Journal of biomechanics
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Finite element (FE) models are used to identify head injury mechanisms and design new and improved injury prevention schemes. Although brain-skull boundary conditions strongly influence the model mechanical responses, limited experimental data are available to develop an informed representation. We hypothesize that the spinal cord tension and gravity contribute to the pons displacement in vivo. ⋯ By comparing images before and after the motion, we found that while the rotation of the pons is negligible relative to the skull, the pons displaces significantly at the foramen magnum, on the order of approximately 2 mm. When the spinal cord tension and gravity act in concert, the pons moves caudally; when opposed, superiorly, such that the influence of gravity on the pons is six times that of the spinal cord tension. Based on these findings, we recommend that the brainstem-skull interface be treated as a sliding (with or without friction) boundary condition in FE models of the human head.
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Journal of biomechanics · Jan 2007
Cervical facet capsular ligament yield defines the threshold for injury and persistent joint-mediated neck pain.
The cervical facet joint has been identified as a source of neck pain, and its capsular ligament is a likely candidate for injury during whiplash. Many studies have shown that the mechanical properties of ligaments can be altered by subfailure injury. However, the subfailure mechanical response of the facet capsular ligament has not been well defined, particularly in the context of physiology and pain. ⋯ Ligament yield point occurred at a distraction magnitude in which pain symptoms begin to appear in vivo in the rat. These mechanical findings provide insight into the relationship between gross structural failure and painful loading for the facet capsular ligament, which has not been previously defined for such neck injuries. Findings also present a framework for more in-depth methods to define the threshold for persistent pain and could enable extrapolation to the human response.
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Journal of biomechanics · Jan 2006
Clinical TrialChanges in axial stiffness of the trunk as a function of walking speed.
Research suggests that abnormal coordination patterns between the thorax and pelvis in the transverse plane observed in patients with Parkinson's disease and the elderly might be due to alteration in axial trunk stiffness. The purpose of this study was to develop a tool to estimate axial trunk stiffness during walking and to investigate its functional role. Fourteen healthy young subjects participated in this study. ⋯ Estimated axial trunk stiffness increased with increasing walking speed. Functionally, the suppression of axial rotation of thorax may have a positive influence on head stability as well as allowing recoil between trunk segments. Furthermore, the increased stiffness at increased walking speed would facilitate the higher frequency rotation of the trunk in the transverse plane required at the higher walking speeds.
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Journal of biomechanics · Jan 2006
An approach to the simulation of fluid-structure interaction in the aortic valve.
A pair of finite element models has been employed to study the interaction of blood flow with the operation of the aortic valve. A three-dimensional model of the left ventricle with applied wall displacements has been used to generate data for the spatially and time-varying blood velocity profile across the aortic aperture. These data have been used as the inlet loading conditions in a three-dimensional model of the aortic valve and its surrounding structures. ⋯ The aortic valve behaves in an essentially symmetric way under the action of this flow, so that the pressure difference across the leaflets is approximately uniform. This work supports the use of spatially uniform but temporally variable pressure distributions across the leaflets in dry or structural models of aortic valves. The study is a major advance through its use of truly three-dimensional geometry, spatially non-uniform loading conditions for the valve leaflets and the successful modelling of progressive contact of the leaflets in a fluid environment.