| 1. |
- Grassi, Lorenzo, et al.
(författare)
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3D Finite Element Models Reconstructed From 2D Dual-Energy X-Ray Absorptiometry (DXA) Images Improve Hip Fracture Prediction Compared to Areal BMD in Osteoporotic Fractures in Men (MrOS) Sweden Cohort
- 2023
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Ingår i: Journal of Bone and Mineral Research. - : John Wiley & Sons. - 0884-0431 .- 1523-4681. ; 38:9, s. 1258-1267
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Tidskriftsartikel (refereegranskat)abstract
- Bone strength is an important contributor to fracture risk. Areal bone mineral density (aBMD) derived from dual-energy X-ray absorptiometry (DXA) is used as a surrogate for bone strength in fracture risk prediction tools. 3D finite element (FE) models predict bone strength better than aBMD, but their clinical use is limited by the need for 3D computed tomography and lack of automation. We have earlier developed amethod to reconstruct the 3D hip anatomy froma 2D DXA image, followed by subject-specific FE-based prediction of proximal femoral strength. In the current study, we aim to evaluate the method's ability to predict incident hip fractures in a populationbased cohort (Osteoporotic Fractures in Men [MrOS] Sweden). We defined two subcohorts: (i) hip fracture cases and controls cohort: 120men with a hip fracture (<10 years frombaseline) and two controls to each hip fracture case, matched by age, height, and body mass index; and (ii) fallers cohort: 86men who had fallen the year before their hip DXA scan was acquired, 15 of which sustained a hip fracture during the following 10 years. For each participant, we reconstructed the 3D hip anatomy and predicted proximal femoral strength in 10 sideways fall configurations using FE analysis. The FE-predicted proximal femoral strength was a better predictor of incident hip fractures than aBMD for both hip fracture cases and controls (difference in area under the receiver operating characteristics curve, Delta AUROC = 0.06) and fallers (Delta AUROC = 0.22) cohorts. This is the first time that FE models outperformed aBMD in predicting incident hip fractures in a population-based prospectively followed cohort based on 3D FE models obtained from a 2D DXA scan. Our approach has potential to notably improve the accuracy of fracture risk predictions in a clinically feasible manner (only one single DXA image is needed) and without additional costs compared to the current clinical approach.
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| 2. |
- Grassi, Lorenzo, et al.
(författare)
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3d Finite Element Models Reconstructed From 2d Dxa Images Improve Hip Fracture Prediction Compared to Areal Bmd in Mros Sweden Cohort
- 2023
-
Ingår i: Journal of Bone and Mineral Research. - 1523-4681. ; 38:9, s. 1258-1267
-
Tidskriftsartikel (refereegranskat)abstract
- Bone strength is an important contributor to fracture risk. Areal bone mineral density (aBMD) derived from dual-energy X-ray absorptiometry (DXA) is used as a surrogate for bone strength in fracture risk prediction tools. 3D finite element (FE) models predict bone strength better than aBMD, but their clinical use is limited by the need for 3D computed tomography and lack of automation. We have earlier developed a method to reconstruct the 3D hip anatomy from a 2D DXA image, followed by subject-specific FE-based prediction of proximal femoral strength. In the current study, we aim to evaluate the method's ability to predict incident hip fractures in a population-based cohort (MrOS Sweden). We defined two sub-cohorts: (i) hip fracture cases and controls cohort: 120 men with a hip fracture (<10 years from baseline) and 2 controls to each hip fracture case, matched by age, height, and body mass index; (ii) fallers cohort: 86 men who had fallen the year before their hip DXA scan was acquired, 15 of which sustained a hip fracture during the following 10 years. For each participant, we reconstructed the 3D hip anatomy and predicted proximal femoral strength in 10 sideways fall configurations using FE analysis. The FE-predicted proximal femoral strength was a better predictor of incident hip fractures than aBMD for both hip fracture cases and controls (difference in area under the receiver operating characteristics curve, ΔAUROC = 0.06) and fallers (ΔAUROC = 0.22) cohorts. This is the first time that FE models outperform aBMD in predicting incident hip fractures in a population-based prospectively followed cohort based on 3D FE models obtained from a 2D DXA scan. Our approach has potential to notably improve the accuracy of fracture risk predictions in a clinically feasible manner (only one single DXA image is needed) and without additional costs compared to the current clinical approach.
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| 3. |
- Grassi, Lorenzo, et al.
(författare)
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Elucidating failure mechanisms in human femurs during a fall to the side using bilateral digital image correlation
- 2020
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Ingår i: Journal of Biomechanics. - : Elsevier BV. - 0021-9290. ; 106
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Tidskriftsartikel (refereegranskat)abstract
- An improved understanding of the mechanical properties of human femurs is a milestone towards a more accurate assessment of fracture risk. Digital image correlation (DIC) has recently been adopted to provide full-field strain measurements during mechanical testing of femurs. However, it has typically been used to measure strains on the anterior side of the femur, whereas in both single-leg-stance and sideways fall loading conditions, the highest deformations result on the medial and lateral sides of the femoral neck. The goal of this study was to measure full-field deformations simultaneously on the medial and lateral side of the femoral neck in a configuration resembling a fall to the side. Twelve female cadaver femurs were prepared for DIC measurements and tested in sideways fall at 5 mm/s displacement rate. Two pairs of cameras recorded the medial and lateral side of the femoral neck, and deformations were calculated using DIC. The samples exhibited a two-stage failure: first, a compressive collapse on the superolateral side of the femoral neck in conjunction with peak force, followed by complete femoral neck fracture at the force drop following the post-elastic phase. DIC measurements corroborated this observation by reporting no tensile strains above yield limit for the medial side of the neck up to peak force. DIC measurements registered onto the bone micro-architecture showed strain localizations in proximity of cortical pores due to, for instance, blood vessels. This could explain previously reported discrepancies between simulations and experiments in regions rich with large pores, like the superolateral femoral neck.
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| 4. |
- Grassi, Lorenzo, et al.
(författare)
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Experimental Validation Of Finite Element Model For Proximal Composite Femur Using Optical Measurements
- 2013
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Ingår i: Journal of the Mechanical Behavior of Biomedical Materials. - : Elsevier BV. - 1751-6161. ; 21, s. 86-94
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Tidskriftsartikel (refereegranskat)abstract
- Patient-specific finite element models have been used to predict femur strength and fracture risk in individuals. Validation of the adopted finite element modelling procedure against mechanical testing data is a crucial step when aiming for clinical applications. The majority of the works available in literature used data from strain gages to validate the model, thus having up to 15 experimental measurements. Optical techniques, such as Digital Image Correlation, can help to improve the models by providing a continuous field of deformation data over a femoral surface. The main objective of this study was to validate finite element models of six composite femora against strain data from digital image correlation, obtained during fracture tests performed in quasi-axial loading configuration. The finite element models were obtained from CT scans, by means of a semi-automatic segmentation. The principal strains both during the elastic phase and close to the fracture were compared, and showed a correlation coefficient close to 0.9. In the linear region, the slope and intercept were close to zero and unity, while for the case when fracture load was simulated, the slope decreased somewhat. The accuracy of the obtained results is comparable with the state-of-the-art literature, with the significant improvement of having around 50000 data points for each femur. This large number of measurements allows a more comprehensive validation of the predictions by the finite element models, since thousand of points are tracked along the femoral neck and trochanter region, i.e., the sites that are most critical for femur fracture. Moreover, strain measurement biases due to the strain gage reinforcement effect, were avoided. The combined experimental-numerical approach proved to be ready for application to in-vitro tests of human cadaver femurs, thus helping to develop a suitable mechanistic fracture risk criterion.
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| 5. |
- Grassi, Lorenzo, et al.
(författare)
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Full-field Strain Measurement During Mechanical Testing of the Human Femur at Physiologically Relevant Strain Rates
- 2014
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Ingår i: Journal of Biomechanical Engineering. - : ASME International. - 0148-0731 .- 1528-8951. ; 136:11
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the mechanical properties of human femora is of great importance for the development of a reliable fracture criterion aimed at assessing fracture risk. Earlier ex vivo studies have been conducted by measuring strains on a limited set of locations using strain gauges. Digital Image Correlation (DIC) could instead be used to reconstruct the full-field strain pattern over the surface of the femur. The objective of this study was to measure the full-field strain response of cadaver femora tested at a physiological strain rate up to fracture in a configuration resembling single stance. The three cadaver femora were cleaned from soft tissues, and a white background paint was applied with a random black speckle pattern over the anterior surface. The mechanical tests were conducted up to fracture at a constant displacement rate of 15 mm/s, and two cameras recorded the event at 3000 frames per second. DIC was performed to retrieve the full-field displacement map, from which strains were derived. A low-pass filter was applied over the measured displacements before the crack opened in order to reduce the noise level. The noise levels were assessed using a dedicated control plate. Conversely, no filtering was applied at the frames close to fracture to get the maximum resolution. The specimens showed a linear behavior of the principal strains with respect to the applied force up to fracture. The strain rate was comparable to the values available in literature from in-vivo measurements during daily activities. The cracks opened and fully propagated in less than 1 ms, and small regions with high values of the major principal strains could be spotted just a few frames before the crack opened. This corroborates the hypothesis of a strain-driven fracture mechanism in human bone. The data represents a comprehensive collection of full-field strains, both at physiological load levels and up to fracture. About 10000 measurements were collected for each bone, providing superior spatial resolution compared to ~15 measurements typically collected using strain gauges. These experimental data collection can be further used for validation of numerical models, and for experimental verification of bone constitutive laws and fracture criteria.
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| 6. |
- Grassi, Lorenzo, et al.
(författare)
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How accurately can subject-specific finite element models predict strains and strength of human femora? Investigation using full-field measurements
- 2016
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Ingår i: Journal of Biomechanics. - : Elsevier BV. - 1873-2380 .- 0021-9290. ; 49:5, s. 802-806
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Tidskriftsartikel (refereegranskat)abstract
- Subject-specific finite element models have been proposed as a tool to improve fracture risk assessment in individuals. A thorough laboratory validation against experimental data is required before introducing such models in clinical practice. Results from digital image correlation can provide full-field strain distribution over the specimen surface during in vitro test, instead of at a few pre-defined locations as with strain gauges. The aim of this study was to validate finite element models of human femora against experimental data from three cadaver femora, both in terms of femoral strength and of the full-field strain distribution collected with digital image correlation. The results showed a high accuracy between predicted and measured principal strains (R2=0.93, RMSE=10%, 1600 validated data points per specimen). Femoral strength was predicted using a rate dependent material model with specific strain limit values for yield and failure. This provided an accurate prediction (<2% error) for two out of three specimens. In the third specimen, an accidental change in the boundary conditions occurred during the experiment, which compromised the femoral strength validation. The achieved strain accuracy was comparable to that obtained in state-of-the-art studies which validated their prediction accuracy against 10–16 strain gauge measurements. Fracture force was accurately predicted, with the predicted failure location being very close to the experimental fracture rim. Despite the low sample size and the single loading condition tested, the present combined numerical-experimental method showed that finite element models can predict femoral strength by providing a thorough description of the local bone mechanical response.
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| 7. |
- Grassi, Lorenzo, et al.
(författare)
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Statistical Shape and Appearance Models : Development Towards Improved Osteoporosis Care
- 2021
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Ingår i: Current Osteoporosis Reports. - : Springer Science and Business Media LLC. - 1544-1873 .- 1544-2241. ; 19:6, s. 676-687
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Forskningsöversikt (refereegranskat)abstract
- PURPOSE OF REVIEW: Statistical models of shape and appearance have increased their popularity since the 1990s and are today highly prevalent in the field of medical image analysis. In this article, we review the recent literature about how statistical models have been applied in the context of osteoporosis and fracture risk estimation.RECENT FINDINGS: Recent developments have increased their ability to accurately segment bones, as well as to perform 3D reconstruction and classify bone anatomies, all features of high interest in the field of osteoporosis and fragility fractures diagnosis, prevention, and treatment. An increasing number of studies used statistical models to estimate fracture risk in retrospective case-control cohorts, which is a promising step towards future clinical application. All the reviewed application areas made considerable steps forward in the past 5-6 years. Heterogeneities in validation hinder a thorough comparison between the different methods and represent one of the future challenges to be addressed to reach clinical implementation.
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| 8. |
- Grassi, Lorenzo, et al.
(författare)
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Validation of 3d finite element models from simulated Dxa images for Biofidelic simulations of sideways fall impact to the hip
- 2020
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Ingår i: Bone. - : Elsevier BV. - 1873-2763 .- 8756-3282. ; 142
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Tidskriftsartikel (refereegranskat)abstract
- Computed tomography (CT)-derived finite element (FE) models have been proposed as a tool to improve the current clinical assessment of osteoporosis and personalized hip fracture risk by providing an accurate estimate of femoral strength. However, this solution has two main drawbacks, namely: (i) 3D CT images are needed, whereas 2D dual-energy x-ray absorptiometry (DXA) images are more generally available, and (ii) quasi-static femoral strength is predicted as a surrogate for fracture risk, instead of predicting whether a fall would result in a fracture or not. The aim of this study was to combine a biofidelic fall simulation technique, based on 3D computed tomography (CT) data with an algorithm that reconstructs 3D femoral shape and BMD distribution from a 2D DXA image. This approach was evaluated on 11 pelvis-femur constructs for which CT scans, ex vivo sideways fall impact experiments and CT-derived biofidelic FE models were available. Simulated DXA images were used to reconstruct the 3D shape and bone mineral density (BMD) distribution of the left femurs by registering a projection of a statistical shape and appearance model with a genetic optimization algorithm. The 2D-to-3D reconstructed femurs were meshed, and the resulting FE models inserted into a biofidelic FE modeling pipeline for simulating a sideways fall. The median 2D-to-3D reconstruction error was 1.02 mm for the shape and 0.06 g/cm3 for BMD for the 11 specimens. FE models derived from simulated DXAs predicted the outcome of the falls in terms of fracture versus non-fracture with the same accuracy as the CT-derived FE models. This study represents a milestone towards improved assessment of hip fracture risk based on widely available clinical DXA images.
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| 9. |
- Khayyeri, Hanifeh, et al.
(författare)
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A novel semi-automatic hip morphology assessment tool is more accurate than manual radiographic evaluations
- 2020
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Ingår i: Computer Methods in Biomechanics and Biomedical Engineering: Imaging and Visualization. - : Informa UK Limited. - 2168-1163 .- 2168-1171. ; 8:1, s. 76-86
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Tidskriftsartikel (refereegranskat)abstract
- Radiological and pathological characteristics of hip osteoarthritis (OA) is joint-space loss due to degradation of articular cartilage. However, patients with early-stage OA do not yet show any radiological signs, which leaves them without diagnosis and treatment. This study evaluates the potential of a novel tool to identify pre-radiographic OA changes based on hip bone morphology. Two statistical appearance models for femur and pelvis were used to estimate the 3Dmorphology of the hip bones based on planar radiographs from patients. Well-known hip geometrical parameters (n = 22) were computed from patient CT scans (truth), 3D reconstructions (new method) and radiographs (calculated manually). The methods were compared by measuring relative error to truth. The new method was significantly more accurate in calculating hip geometrical parameters than the manual 2D calculations. The proposed approach could also capture rotational parameters like cross-over sign and anterior wall sign (100% correct predictions). The method can successfully reconstruct 3D hip shapes and densities for patients that have not yet developed severe osteoarthritis, and provided higher precision than manual estimations. Thus, it may be used to calculate morphological parameters that are predictors of OA and can become a powerful tool in human hip OA research and diagnostics.
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| 10. |
- Väänänen, Sami P, et al.
(författare)
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Automated segmentation of cortical and trabecular bone to generate finite element models for femoral bone mechanics
- 2019
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Ingår i: Medical Engineering & Physics. - : Elsevier BV. - 1873-4030 .- 1350-4533. ; 70:August 2019, s. 19-28
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Tidskriftsartikel (refereegranskat)abstract
- Finite element (FE) models based on quantitative computed tomography (CT) images are better predictors of bone strength than conventional areal bone mineral density measurements. However, FE models require manual segmentation of the femur, which is not clinically applicable. This study developed a method for automated FE analyses from clinical CT images. Clinical in-vivo CT images of 13 elderly female subjects were collected to evaluate the method. Secondly, proximal cadaver femurs were harvested and imaged with clinical CT (N = 17). Of these femurs, 14 were imaged with µCT and three had earlier been tested experimentally in stance-loading, while collecting surface deformations with digital image correlation. Femurs were segmented from clinical CT images using an automated method, based on the segmentation tool Stradwin. The method automatically distinguishes trabecular and cortical bone, corrects partial volume effect and generates input for FE analysis. The manual and automatic segmentations agreed within about one voxel for in-vivo subjects (0.99 ± 0.23 mm) and cadaver femurs (0.21 ± 0.07 mm). The strains from the FE predictions closely matched with the experimentally measured strains (R2 = 0.89). The method can automatically generate meshes suitable for FE analysis. The method may bring us one step closer to enable clinical usage of patient-specific FE analyses.
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