RESPONSE ANALYSIS OF THE KNEE JOINT IN FLEXION UNDER QUADRCEPS ACTIVATION

The human knee joint is a complex structure with interactions between muscle forces, ligaments, menisci and articulations at different regions. Proper management of rehabilitation and treatment programs requires a solid understanding of such interactions in intact and injured conditions. Towards this goal, a realistic nonlinear 3-D finite element model of the entire knee joint is developed. In this work, the ligament forces and contact stresses/areas are computed as the unconstrained joint is flexed from 0° to 90° ± a constant 137 N quadriceps force. Predictions support the coupling between various components as a function of quadriceps exertion and flexion angle. The model is promising in augmenting our understanding of the joint function leading to improved design for rehabilitation programs and replacement procedures in active patients

KNEE JOINT LIGAMENT RECONSTRUCTION: ON PRETENSION AND COUPLING IN CRUCIATE LIGAMENTS

Wide range of knee cruciate ligament reconstruction procedures with different materials, stiffness, pretensions, orientations, and insertion locations are currently used with the primary goal to restore the joint laxity. With the general lack of success in preservation of force in the reconstructed ligament, the concern, not yet addressed, arises as to the effect of reconstruction on the other intact cruciate ligament. Using a 3-D finite element model, we examined this hypothesis by varying the pretension in each ligament under flexion ±A-P loads and quantifying the extent of coupling between cruciate ligaments. A remarkable coupling was predicted. Moreover, changes in laxity and in ligament forces as ligament pretension was altered varied with flexion and loads. These findings have important consequences in proper management and rehabilitation of the joint ligament disorders

Development of modifying compounds for multilayer nano-structured coatings for cutting tools

The subject of this study was to research and develop modified multilayer nanostructured wear-resistant coatings (NWC) for cutting tools. NWC are formed through the innovation process of filtered cathodic vacuum-arc deposition (FCVAD). The processes of FCVAD allow forming NWCs by filtering vapour-ion flow of macro/micro particles in the plasma torch of vacuum arc, using the plasma duct of special structure isolated from the station chamber, when the angle of rotation of the plasma stream is 120°. This work presents the configuration of the system, alongside with the influence of process parameters on the output. The topology of the coatings is presented together with the hardness and a comparison between standard physical vapour deposition (arc PVD) and FCVAD coating technologies. Machining tests were undertaken in turning of standard HB200 steel and heat resistant nickel alloy. The results are presented in terms of tool flank wear. It is shown that the application of the NWC secured 2-6 fold extended tool lif

Effects of sex, age, body height and body weight on spinal loads: sensitivity analyses in a subject-specific trunk musculoskeletal model.

Subject-specific parameters influence spinal loads and the risk of back disorders but their relative effects are not well understood. The objective of this study is to investigate the effects of changes in age (35-60 years), sex (male, female), body height (BH: 150-190 cm) and body weight (BW: 50-120 kg) on spinal loads in a full factorial simulation using a personalized (spine kinematics, geometry, musculature and passive properties) kinematics driven musculoskeletal trunk finite element model. Segmental weight distribution (magnitude and location along the trunk) was estimated by a novel technique to accurately represent obesity. Five symmetric sagittal loading conditions were considered, and main effect plots and analyses of variance were employed to identify influential parameters. In all 5 tasks simulated, BW (98.9% in compression and 96.1% in shear) had the greatest effect on spinal loads at the L4-L5 and L5-S1 levels followed by sex (0.7% in compression and 2.1% in shear), BH (0.4% in compression and 1.5% in shear) and finally age (<5.4%). At identical BH and BW, spinal loads in females were slightly greater than those in males by ~4.7% in compression and ~8.7% in shear. In tasks with no loads in hands, BW-normalized spinal loads further increased with BW highlighting the exponential increase in spinal loads with BW that indicates the greater risk of back disorders especially in obese individuals. Uneven distribution of weight in obese subjects, with more BW placed at the lower trunk, further (though slightly <7.5%) increased spinal loads.This work was supported by the institut de recherche Robert-Sauvé en santé et en sécurité du travail 294 (IRSST-2014-0009) and the fonds de recherche du Québec en nature et technologies (FRQNT)

Transitions across cognitive states and death among older adults in relation to education: a multi-state survival model using data from six longitudinal studies

Introduction: This study examines the role of educational attainment, an indicator of cognitive reserve, on transitions in later life between cognitive states (normal Mini-Mental State Examination (MMSE), mild MMSE impairment, and severe MMSE impairment) and death. / Methods: Analysis of six international longitudinal studies was performed using a coordinated approach. Multistate survival models were used to estimate the transition patterns via different cognitive states. Life expectancies were estimated. / Results: Across most studies, a higher level of education was associated with a lower risk of transitioning from normal MMSE to mild MMSE impairment but was not associated with other transitions. Those with higher levels of education and socioeconomic status had longer nonimpaired life expectancies. / Discussion: This study highlights the importance of education in later life and that early life experiences can delay later compromised cognitive health. This study also demonstrates the feasibility and benefit in conducting coordinated analysis across multiple studies to validate findings

The effect of quince leaf (Cydonia oblonga miller) decoction on testes in hypercholesterolemic rabbits: A pilot study

Current medical literature lacks any evidence of the protective effects of quince leaf on testes. Therefore, the aim of the present study was to assess the effect of quince (Cydonia oblonga Miller) leaf decoction on testicular injury and impaired spermatogenesis induced by hypercholesterolemia in rabbits. Eleven mature New Zealand white male rabbits were randomly divided into three groups: group 1 (hypercholesterolemia, n=3), group 2 (hypercholesterolemia plus quince treatment, n=6), and group 3 (control, n=2). Groups 1 and 2 received a cholesterol-enriched diet for six weeks. Group 2 received C. oblongaleaf decoction as drinking supplement as well. After six weeks, a normal diet was substituted in groups 1 and 2 for another six weeks. Group 3 (control group) was maintained throughout the study on a regular diet. At the end of the 12th week, the left testes of the animals were resected for light microscopic study with particular attention to the maturity of germ cells in seminiferous tubules using Johnsen’s score. Increase in intertubular connective tissue and diameter of vessels, abundant spermatogonia and primary spermatocytes along the reduced germinal epithelium were noted in all rabbits of the group 1. The remaining animals in groups 2 and 3 had no significant changes in their testicular sections. The mean Johnsen’s score of group 1 (4.20±1.92) was significantly lower than that of group 2 (7.33±0.52) and group 3 (7.05±0.07). (P=0.01). Inconclusion, quince leaf decoction (C. oblonga Miller) protected rabbit testes and spermatogenesis from damage induced by hypercholesterolemia

A model and application of vibratory surface grinding

This paper presents a model of surface grinding with superimposed oscillation of the workpiece. The parameters of the model were experimentally derived and the equations of motions of the system were solved using MATLAB. The results obtained showed a significant decrease in the amplitude of the relative vibration between the wheel and workpiece when the oscillation was superimposed onto the feed motion of the workpiece. A range of experimental work was undertaken and the results showed that the vibratory process had a superior performance in absolute terms with reference to conventional grinding. Low forces along with longer tool life were recorded with the added vibration. A notion of dynamic relief was introduced to express the efficiency of the vibratory process. Copyright © 2018 by ASME

Biomechanical analysis of the lumbar spine on facet joint force and intradiscal pressure - a finite element study

<p>Abstract</p> <p>Background</p> <p>Finite element analysis results will show significant differences if the model used is performed under various material properties, geometries, loading modes or other conditions. This study adopted an FE model, taking into account the possible asymmetry inherently existing in the spine with respect to the sagittal plane, with a more geometrically realistic outline to analyze and compare the biomechanical behaviour of the lumbar spine with regard to the facet force and intradiscal pressure, which are associated with low back pain symptoms and other spinal disorders. Dealing carefully with the contact surfaces of the facet joints at various levels of the lumbar spine can potentially help us further ascertain physiological behaviour concerning the frictional effects of facet joints under separate loadings or the responses to the compressive loads in the discs.</p> <p>Methods</p> <p>A lumbar spine model was constructed from processes including smoothing the bony outline of each scan image, stacking the boundary lines into a smooth surface model, and subsequent further processing in order to conform with the purpose of effective finite element analysis performance. For simplicity, most spinal components were modelled as isotropic and linear materials with the exception of spinal ligaments (bilinear). The contact behaviour of the facet joints and changes of the intradiscal pressure with different postures were analyzed.</p> <p>Results</p> <p>The results revealed that asymmetric responses of the facet joint forces exist in various postures and that such effect is amplified with larger loadings. In axial rotation, the facet joint forces were relatively larger in the contralateral facet joints than in the ipsilateral ones at the same level. Although the effect of the preloads on facet joint forces was not apparent, intradiscal pressure did increase with preload, and its magnitude increased more markedly in flexion than in extension and axial rotation.</p> <p>Conclusions</p> <p>Disc pressures showed a significant increase with preload and changed more noticeably in flexion than in extension or in axial rotation. Compared with the applied preloads, the postures played a more important role, especially in axial rotation; the facet joint forces were increased in the contralateral facet joints as compared to the ipsilateral ones at the same level of the lumbar spine.</p