><td>MSC Software Inc</td><td>N/A</td><td>Multibody dynamic computer simulation program.</td></tr><tr><td>LifeMOD</td><td>Lifemodeler Inc</td><td>N/A</td><td>A software Plug-in in ADAMS. For building human body musculo-skeletal models.</td></tr><tr><td>MIMICS 13</td><td>Materialise Inc</td><td>N/A</td><td>Image processing program. A 3D modeling tool to process imaging data. For creating 3D tibia model from CT scans.</td></tr><tr><td>MARC 2012</td><td>MSC Software Inc</td><td>N/A</td><td>Finite element analysis software. For performing volumn meshing, generating tibia FE model, and running modal FE analysis.</td></tr><tr><td>SPSS 19</td><td>IBM Inc</td><td>N/A</td><td>Statistical analysis software.</td></tr></tbody></table>

subject-specific musculoskeletal model for studying bone strain during dynamic motion

Bone stress injuries are common in sports and military trainings. Repetitive large ground impact forces during training could be the cause. It is essential to determine the effect of high ground impact forces on lower-body bone deformation to better understand the mechanisms of bone stress injuries. Conventional strain gauge measurement has been used to study in vivo tibia deformation. This method is associated with limitations including invasiveness of the procedure, involvement of few human subjects, and limited strain data from small bone surface areas. The current study intends to introduce a novel approach to study tibia bone strain under high impact loading conditions. A subject-specific musculoskeletal model was created to represent a healthy male (19 years, 80 kg, 1,800 mm). A flexible finite element tibia model was created based on a computed tomography (CT) scan of the subject&#39;s right tibia. Laboratory motion capture was performed to obtain kinematics and ground reaction forces of drop-landings from different heights (26, 39, 52 cm). Multibody dynamic computer simulations combined with a modal analysis of the flexible tibia were performed to quantify tibia strain during drop-landings. Calculated tibia strain data were in good agreement with previous in vivo studies. It is evident that this non-invasive approach can be applied to study tibia bone strain during high impact activities for a large cohort, which will lead to a better understanding of injury mechanism of tibia stress fractures.

A healthy Caucasian male (19 years, height 1,800 mm, mass 80 kg) volunteered for the study. Prior to data collection, the subject reviewed and signed the consent form approved by the University Institutional Review Board before participating in the study. The experiment was conducted under the Helsinki Declaration. The experiment was performed based on the following protocol.
In order to verify the accuracy of the forward dynami...

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Subject-specific Musculoskeletal Model for Studying Bone Strain During Dynamic Motion

During landing, lower-body bones experience large mechanical loads and are deformed. It is essential to measure bone deformation to better understand the mechanisms of bone stress injuries associated with impacts. A novel approach integrating subject-specific musculoskeletal modeling and finite element analysis is used to measure tibial strain during dynamic movements.

Bone stress injuries are common in sports and military trainings. Repetitive large ground impact forces during training could be the cause. It is ...

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9.6K Views.  Ball State University. During landing, lower-body bones experience large mechanical loads and are deformed. It is essential to measure bone deformation to better understand the mechanisms of bone stress injuries associated with impacts. A novel approach integrating subject-specific musculoskeletal modeling and finite element analysis is used to measure tibial strain during dynamic movements.

Video: Subject-specific Musculoskeletal Model for Studying Bone Strain During Dynamic Motion

A Coupled Experiment-finite Element Modeling Methodology for Assessing High Strain Rate Mechanical Response of Soft Biomaterials

This study offers a combined experimental and finite element (FE) simulation approach for examining the mechanical behavior of soft biomaterials (e.g. brain, liver, tendon, fat, etc.) when exposed to high strain rates. This study utilized a Split-Hopkinson Pressure Bar (SHPB) to generate strain rates of 100-1,500 sec-1. The SHPB employed a striker bar consisting of a viscoelastic material (polycarbonate). A sample of the biomaterial was obtained shortly postmortem and prepared for SHPB testing. The specimen was interposed between the incident and transmitted bars, and the pneumatic components of the SHPB were activated to drive the striker bar toward the incident bar. The resulting impact generated a compressive stress wave (i.e. incident wave) that traveled through the incident bar. When the compressive stress wave reached the end of the incident bar, a portion continued forward through the sample and transmitted bar (i.e. transmitted wave) while another portion reversed through the incident bar as a tensile wave (i.e. reflected wave). These waves were measured using strain gages mounted on the incident and transmitted bars. The true stress-strain behavior of the sample was determined from equations based on wave propagation and dynamic force equilibrium. The experimental stress-strain response was three dimensional in nature because the specimen bulged. As such, the hydrostatic stress (first invariant) was used to generate the stress-strain response. In order to extract the uniaxial (one-dimensional) mechanical response of the tissue, an iterative coupled optimization was performed using experimental results and Finite Element Analysis (FEA), which contained an Internal State Variable (ISV) material model used for the tissue. The ISV material model used in the FE simulations of the experimental setup was iteratively calibrated (i.e. optimized) to the experimental data such that the experiment and FEA strain gage values and first invariant of stresses were in good agreement.

The current study prescribes a coupled experiment-finite element simulation methodology to obtain the uniaxial dynamic mechanical response of soft biomaterials (brain, liver, tendon, fat, etc.). The multiaxial experimental results that arose because of specimen bulging obtained from Split-Hopkinson Pressure Bar testing were rendered to a uniaxial true stress-strain behavior when simulated through iterative optimization of the finite element analysis of the biomaterial.

This study offers a combined experimental and finite element (FE) simulation approach for examining the mechanical behavior of soft biomaterials (e.g. ...

A Method to Estimate Cadaveric Femur Cortical Strains During Fracture Testing Using Digital Image Correlation

This protocol describes the method using digital image correlation to estimate cortical strain from high speed video images of the cadaveric femoral surface obtained from mechanical testing. This optical method requires a texture of many contrasting fiduciary marks on a solid white background for accurate tracking of surface deformation as loading is applied to the specimen. Immediately prior to testing, the surface of interest in the camera view is painted with a water-based white primer and allowed to dry for several minutes. Then, a black paint is speckled carefully over the white background with special consideration for the even size and shape of the droplets. Illumination is carefully designed and set such that there is optimal contrast of these marks while minimizing reflections through the use of filters. Images were obtained through high speed video capture at up to 12,000 frames/s. The key images prior to and including the fracture event are extracted and deformations are estimated between successive frames in carefully sized interrogation windows over a specified region of interest. These deformations are then used to compute surface strain temporally during the fracture test. The strain data is very useful for identifying fracture initiation within the femur, and for eventual validation of proximal femur fracture strength models derived from Quantitative Computed Tomography-based Finite Element Analysis (QCT/FEA).

In this protocol, the femur surface strains are estimated during fracture testing using the digital image correlation technique. The novelty of the method involves application of a high-contrast stochastic speckle pattern on the femur surface, carefully specified illumination, high speed video capture, and digital image correlation analysis for strain calculations.

This protocol describes the method using digital image correlation to estimate cortical strain from high speed video images of the cadaveric femoral ...

Quantification of Strain in a Porcine Model of Skin Expansion Using Multi-View Stereo and Isogeometric Kinematics

Tissue expansion is a popular technique in plastic and reconstructive surgery that grows skin in vivo for correction of large defects such as burns and giant congenital nevi. Despite its widespread use, planning and executing an expansion protocol is challenging due to the difficulty in measuring the deformation imposed at each inflation step and over the length of the procedure. Quantifying the deformation fields is crucial, as the distribution of stretch over time determines the rate and amount of skin grown at the end of the treatment. In this manuscript, we present a method to study tissue expansion in order to gain quantitative knowledge of the deformations induced during an expansion process. This experimental protocol incorporates multi-view stereo and isogeometric kinematic analysis in a porcine model of tissue expansion. Multi-view stereo allows three-dimensional geometric reconstruction from uncalibrated sequences of images. The isogeometric kinematic analysis uses splines to describe the regional deformations between smooth surfaces with few mesh points. Our protocol has the potential to bridge the gap between basic scientific inquiry regarding the mechanics of skin expansion and the clinical setting. Eventually, we expect that the knowledge gained with our methodology will enable treatment planning using computational simulations of skin deformation in a personalized manner.

This protocol uses multi-view stereo to generate three-dimensional (3D) models out of uncalibrated sequences of photographs, making it affordable and adjustable to a surgical setting. Strain maps between the 3D models are quantified with spline-based isogeometric kinematics, which facilitate representation of smooth surfaces over coarse meshes sharing the same parameterization.

Tissue expansion is a popular technique in plastic and reconstructive surgery that grows skin in vivo for correction of large defects such as burns and ...

Biplanar Videoradiography Dataset for Model-based Pose Estimation Development and New User Training

Measuring the motion of the small foot bones is critical for understanding pathological loss of function. Biplanar videoradiography is well-suited to measure in vivo bone motion, but challenges arise when estimating the rotation and translation (pose) of each bone. The bone's pose is typically estimated with marker- or model-based methods. Marker-based methods are highly accurate but uncommon in vivo due to their invasiveness. Model-based methods are more common but are currently less accurate as they rely on user input and lab-specific algorithms. This work presents a rare in vivo dataset of the calcaneus, talus, and tibia poses, as measured with marker-based methods during running and hopping. A method is included to train users to improve their initial guesses into model-based pose estimation software, using marker-based visual feedback. New operators were able to estimate bone poses within 2&#176; of rotation and 1 mm of translation of the marker-based pose, similar to an expert user of the model-based software, and representing a substantial improvement over previously reported inter-operator variability. Further, this dataset can be used to validate other model-based pose estimation software. Ultimately, sharing this dataset will improve the speed and accuracy with which users can measure bone poses from biplanar videoradiography.

This work presents an in vivo dataset with bone poses estimated with marker-based methods. A method is included here to train operators in improving their initial estimates for model-based pose estimation and reducing inter-operator variability.

Measuring the motion of the small foot bones is critical for understanding pathological loss of function. Biplanar videoradiography is well-suited to ...

Engineering

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 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 ...

Biplanar Videoradiography to Study the Wrist and Distal Radioulnar Joints

Accurate measurement of skeletal kinematics in vivo is essential for understanding normal joint function, the influence of pathology, disease progression, and the effects of treatments. Measurement systems that use skin surface markers to infer skeletal motion have provided important insight into normal and pathological kinematics, however, accurate arthrokinematics cannot be attained using these systems, especially during dynamic activities. In the past two decades, biplanar videoradiography (BVR) systems have enabled many researchers to directly study the skeletal kinematics of the joints during activities of daily living. To implement BVR systems for the distal upper extremity, videoradiographs of the distal radius and the hand are acquired from two calibrated X-ray sources while a subject performs a designated task. Three-dimensional (3D) rigid-body positions are computed from the videoradiographs via a best-fit registrations of 3D model projections onto&#160;to each BVR view. The 3D models are density-based image volumes of the specific bone derived from independently acquired computed-tomography data. Utilizing graphics processor units and high-performance computing systems, this model-based tracking approach is shown to be fast and accurate in evaluating the wrist and distal radioulnar joint biomechanics. In this study, we first summarized the previous studies that have established the submillimeter and subdegree agreement of BVR with an in vitro&#160;optical motion capture system in evaluating the wrist and distal radioulnar joint kinematics. Furthermore, we used BVR to compute the center of rotation behavior of the wrist joint, to evaluate the articulation pattern of the components of the implant upon one another, and to assess the dynamic change of ulnar variance during pronosupination of the forearm. In the future, carpal bones may be captured in greater detail with the addition of flat panel X-ray detectors, more X-ray sources (i.e., multiplanar videoradiography), or advanced computer vision algorithms.

Biplanar videoradiography (BVR) is an advanced imaging technique for understanding the three-dimensional movement of skeletal bones and implants. Combining density-based image volumes and videoradiographs of the distal upper extremity, BVR is used to study the in vivo motion of the wrist and distal radioulnar joint, as well as joint arthroplasties.

Accurate measurement of skeletal kinematics in vivo is essential for understanding normal joint function, the influence of pathology, disease progression, ...

A Minimally Invasive Model to Analyze Endochondral Fracture Healing in Mice Under Standardized Biomechanical Conditions

Bone healing models are necessary to analyze the complex mechanisms of fracture healing to improve clinical fracture treatment. During the last decade, an increased use of mouse models in orthopedic research was noted, most probably because mouse models offer a large number of genetically-modified strains and special antibodies for the analysis of molecular mechanisms of fracture healing. To control the biomechanical conditions, well-characterized osteosynthesis techniques are mandatory, also in mice. Here, we report on the design and use of a closed bone healing model to stabilize femur fractures in mice. The intramedullary screw, made of medical-grade stainless steel, provides through fracture compression an axial and rotational stability compared to the mostly used simple intramedullary pins, which show a complete lack of axial and rotational stability. The stability achieved by the intramedullary screw allows the analysis of endochondral healing. A large amount of callus tissue, received after stabilization with the screw, offers ideal conditions to harvest tissue for biochemical and molecular analyses. A further advantage of the use of the screw is the fact that the screw can be inserted into the femur with a minimally invasive technique without inducing damage to the soft tissue. In conclusion, the screw is a unique implant that can ideally be used in closed fracture healing models offering standardized biomechanical conditions.

This protocol describes a minimally invasive osteosynthesis technique using an intramedullary screw for standardized stabilization of femur fractures, which can be used to analyze endochondral bone healing in mice.

Bone healing models are necessary to analyze the complex mechanisms of fracture healing to improve clinical fracture treatment. During the last decade, an ...

Medicine

Principles and Protocols of Mechanical Testing for Bone Fracture Susceptibility

Practical Considerations for the Design, Execution, and Interpretation of Studies Involving Whole-Bone Bending Tests of Rodent Bones

Skeletal fragility leading to fracture is an American public health crisis resulting in 1.5 million fractures each year and $18 billion in direct care costs. The ability to understand the mechanisms underlying bone disease and the response to treatment is not only desired, but critical. Mechanical testing of bone serves as a valuable technique for understanding and quantifying a bone&#39;s susceptibility to fracture. While this method appears simple to perform, inappropriate and inaccurate conclusions may be reached if governing assumptions and key steps are disregarded by the user. This has been observed across disciplines as studies continue to be published with misuse of methods and incorrect interpretation of results. This protocol will serve as a primer for the principles associated with mechanical testing along with the application of these techniques-from considerations of sample size through tissue harvesting and storage, to data analysis and interpretation. With this in hand, valuable information regarding a bone&#39;s susceptibility to fracture may be obtained, furthering understanding for both academic research and clinical solutions.

Author Spotlight: Enhancing Accuracy and Reproducibility in Whole Bone Bending Tests 

Mechanical testing of rodent bones is a valuable method for extracting information regarding a bone's susceptibility to fracture. Lacking proper practical understanding, the results may be overinterpreted or lack validity. This protocol will serve as a guide to ensure mechanical tests are performed accurately to provide valid and functional data.

Skeletal fragility leading to fracture is an American public health crisis resulting in 1.5 million fractures each year and $18 billion in direct care ...

Cyclic Mechanical Loading for Inducing Tendinopathy in Rat Achilles Tendon

A Passive Ankle Dorsiflexion Testing System for an In Vivo Model of Overuse-induced Tendinopathy

Tendinopathy is a chronic tendon condition that results in pain and loss of function and is caused by repeated overload of the tendon and limited recovery time. This protocol describes a testing system that cyclically applies mechanical loads via passive dorsiflexion to the rat Achilles tendon. The custom-written code consists of pre- and post-cyclic loading measurements to assess the effects of the loading protocol along with the feedback control-based cyclic fatigue loading regimen. 
We used 25 Sprague-Dawley rats for this study, with 5 rats per group receiving either 500, 1,000, 2,000, 3,600, or 7,200 cycles of fatigue loads. The percentage differences between the pre- and post-cyclic loading measurements of the hysteresis, peak stress, and loading and unloading moduli were calculated. The results demonstrate that the system can induce varying degrees of damage to the Achilles tendon based on the number of loads applied. This system offers an innovative approach to apply quantified and physiological varying degrees of cyclic loads to the Achilles tendon for an in vivo model of fatigue-induced overuse tendon injury.

Author Spotlight: Integrating Mechanical and Biological Analysis in Tendinopathy Research 

This protocol presents a testing system used to induce quantifiable and controlled fatigue injuries in a rat Achilles tendon for an in-vivo model of overuse-induced tendinopathy. The procedure consists of securing the rat's ankle to a joint actuator that performs passive ankle dorsiflexion with a custom-written MATLAB script.

Tendinopathy is a chronic tendon condition that results in pain and loss of function and is caused by repeated overload of the tendon and limited recovery ...

Construction of a Realistic, Whole-Body, Three-Dimensional Equine Skeletal Model using Computed Tomography Data

Therapies based upon whole-body biomechanical assessments are successful for injury prevention and rehabilitation in human athletes. Similar approaches have rarely been used to study equine athletic injury. Degenerative osteoarthritis caused by mechanical stress can originate from chronic postural dysfunction, which, because the primary dysfunction is often distant from the site of tissue injury, is best identified through modeling whole-body biomechanics. To characterize whole-body equine kinematics, a realistic skeletal model of a horse was created from equine computed tomography (CT) data that can be used for functional anatomical and biomechanical modeling. Equine CT data were reconstructed into individual three-dimensional (3D) data sets (i.e., bones) using 3D visualization software and assembled into a complete 3D skeletal model. The model was then rigged and animated using 3D animation and modeling software. The resulting 3D skeletal model can be used to characterize equine postures associated with degenerative tissue changes as well as to identify postures that reduce mechanical stress at the sites of tissue injury. In addition, when animated into 4D, the model can be used to demonstrate unhealthy and healthy skeletal movements and can be used to develop preventative and rehabilitative individualized therapies for horses with degenerative lamenesses. Although the model will soon be available for download, it is currently in a format that requires access to the 3D animation and modeling software, which has quite a learning curve for new users. This protocol will guide users in (1) developing such a model for any organism of interest and (2) using this specific equine model for their own research questions.

The purpose of this protocol is to describe the method of creation of a realistic, whole-body, skeletal model of a horse that can be used for functional anatomical and biomechanical modeling to characterize whole-body mechanics.

Therapies based upon whole-body biomechanical assessments are successful for injury prevention and rehabilitation in human athletes. Similar approaches ...