| 1. |
- Grassi, Lorenzo, et al.
(författare)
-
Prediction of femoral strength using 3D finite element models reconstructed from DXA images: validation against experiments
- 2017
-
Ingår i: Biomechanics and Modeling in Mechanobiology. - : Springer Science and Business Media LLC. - 1617-7940 .- 1617-7959. ; 16:3, s. 989-1000
-
Tidskriftsartikel (refereegranskat)abstract
- Computed tomography (CT)-based finite element (FE) models may improve the current osteoporosis diagnostics and prediction of fracture risk by providing an estimate for femoral strength. However, the need for a CT scan, as opposed to the conventional use of dual-energy X-ray absorptiometry (DXA) for osteoporosis diagnostics, is considered a major obstacle. The 3D shape and bone mineral density (BMD) distribution of a femur can be reconstructed using a statistical shape and appearance model (SSAM) and the DXA image of the femur. Then, the reconstructed shape and BMD could be used to build FE models to predict bone strength. Since high accuracy is needed in all steps of the analysis, this study aimed at evaluating the ability of a 3D FE model built from one 2D DXA image to predict the strains and fracture load of human femora. Three cadaver femora were retrieved, for which experimental measurements from ex vivo mechanical tests were available. FE models were built using the SSAM-based reconstructions: using only the SSAM-reconstructed shape, only the SSAM-reconstructed BMD distribution, and the full SSAM-based reconstruction (including both shape and BMD distribution). When compared with experimental data, the SSAM-based models predicted accurately principal strains (coefficient of determination >0.83, normalized root-mean-square error <16%) and femoral strength (standard error of the estimate 1215 N). These results were only slightly inferior to those obtained with CT-based FE models, but with the considerable advantage of the models being built from DXA images. In summary, the results support the feasibility of SSAM-based models as a practical tool to introduce FE-based bone strength estimation in the current fracture risk diagnostics.
|
|
| 2. |
- Vaananen, Sami P., et al.
(författare)
-
Estimation of 3D rotation of femur in 2D hip radiographs
- 2012
-
Ingår i: Journal of Biomechanics. - : Elsevier BV. - 1873-2380 .- 0021-9290. ; 45:13, s. 2279-2283
-
Tidskriftsartikel (refereegranskat)abstract
- Femoral radiographs are affected by the degree of rotation of the femur with respect to the plane of projection. We aimed to determine the 3D rotation of the proximal femur in 2D radiographs. A 3D Statistical Appearance Model (SAM), which was built from CT images of cadaver proximal femurs (n = 33) was randomly sampled to form a training set of 500 bones. Nineteen clinical CT images were collected for testing. All CT images were rotated to +/- 20 degrees in 2 degrees division around the shaft axis, +/- 10 degrees around medial-lateral axis, and by simultaneous rotation of both axes (+/- 16 degrees and +/- 8 degrees around shaft and medial-lateral axes). In each orientation, a 2D projection was recorded for generating a 2D SAM. The outcome parameters of the 2D SAM were used as input for a linear regression model and an artificial neural network to predict the rotation. The artificial neural network estimated the rotation more accurately than the linear regression. For artificial neural networks the mean errors were 4.0 degrees and 2.0 degrees around the shaft and medial-lateral axes, respectively. For an individual radiograph, the confidence interval of estimation was still relatively large. However, this method has high potential to differentiate the amount of rotations in two image sets. (C) 2012 Elsevier Ltd. All rights reserved.
|
|
| 3. |
- Vaananen, Sami P., et al.
(författare)
-
Repeatability of digital image correlation for measurement of surface strains in composite long bones
- 2013
-
Ingår i: Journal of Biomechanics. - : Elsevier BV. - 1873-2380 .- 0021-9290. ; 46:11, s. 1928-1932
-
Tidskriftsartikel (refereegranskat)abstract
- Digital image correlation (DIC) can measure full-field surface strains during mechanical testing of hard and soft tissues. When compared to traditional methods, such as strain gauges, DIC offers larger validation data (similar to 50,000 points) for, e.g., finite element models. Our main aim was to evaluate the repeatability of surface strain measurements with DIC during compressive testing of composite femurs mimicking human bones. We also studied the similarity of the composite femur samples using CT. Composite femurs were chosen as test material to minimize the uncertainties associated with the use of cadaveric tissues and to understand the variability of the DIC measurement itself. Six medium-sized fourth generation composite human proximal femora (Sawbones) were CT imaged and mechanically tested in stance configuration. The force-displacement curves were recorded and the 3D surface strains were measured with DIC on the anterior surface of the femurs. Five femurs fractured at the neck-trochanter junction and one at the site below the minor trochanter. CT image of this bone showed an air cavity at the initial fracture site. All femurs fractured through a sudden brittle crack. The fracture force for the composite bones was 5751 +/- 650 N (mean +/- SD). The maximum von Mises strain during the fractures was 2.4 +/- 0.8%. Noise in one experiment was 5-30 mu epsilon. When applied loads were equalized the variation in strains between the bones was 20-25%, and when the maximum strains were equalized, variation in the other regions was 5-10%. DIC showed that the ability of nominally identical composite bones to bear high strains and loads before fracturing may vary between the samples. (C) 2013 Elsevier Ltd. All rights reserved.
|
|
