Journal of biomechanics
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Journal of biomechanics · Apr 2016
On the load-sharing along the ligamentous lumbosacral spine in flexed and extended postures: Finite element study.
A harmonic synergy between the load-bearing and stabilizing components of the spine is necessary to maintain its normal function. This study aimed to investigate the load-sharing along the ligamentous lumbosacral spine under sagittal loading. A 3D nonlinear detailed Finite Element (FE) model of lumbosacral spine with realistic geometry was developed and validated using wide range of numerical and experimental (in-vivo and in-vitro) data. ⋯ The ligaments withstood up to 67% and 81% of the total internal moment in cases of FL combined with EXT and FLX, respectively. Contribution of the facet joints in resisting internal force and moment was noticeable at levels L4-S1 only particularly in case of FL combined with EXT and reached up 29% and 52% of the internal moment and force, respectively. This study demonstrated that spinal load-sharing depended on applied load and varied along the spine.
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Journal of biomechanics · Apr 2016
Fluid-flow dependent response of intervertebral discs under cyclic loading: On the role of specimen preparation and preconditioning.
In vivo during the day, intervertebral discs are loaded mainly in compression causing fluid and height losses that are subsequently fully recovered overnight due to fluid inflow under smaller compression. However, in vitro, fluid flow through the endplates, in particular fluid imbibition, is hampered possibly by blood clots formed post mortem. Despite earlier in vitro studies, it remains yet unclear if and how fluid flow conditions in vitro could properly emulate those in vivo. ⋯ Results highlight the significant role of disc preload magnitude in disc height recovery during low loading periods. Attention should hence be given in future studies to the proper selection of preload magnitude and duration as well as the animal models used if in vivo response is intended to be replicated. Findings also indicate that flushing the endplates or injection of bone cement respectively neither facilitates nor impedes fluid flow into or out of the disc to a noticeable degree in this bovine disc model.
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Journal of biomechanics · Feb 2016
Biomechanical properties of lumbar endplates and their correlation with MRI findings of lumbar degeneration.
How stiffness and strength of the human lumbar endplate vary with location, spinal level, and its correlation with MRI findings of lumbar degeneration, has not been reported in detail. 27 lumbar spines (16 male, 11 female, 31-49yrs) were harvested from cadavers without history of lumbar lesion or trauma. Disc and endplate degeneration was evaluated from MRI. Micro-CT was used to evaluate endplate microstructure. ⋯ We conclude that endplate properties reflect compressive stresses within adjacent intervertebral discs. Weaker and softer endplates may indicate reduced mechanical loading in decompressed discs that are stress-shielded by the neural arch. Preoperative MRI evaluation of endplate integrity could reduce the risk of implant subsidence following inter-body fusion.
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Journal of biomechanics · Jan 2016
Mechanical testing and non-linear viscoelastic modelling of the human placenta in normal and growth restricted pregnancies.
Intrauterine Growth Restriction (IUGR) is a disease where the placenta is unable to transfer enough nutrients to the fetus, limiting its growth, and resulting in high mortality and life-long morbidities. Current detection rates of IUGR are poor, resulting in limited disease management. Elastography is a promising non-invasive tool for the detection of IUGR, and works by detecting changes in the mechanical properties of the placenta. To date, however, it is not known whether IUGR placentas have different mechanical properties from normal ones, and thus investigating this is the first focus of the current study. The second focus is to evaluate and model the viscoelastic properties of the normal and IUGR placenta, so that it may be possible to improve elastography in the future by incorporating viscoelasticity. ⋯ Our results demonstrate that IUGR placentae have different mechanical properties from normal placentae, and a five parameter bi-exponential NVS model can effectively describe the mechanical properties of the placenta in health and disease.
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Journal of biomechanics · Dec 2015
A machine learning approach to estimate Minimum Toe Clearance using Inertial Measurement Units.
Falls are the primary cause of accidental injuries (52%) and one of the leading causes of death in individuals aged 65 and above. More than 50% of falls in healthy older adults are due to tripping while walking. Minimum toe clearance (i.e., minimum height of the toe above the ground during the mid-swing phase - MTC) has been investigated as an indicator of tripping risk. ⋯ The GRNN based MTC height predictions demonstrated root-mean-square-error (RMSE) of 6.6mm with 9 optimum features for young adults and 7.1mm RMSE with 5 features for the older adults during treadmill walking. The GRNN based MTC height estimation method devised in this project represents approximately 68% less RMSE than other estimation techniques. The research findings show a strong potential for gait monitoring outside the laboratory to provide real-time MTC height information during everyday locomotion.