Mehran Kasra

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The pathogenesis of vibration-induced disorders of intervertebral disc at the cellular level is largely unknown. The objective of this study was to establish a method to investigate the ranges of constructive and destructive hydrostatic loading frequencies and amplitudes in preventing or inducing extracellular disc matrix degradation. Using a hydraulic(More)
To improve our understanding of the dynamic characteristics of the human lumbar spine, both experimental and finite-element methods are required. The experimental methods included measurement of the axial steady state response, resonant frequencies, and damping of seven lumbar motion segments under an upper-body mass of 40 kg. The influence of the presence(More)
The pathogenesis of vibration-induced disorders of intervertebral disc at the cellular level is largely unknown. Dynamic loads with frequencies close to that of the in vivo human spine resonant frequency (4-6 Hz) have a destructive effect, which may induce extracellular disc matrix (ECM) degradation. To investigate this issue, three-dimensional (3D)(More)
Reliable computation of spinal loads and trunk stability under whole body vibrations with high acceleration contents requires accurate estimation of trunk muscle activities that are often overlooked in existing biodynamic models. A finite element model of the spine that accounts for nonlinear load- and direction-dependent properties of lumbar segments,(More)
Feral adult female cynomolgus monkeys were divided into three groups and treated for two years: (1) normal controls; (2) weak androgenic treatment (androstenedione+estrone); and (3) strong androgenic treatment (testosterone). The tibiae and the trabecular bone of femoral head from each group were tested mechanically. There were no significant changes in the(More)
The purpose of this study was to evaluate the effects of ovariectomy on the mechanical properties of bone in the aged Sprague-Dawley rat model of osteoporosis. Eight female rats were sacrificed at the start of the study, at the age of four months. Twenty-four remaining rats were then bilaterally ovariectomized (OVX), and another twenty-four served as(More)
The purpose of this study was to examine the effects of estrogen replacement, in concert with three different progestin regimens, on the mechanical properties of rat femoral cortical bone. Ninety-two 11-month-old female Sprague-Dawley rats were randomly divided into six groups and were treated for a duration of 6 months. Group-1 rats were intact controls,(More)
Feral adult female cynomolgus monkeys were divided into two groups: normal controls and ovariectomized. Tibiae and trabecular bones from the femoral head, from each group, were tested using a materials testing machine. The bending stiffness of the tibiae was measured by nondestructive three-point bending tests and their maximum torque capacity by(More)
An idealized three-dimensional finite element model of a rodlike trabecular bone structure was developed to study its static and dynamic responses under compressive loading, considering the effects of bone marrow and apparent density. Static analysis of the model predicted hydraulic stiffening of trabecular bone due to the presence of bone marrow. The(More)
The mechanical properties of cortical and trabecular bones from beagles treated with the bisphosphonate pamidronate (administered intermittently 1 week every month for 3 months, at a dosage of 0.45 mumol/kg/day) were assessed. The mechanical properties of cortical bone were measured by four-point bending tests on femoral quadrants, in order to measure their(More)