| 1. |
- Börlin, Niclas, 1968-, et al.
(author)
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The precision of radiostereometric measurements : manual vs. digital measurements
- 2002
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In: Journal of Biomechanics. - : Elsevier. - 0021-9290 .- 1873-2380. ; 35:1, s. 69-79
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Journal article (peer-reviewed)abstract
- The precision of digital vs. manual radiostereometric measurements in total hip arthroplasty was evaluated using repeated stereoradiographic exposures with an interval of 10–15 min. Ten Lubinus SP2 stems cemented into bone specimens and 12 patients with the same stem design were used to evaluate the precision of stem translations and rotations. The precision of translations and rotations of the cup and femoral head penetration was studied in 12 patients with whole polyethylene cups.The use of a measurement method based on digitised radiographs improved the precision for some of the motion parameters, whereas many of them did not change. A corresponding pattern was observed for both the intra- and interobserver error. Of the wear parameters, the most pronounced improvements were the 3D wear and in the proximal-distal direction, although the anterior-posterior precision was also improved. The mean errors of rigid body and elliptic fitting decreased in all evaluations but one, consistent with a more reproducible identification of the markers centres and the edge of the femoral head.Increased precision of radiostereometric measurements may be used to increase the statistical power of future randomised studies and to study new fields in orthopaedics requiring higher precision than has been available with RSA based on manual measurements.
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| 2. |
- Daggfeldt, Karl, et al.
(author)
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The mechanics of back-extensor torque production about the lumbar spine.
- 2003
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In: Journal of Biomechanics. - 0021-9290 .- 1873-2380. ; 36:6, s. 815-25
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Journal article (peer-reviewed)abstract
- The purpose of this study was to develop and evaluate a biomechanical model of lumbar back extension over a wide range of positions for the lumbar spine, incorporating the latest information on muscle geometry and intra-abdominal pressure (IAP). Analysis of the Visible Human data was utilised in order to obtain anatomical information unavailable from the literature and magnetic resonance imaging was used to generate subject-specific anatomical descriptions. The model was evaluated by comparisons with measured maximal voluntary static back-extension torques. Predicted maximal specific muscle tensions agreed well with in vitro measurements from the literature. When modelling the maximal static back-extension torque production, it was possible to come fairly close to simultaneous equilibrium about all the lumbar discs simply by a uniform muscle activation of all back-extensor muscles (the caudal part showed, however, less agreement). This indicates that equilibrium in the lumbar spine is mainly regulated by passive mechanical properties, e.g. muscle length changes due to postural changes, rather than due to complex muscle coordination, as earlier proposed. The model showed that IAP (measured during torque exertions) contributes about 10% of the total maximal voluntary back-extensor torque and that it can unload the spine from compression. The spinal unloading effect from the IAP was greatest with the spine held in a flexed position. This is in opposition to the effects of changed muscle lever arm lengths, which for a given load would give the largest spinal unloading in the extended position. These findings have implications for the evaluation of optimal lifting techniques.
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| 3. |
- Daggfeldt, Karl, et al.
(author)
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The role of intra-abdominal pressure in spinal unloading.
- 1997
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In: Journal of Biomechanics. - 0021-9290 .- 1873-2380. ; 30:11-12, s. 1149-55
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Journal article (peer-reviewed)abstract
- Previous studies on how an increase in intra-abdominal pressure (IAP) effects the loading of the lumbar spine during back extension show diverging results. From a critical review of the literature we deduce a simplified, but consistent, model of the mechanisms involved in IAP-induced unloading of the lumbar spine. The model is then expanded by explicitly incorporating equilibrium equations for the pressurised abdomen and the abdominal wall. It is shown that the unloading effect of IAP can be viewed as that of a pressurised column of fixed cross-sectional area, between the rib cage and pelvis. Different abdominal forms are examined and a form with zero longitudinal curvature is found to have some important mechanical benefits for the generation of IAP-induced alleviation of compressive loading of the lumbar spine.
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| 4. |
- Ekevad, Mats, et al.
(author)
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Influence of pole length and stiffness on the energy conversion in pole-vaulting
- 1997
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In: Journal of Biomechanics. - 0021-9290 .- 1873-2380. ; 30:3, s. 259-264
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Journal article (peer-reviewed)abstract
- An impact process similar to pole-vaulting is studied, viz., the impact in a vertical plane between the bottom end of a slightly eurved elastic bar (pole), with a point mass (vaulter) at the top end, and a rigid support (pole box). Before impact, the velocity of the pole and the vaulter forms a certain angle (take-off) with the horizontal ground. Finite element calculations of the trajectories of the vaulter are carried out, and a performance figure, defined as the ratio between the maximum potential energy of the vaulter and the initial kinetic energy of the vaulter and the pole, is determined as a function of dimensionaless parameters. As the vaulter remains passive during the vault, in contrast to a real vaulter, this performance figure is also the efficiency of conversion of the initial kinetic energy to the achieved potential energy in the vault. It is shown that, under normal pole-vault conditions, there exists a maximum performance figure with respect to pole length and stiffness. For an initial velocity and a body mass which are representative of an elite pole-vaulter, the maximum performance figure 0.87 is obtained for a pole with length 5.5 m.
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| 5. |
- Ekevad, Mats, et al.
(author)
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Simulation of 'smart' pole vaulting
- 1995
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In: Journal of Biomechanics. - : Elsevier BV. - 0021-9290 .- 1873-2380. ; 28:9, s. 1079-1090
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Journal article (peer-reviewed)abstract
- The process of pole vaulting is simulated using a finite element two-dimensional model of the pole and the vaulter. The pole is modelled with 20 beam elements and the vaulter with seven such elements linked together by pin joints. ‘Smart' behaviour is achieved through control of limited muscle torques at the joints according to a given strategy. This control strategy is such that the vaulter strives to carry through a prescribed sequence of motions, corresponding to a given style, during a vault. The optimum pole length is determined for a vaulter with given initial velocity, strength and style. When a pole of optimum length is used, the maximum increase of the potential energy of the vaulter is 1.27 times the initial kinetic energy of the vaulter and the pole. This shows that the contribution from muscle work to the increase in potential energy during a vault may be significant. The simulation method should be a useful tool for optimization of pole design. It might also be useful for optimization of vaulting style or for judging the importance of vaulter strength.
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| 6. |
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| 7. |
- Hodges, P W, et al.
(author)
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In vivo measurement of the effect of intra-abdominal pressure on the human spine.
- 2001
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In: Journal of Biomechanics. - 0021-9290 .- 1873-2380. ; 34:3, s. 347-53
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Journal article (peer-reviewed)abstract
- In humans, intra-abdominal pressure (IAP) is elevated during many everyday activities. This experiment aimed to investigate the extent to which increased IAP--without concurrent activity of the abdominal or back extensor muscles--produces an extensor torque. With subjects positioned in side lying on a swivel table with its axis at L3, moments about this vertebral level were measured when IAP was transiently increased by electrical stimulation of the diaphragm via the phrenic nerve. There was no electromyographic activity in abdominal and back extensor muscles. When IAP was increased artificially to approximately 15% of the maximum IAP amplitude that could be generated voluntarily with the trunk positioned in flexion, a trunk extensor moment (approximately 6 Nm) was recorded. The size of the effect was proportional to the increase in pressure. The extensor moment was consistent with that predicted from a model based on measurements of abdominal cross-sectional area and IAP moment arm. When IAP was momentarily increased while the trunk was flexed passively at a constant velocity, the external torque required to maintain the velocity was increased. These results provide the first in vivo data of the amplitude of extensor moment that is produced by increased IAP. Although the net effect of this extensor torque in functional tasks would be dependent on the muscles used to increase the IAP and their associated flexion torque, the data do provide evidence that IAP contributes, at least in part, to spinal stability.
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| 8. |
- Kleiven, Svein, et al.
(author)
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Consequences of head size following trauma to the human head
- 2002
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In: Journal of Biomechanics. - 0021-9290 .- 1873-2380. ; 35:2, s. 153-160
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Journal article (peer-reviewed)abstract
- The objective of the present study was to evaluate whether variation of human head size results in different outcome regarding intracranial responses following a direct impact. Finite Element models representing different head sizes and with various element mesh densities were created. Frontal impacts towards padded surfaces as well as inertial loads were analyzed. The variation in intracranial stresses and intracranial pressures for different sizes of the geometry and for various element meshes were investigated. A significant correlation was found between experiment and simulation with regard to intracranial pressure characteristics. The maximal effective stresses in the brain increased more than a fourfold, from 3.6 kPa for the smallest head size to 16.3 kPa for the largest head size using the same acceleration impulse. When simulating a frontal impact towards a padding, the head injury criterion (HIC) value varies from the highest level of 2433 at a head mass of 2.34 kg to the lowest level of 1376 at a head mass of 5.98 kg, contradicting the increase in maximal intracranial stresses with head size. The conclusion is that the size dependence of the intracranial stresses associated with injury, is not predicted by the HIC. It is suggested that variations in head size should be considered when developing new head injury criteria.
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| 9. |
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| 10. |
- Nyström, L., et al.
(author)
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A note on some identification problems arising in Roentgen stereo photogrammetric analysis
- 1994
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In: Journal of Biomechanics. - : Elsevier BV. - 0021-9290 .- 1873-2380. ; 27, s. 1291-1294
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Journal article (peer-reviewed)abstract
- When studying skeleton movements by using implanted landmarks and Roentgen Stereo Photogrammetric Analysis (RSA), some identification problems arise. One is to put the same label on a landmark at different examinations, another is to use the correct pairs of landmark images in order to compute a correct 3-D position of each landmark. We will present some methods that can be used as a support for solving these problems. We will also show how it is possible to detect and exclude landmarks that are loose and landmarks that have large measurement errors in their positions.
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| 11. |
- Parkkinen, Jyrki, et al.
(author)
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A mechanical apparatus with microprcessor controlled stress profile for cyclic compression of cultured articular cartilage explants
- 1989
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In: Journal of Biomechanics. - : Elsevier. - 0021-9290 .- 1873-2380. ; 22:11-12, s. 1285-1291
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Journal article (peer-reviewed)abstract
- An apparatus was designed for mechanical compression of cultured articular cartilage explants with a cylindrical plain-ended loading head (diameter 2–5 mm) driven by a stepping motor. A load cell under the culture dish was applied for feedback regulation utilizing a microprocessor-based control unit. The operating programs allowed either continuous or cyclic loading, the latter with adjustable loading/resting ratio. The improvements in the present design compared with previously described apparatuses for similar purposes include: (1) the accurately controlled compression by a load cell and a rapid feedback circuit; (2) the wide range of selectable stresses (25 kPa–12.5 MPa) with both continuous and cyclic loading modes; (3) the ability to handle cycles as short as 1 s with 15 ms peak loading phase. Using a 4s cycle and 0.5 MPa load for 1.5 h resulted in a significantly enhanced incorporation of radiosulphate in cultured bovine articular cartilage explants, suggesting a stimulation of proteoglycan synthesis. Light and scanning electron microscopic examinations revealed a slight depression and superficial alterations in cartilage structure at the impact site following high pressures. We expect that this apparatus will help in revealing how articular cartilage tissue and chondrocytes respond to external mechanical stimuli.
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| 12. |
- Schulze-Bauer, C. A. J., et al.
(author)
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Determination of constitutive equations for human arteries from clinical data
- 2003
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In: Journal of Biomechanics. - 0021-9290 .- 1873-2380. ; 36:2, s. 165-169
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Journal article (peer-reviewed)abstract
- Stress-strain analyses of vessel walls require appropriate constitutive equations. Determination of constitutive equations is based on experimental data of (i) diameter and length of a vessel segment subject to internal pressure and external axial force, and (ii) the load-free reference geometry. Typical clinical data, however, provide only pressure-diameter relations in the diastolic-systolic pressure range. In order to overcome this problem, an approach is proposed allowing the determination of constitutive equations from clinical data by means of reasonable assumptions regarding in situ configurations and stress states of arterial walls. The approach is based on a two-dimensional Fung-type stored-energy function capturing the characteristic nonlinear and anisotropic responses of arteries. Examples concerning human aortas from a normotensive and a hypertensive subject illustrate the potential of the approach.
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| 13. |
- Smedby, Örjan, et al.
(author)
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Development of femoral atherosclerosis in relation to flow disturbances.
- 1996
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In: Journal of Biomechanics. - : Elsevier BV. - 0021-9290 .- 1873-2380. ; 29:4, s. 543-547
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Journal article (peer-reviewed)abstract
- Angiography and post-mortem studies have indicated that disturbed blood flow may promote atherogenesis. Our aim was to demonstrate flow disturbances in vivo and correlate them to the subsequent development of atherosclerosis. The femoral arteries of 17 patients with early atherosclerosis were studied with cineangiography. The films are digitized and analyzed with an image analysis computer. From the time-intensity curves, the arrival time of the contrast medium at each pixel was calculated. In the resulting parametric images, the computer identified zones of delayed contrast filling, (ZDF) which have been shown to correspond to disturbed flow. The progression or regression of atherosclerosis was followed with another angiography 3 years later by computing changes in edge roughness. Arterial segments without flow disturbances (defined as ZDF) showed a more marked decrease in edge roughness than those with flow disturbances (p < 0.05). In addition, the edge roughness tended to increase more in segments with larger ZDF area. Angiographic studies of fluid mechanics and atherogenesis are feasible, but larger patient materials are needed.
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| 14. |
- Smedby, Örjan, et al.
(author)
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Flow disturbances in early femoral atherosclerosis : An in vivo study with digitized cineangiography
- 1993
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In: Journal of Biomechanics. - 0021-9290 .- 1873-2380. ; 26:9, s. 1105-1115
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Journal article (peer-reviewed)abstract
- Disturbances in arterial flow are believed to influence the localization and development of atherosclerotic plaques. The femoral arteries of 26 patients were studied with cineangiography, after which the films were digitized and analyzed with an image analysis computer. The image sequence was converted to a set of time-intensity curves, from which time parameters were calculated, representing the arrival time of the contrast medium at each pixel. In the resulting parametric images, zones of delayed contrast filling (ZDF) were identified by an adaptive thresholding, which identifies lighter regions within the vessel, excluding the smallest ones. The ZDF, which have been shown, in a model study, to correspond to disturbed flow, were more frequent in the inner curvature than in the outer curvature of the curved vessels. Accordingly, they were more frequent along the lateral wall than along the medial wall of the artery. Several ZDF were also found in the vicinity of bifurcations. Most of the findings tally closely with fluid mechanical theory. In future studies, flow disturbances are to be correlated with the progression of atherosclerotic lesions.
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| 15. |
- Söderkvist, Inge, et al.
(author)
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Determining the movements of the skeleton using well-configured markers
- 1993
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In: Journal of Biomechanics. - 0021-9290 .- 1873-2380. ; 26, s. 1473-1477
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Journal article (peer-reviewed)abstract
- The problem of determining skeletal movements in 3 dimensions by using a number of landmarks is treated. We present a method that determines the motion of a rigid body by using the positions of the landmarks in a least-squares sense. The method uses the singular value decomposition of a matrix derived from the positions of the landmarks. We show how one can use this method to express movement of skeleton segments relative to each other. As many others have pointed out, the movement can be very ill determined if the landmarks are badly configured. We present a condition number for the problem with good geometrical properties. The condition number depends on the configuration of the landmarks and indicates how to distribute the landmarks in a suitable way.
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| 16. |
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| 17. |
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| 18. |
- Turunen, Mikael, et al.
(author)
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Hyperosmolaric contrast agents in cartilage tomography may expose cartilage to overload-induced cell death.
- 2012
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In: Journal of Biomechanics. - : Elsevier. - 0021-9290 .- 1873-2380. ; 45:3, s. 497-503
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Journal article (peer-reviewed)abstract
- In clinical arthrographic examination, strong hypertonic contrast agents are injected directly into the joint space. This may reduce the stiffness of articular cartilage, which is further hypothesized to lead to overload-induced cell death. We investigated the cell death in articular cartilage while the tissue was compressed in situ in physiological saline solution and in full strength hypertonic X-ray contrast agent Hexabrix(TM). Samples were prepared from bovine patellae and stored in Dulbecco's Modified Eagle's Medium overnight. Further, impact tests with or without creep were conducted for the samples with contact stresses and creep times changing from 1 MPa to 10 MPa and from 0 min to 15 min, respectively. Finally, depth-dependent cell viability was assessed with a confocal microscope. In order to characterize changes in the biomechanical properties of cartilage as a result of the use of Hexabrix™, stress-relaxation tests were conducted for the samples immersed in Hexabrix™ and phosphate buffered saline (PBS). Both dynamic and equilibrium modulus of the samples immersed in Hexabrix™ were significantly (p<0.05) lower than those of the samples immersed in PBS. Cartilage samples immersed in physiological saline solution showed load-induced cell death primarily in the superficial and middle zones. However, under high 8-10 MPa contact stresses, the samples immersed in full strength Hexabrix™ showed significantly (p<0.05) higher number of dead cells than the samples compressed in physiological saline, especially in the deep zone of cartilage. In conclusion, excessive loading stresses followed by tissue creep might increase the risk for chondrocyte death in articular cartilage when immersed in hypertonic X-ray contrast agent, especially in the deep zone of cartilage.
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| 19. |
- Alvarez, Victor S, et al.
(author)
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Effect of pediatric growth on cervical spine kinematics and deformations in automotive crashes
- 2018
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In: Journal of Biomechanics. - : Elsevier. - 0021-9290 .- 1873-2380. ; 71, s. 76-83
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Journal article (peer-reviewed)abstract
- Finite element (FE) models are a powerful tool that can be used to understand injury mechanisms and develop better safety systems. This study aims to extend the understanding of pediatric spine biomechanics, where there is a paucity of studies available. A newly developed and continuously scalable FE model was validated and scaled to 1.5-, 3-, 6-, 10-, 14- and 18-year-old using a non-linear scaling technique, accounting for local topological changes. The oldest and youngest ages were also scaled using homogeneous geometric scaling. To study the effect of pediatric spinal growth on head kinematics and intervertebral disc strain, the models were exerted to 3.5 g acceleration pulse at the T1 vertebra to simulate frontal, rear and side impacts. It was shown that the head rotation increases with age, but is over predicted when geometrically scaling down from 18- to 1.5-year-old and under predicted when geometrically scaling up from 1.5- to 18-year-old. The strain in the disc, however, showed a clear decrease with age in side impact and for the upper cervical spine in rear impact, indicating a higher susceptibility for neck injury at younger ages. In the frontal impact, no clear age dependence could be seen, suggesting a large contribution from changed facet joint angles, and lower levels of strain, suggesting a lower risk of injury. The results also highlight the benefit of rearward facing children in a seat limiting head lateral motion.
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| 20. |
- Andersson, Magnus, et al.
(author)
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Characterization and estimation of turbulence-related wall shear stress in patient-specific pulsatile blood flow
- 2019
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In: Journal of Biomechanics. - : ELSEVIER SCI LTD. - 0021-9290 .- 1873-2380. ; 85, s. 108-117
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Journal article (peer-reviewed)abstract
- Disturbed, turbulent-like blood flow promotes chaotic wall shear stress (WSS) environments, impairing essential endothelial functions and increasing the susceptibility and progression of vascular diseases. These flow characteristics are today frequently detected at various anatomical, lesion and intervention-related sites, while their role as a pathological determinant is less understood. To present-day, numerous WSS-based descriptors have been proposed to characterize the spatiotemporal nature of the WSS disturbances, however, without differentiation between physiological laminar oscillations and turbulence-related WSS (tWSS) fluctuations. Also, much attention has been focused on magnetic resonance (MR) WSS estimations, so far with limited success; promoting the need of a near-wall surrogate marker. In this study, a new approach is explored to characterize the tWSS, by taking advantage of the tensor characteristics of the fluctuating WSS correlations, providing both a magnitude and an anisotropy measure of the disturbances. These parameters were studied in two patient-specific coarctation models (sever and mild), using large eddy simulations, and correlated against near-wall reciprocal Reynolds stress parameters. Collectively, results showed distinct regions of differing tWSS characteristics, features which were sensitive to changes in flow conditions. Generally, the post-stenotic tWSS was governed by near axisymmetric fluctuations, findings that where not consistent with conventional WSS disturbance predictors. At the 2-3 mm wall-offset range, a strong linear correlation was found between tWSS magnitude and near-wall turbulence kinetic energy (TKE), in contrast to the anisotropy indices, suggesting that MR-measured TKE can be used to assess elevated tWSS regions while tWSS anisotropy estimates request well-resolved simulation methods. (C) 2019 Elsevier Ltd. All rights reserved.
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| 21. |
- Andersson, Magnus, et al.
(author)
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Multidirectional WSS disturbances in stenotic turbulent flows: A pre- and post-intervention study in an aortic coarctation
- 2017
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In: Journal of Biomechanics. - : ELSEVIER SCI LTD. - 0021-9290 .- 1873-2380. ; 51
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Journal article (peer-reviewed)abstract
- Wall shear stress (WSS) disturbances are commonly expressed at sites of abnormal flow obstructions and may play an essential role in the pathogenesis of various vascular diseases. In laminar flows these disturbances have recently been assessed by the transverse wall shear stress (transWSS), which accounts for the WSS multidirectionality. Site-specific estimations of WSS disturbances in pulsatile transitional and turbulent type of flows are more challenging due to continuous and unpredictable changes in WSS behavior. In these complex flow settings, the transWSS may serve as a more comprehensive descriptor for assessing WSS disturbances of general nature compared to commonly used parameters. In this study large eddy simulations (LES) were used to investigate the transWSS properties in flows subjected to different pathological turbulent flow conditions, governed by a patient-specific model of an aortic coarctation pre and post balloon angioplasty. Results showed that regions of strong near-wall turbulence were collocated with regions of elevated transWSS and turbulent WSS, while in more transitional-like near-wall flow regions a closer resemblance was found between transWSS and low, and oscillatory WSS. Within the frame of this study, the transWSS parameter demonstrated a more multi-featured picture of WSS disturbances when exposed to different types of flow regimes, characteristics which were not depicted by the other parameters alone. (C) 2016 Published by Elsevier Ltd.
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| 22. |
- Arumugam, Ashokan, 1981-, et al.
(author)
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A novel test reliably captures hip and knee kinematics and kinetics during unanticipated/anticipated diagonal hops in individuals with anterior cruciate ligament reconstruction
- 2020
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In: Journal of Biomechanics. - : Elsevier. - 0021-9290 .- 1873-2380. ; 99
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Journal article (peer-reviewed)abstract
- Unanticipated land-and-cut maneuvers might emulate lower limb mechanics associated with anterior cruciate ligament (ACL) injury. Reliability studies on landing mechanics of such maneuvers are however lacking. This study investigated feasibility and within-session reliability of landing mechanics of a novel one-leg double-hop test, mimicking a land-and-cut maneuver, in individuals with ACL reconstruction (ACLR). Our test comprised a forward hop followed by a diagonal hop in either of two directions (medial/lateral) under anticipated and unanticipated conditions. Twenty individuals with a unilateral ACLR (aged 24.2 ± 4.2 years, 0.7-10.8 years post-surgery) performed three successful hops/direction per leg. We determined reliability (intraclass correlation coefficient [ICC]) and agreement (standard error of measurement [SEM]) of 3-dimensional hip and knee angles and moments during the deceleration phase of the land-and-cut maneuver (vulnerable for non-contact ACL injuries). Mean success rate for unanticipated hops was 71-77% and for anticipated hops 91-95%. Both limbs demonstrated moderate-excellent reliability (ICC 95% confidence intervals: 0.50-0.99) for almost all hip and knee peak angles and moments in all planes and conditions, with a few exceptions: poor-good reliability for hip and knee frontal and/or transverse plane variables, especially for lateral diagonal hops. The SEMs were ≤5° and ≤0.23 N·m/kg·m for most peak angles and moments, respectively. Our test seems feasible and showed satisfactory reliability for most hip and knee angles and moments; however, low knee abduction and internal rotation angles and moments, and moderate reliability of these moments deserve consideration. The test appears to challenge dynamic knee control and may prove valuable in evaluation during knee rehabilitation.
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| 23. |
- Arumugam, Ashokan, 1981-, et al.
(author)
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Introducing a novel test with unanticipated medial/lateral diagonal hops that reliably captures hip and knee kinematics in healthy women
- 2019
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In: Journal of Biomechanics. - : Elsevier. - 0021-9290 .- 1873-2380. ; 82, s. 70-79
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Journal article (peer-reviewed)abstract
- Despite a vast literature on one-leg hops and cutting maneuvers assessing knee control pre/post-injury of the anterior cruciate ligament (ACL), comprehensive and reliable tests performed under unpredictable conditions are lacking. This study aimed to: (1) assess the feasibility of an innovative, knee-challenging, one-leg double-hop test consisting of a forward hop followed by a diagonal hop (45°) performed medially (UMDH) or laterally (ULDH) in an unanticipated manner; and (2) determine within- and between-session reliability for 3-dimensional hip and knee kinematics and kinetics of these tests. Twenty-two healthy women (22.3 ± 3.3 years) performed three successful UMDH and ULDH, twice 1–4 weeks apart. Hop success rate was 69–84%. Peak hip and knee angles demonstrated moderate to excellent within-session reliability (intraclass correlation coefficient [ICC] 95% confidence interval [CI]: 0.67–0.99, standard error of measurement [SEM] ≤ 3°) and poor to excellent between-session reliability (ICC CI: 0.22–0.94, SEM ≤ 3°) for UMDH and ULDH. The smallest real difference (SRD) was low (≤ 5°) for nearly all peak angles. Peak hip and knee moments demonstrated poor to excellent reliability (ICC CI: 0–0.97) and, in general, moments were more reliable within-session (SEM ≤ 0.14 N.m/kg.m, both directions) than between-session (SRD ≤ 0.43 N.m/kg.m). Our novel test was feasible and, in most but not all cases, provided reliable angle estimates (within-session > between-session, both directions) albeit less reliable moments (within-session > between-session, both directions). The relatively large hip and knee movements in the frontal and transverse planes during the unanticipated hops suggest substantial challenge of dynamic knee control. Thus, the test seems appropriate for evaluating knee function during ACL injury rehabilitation.
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| 24. |
- Begon, Mickaël, et al.
(author)
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Can optimal marker weightings improve thoracohumeral kinematics accuracy?
- 2015
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In: Journal of Biomechanics. - : Elsevier BV. - 0021-9290 .- 1873-2380. ; 48:10, s. 2019-2025
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Journal article (peer-reviewed)abstract
- Local and global optimization algorithms have been developed to estimate joint kinematics to reducing soft movement artifact (STA). Such algorithms can include weightings to account for different STA occur at each marker. The objective was to quantify the benefit of optimal weighting and determine if optimal marker weightings can improve humerus kinematics accuracy. A pin with five reflective markers was inserted into the humerus of four subjects. Seven markers were put on the skin of the arm. Subjects performed 38 different tasks including arm elevation, rotation, daily-living tasks, and sport activities. In each movement, mean and peak errors in skin- vs. pins-orientation were reported. Then, optimal marker weightings were found to best match skin- and pin-based orientation. Without weighting, the error of the arm orientation ranged from 1.9° to 17.9°. With weighting, 100% of the trials were improved and the average error was halved. The mid-arm markers weights were close to 0 for three subjects. Weights of a subject applied to the others for a given movement, and weights of a movement applied to others for a given subject did not systematically increased accuracy of arm orientation. Without weighting, a redundant set of marker and least square algorithm improved accuracy to estimate arm orientation compared to data of the literature using electromagnetic sensor. Weightings were subject- and movement-specific, which reinforces that STA are subject- and movement-specific. However, markers on the deltoid insertion and on lateral and medial epicondyles may be preferred if a limited number of markers is used.
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| 25. |
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