In JoVE (3)
- Proximal Cadaveric Femur Preparation for Fracture Strength Testing and Quantitative CT-based Finite Element Analysis
- Method and Instrumented Fixture for Femoral Fracture Testing in a Sideways Fall-on-the-Hip Position
- A Method to Estimate Cadaveric Femur Cortical Strains During Fracture Testing Using Digital Image Correlation
Articles by Timothy Rossman in JoVE
Proximal Cadaveric Femur Preparation for Fracture Strength Testing and Quantitative CT-based Finite Element Analysis Dan Dragomir-Daescu1,2, Asghar Rezaei1,2, Susheil Uthamaraj2, Timothy Rossman2, James T. Bronk3, Mark Bolander3, Vincent Lambert2, Sean McEligot2, Rachel Entwistle2, Hugo Giambini3, Iwona Jasiuk4, Michael J. Yaszemski3, Lichun Lu1,3 1Department of Physiology and Biomedical Engineering, Mayo Clinic, 2Division of Engineering, Mayo Clinic, 3Department of Orthopedic Surgery, Mayo Clinic, 4Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign We present a robust protocol on how to carefully preserve and prepare cadaveric femora for fracture testing and quantitative computed tomography imaging. The method provides precise control over input conditions for the purpose of determining relationships between bone mineral density, fracture strength, and defining finite element model geometry and properties.
Method and Instrumented Fixture for Femoral Fracture Testing in a Sideways Fall-on-the-Hip Position Dan Dragomir-Daescu1,2, Asghar Rezaei1,2, Timothy Rossman2, Susheil Uthamaraj2, Rachel Entwistle2, Sean McEligot2, Vincent Lambert2, Hugo Giambini3, Iwona Jasiuk4, Michael J. Yaszemski3, Lichun Lu1,3 1Department of Physiology and Biomedical Engineering, Mayo Clinic, 2Division of Engineering, Mayo Clinic, 3Department of Orthopedic Surgery, Mayo Clinic, 4Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign 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.
A Method to Estimate Cadaveric Femur Cortical Strains During Fracture Testing Using Digital Image Correlation Timothy Rossman1, Susheil Uthamaraj1, Asghar Rezaei1,2, Sean McEligot1, Hugo Giambini3, Iwona Jasiuk4, Michael J. Yaszemski3, Lichun Lu3, Dan Dragomir-Daescu1,2 1Division of Engineering, Mayo Clinic, 2Department of Physiology and Biomedical Engineering, Mayo Clinic, 3Department of Orthopedic Surgery, Mayo Clinic, 4Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign 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.
Other articles by Timothy Rossman on PubMed
Intra-aneurysmal Flow Rates Are Reduced by Two Flow Diverters: an Experiment Using Tomographic Particle Image Velocimetry in an Aneurysm Model Journal of Neurointerventional Surgery. Oct, 2014 | Pubmed ID: 25280567 Limitations on treating large, giant, and wide-necked aneurysms with coiling have made flow diverters a promising alternative to current practice by supporting reconstruction of the parent artery.
Quantitative Computed Tomography-based Finite Element Analysis Predictions of Femoral Strength and Stiffness Depend on Computed Tomography Settings Journal of Biomechanics. Jan, 2015 | Pubmed ID: 25442008 The aim of the present study was to compare proximal femur strength and stiffness obtained experimentally with estimations from Finite Element Analysis (FEA) models derived from Quantitative Computed Tomography (QCT) scans acquired at two different scanner settings. QCT/FEA models could potentially aid in diagnosis and treatment of osteoporosis but several drawbacks still limit their predictive ability. One potential reason is that the models are still sensitive to scanner settings which could lead to changes in assigned material properties, thus limiting their results accuracy and clinical effectiveness. To find the mechanical properties we fracture tested 44 proximal femora in a sideways fall-on-the-hip configuration. Before testing, we CT scanned all femora twice, first at high resolution scanner settings, and second at low resolution scanner settings and built 88 QCT/FEA models of femoral strength and stiffness. The femoral set neck bone mineral density, as measured by DXA, uniformly covered the range from osteoporotic to normal. This study showed that the femoral strength and stiffness values predicted from high and low resolution scans were significantly different (p
QCT/FEA Predictions of Femoral Stiffness Are Strongly Affected by Boundary Condition Modeling Computer Methods in Biomechanics and Biomedical Engineering. Mar, 2015 | Pubmed ID: 25804260 Quantitative computed tomography-based finite element models of proximal femora must be validated with cadaveric experiments before using them to assess fracture risk in osteoporotic patients. During validation, it is essential to carefully assess whether the boundary condition (BC) modeling matches the experimental conditions. This study evaluated proximal femur stiffness results predicted by six different BC methods on a sample of 30 cadaveric femora and compared the predictions with experimental data. The average stiffness varied by 280% among the six BCs. Compared with experimental data, the predictions ranged from overestimating the average stiffness by 65% to underestimating it by 41%. In addition, we found that the BC that distributed the load to the contact surfaces similar to the expected contact mechanics predictions had the best agreement with experimental stiffness. We concluded that BC modeling introduced large variations in proximal femora stiffness predictions.
A Method for Accounting for Test Fixture Compliance when Estimating Proximal Femur Stiffness Journal of Biomechanics. Sep, 2016 | Pubmed ID: 27521186 Fracture testing of cadaveric femora to obtain strength and stiffness information is an active area of research in developing tools for diagnostic prediction of bone strength. These measurements are often used in the estimation and validation of companion finite element models constructed from the femora CT scan data, therefore, the accuracy of the data is of paramount importance. However, experimental stiffness calculated from force-displacement data has largely been ignored by most researchers due to inherent error in the differential displacement measurement obtained when not accounting for testing apparatus compliance. However, having such information is necessary for validation of computational models. Even in the few cases when fixture compliance was considered the measurements showed large lab-to-lab variation due to lack of standardization in fixture design. We examined the compliance of our in-house designed cadaveric femur test fixture to determine the errors we could expect when calculating stiffness from the collected experimental force-displacement data and determined the stiffness of the test fixture to be more than 10 times the stiffness of the stiffest femur in a sample of 44 femora. When correcting the apparent femur stiffness derived from the original data, we found that the largest stiffness was underestimated by about 10%. The study confirmed that considering test fixture compliance is a necessary step in improving the accuracy of fracture test data for characterizing femur stiffness, and highlighted the need for test fixture design standardization for proximal femur fracture testing.