Biomedical subjects
Publications and source records attributed to A Huson.
This article describes the function of the tarsal complex as a constrained mechanism. The relationship between the interdependence of the motions of the tarsal joints and the special nature of tarsal joint function is explained, with emphasis on the midtarsal joint and its presumed two axes of motion.
A finite element (FE) model of blood perfused biological tissue has been developed. Blood perfusion is described by fluid flow through a series of 5 intercommunicating vascular compartments that are embedded in the tissue. Each compartment is characterized by a blood flow permeability tensor, blood volume fraction and vessel compliance. Local non-linear relationships between intra-extra vascular pressure difference and blood volume fraction, and between blood volume fraction and the permeability tensor, are included in the FE model. To test the implementation of these non-linear relations, FE results of blood perfusion in a piece of tissue that is subject to increased intramuscular pressure, are compared to results that are calculated with a lumped parameter (LP) model of blood perfusion. FE simulation of blood flow through a contracting rat calf muscle is performed. The FE model used in this simulation contains a transversely isotropic, non-linearly elastic description of deforming muscle tissue, in which local contraction stress is prescribed as a function of time. FE results of muscle tension, total arterial inflow and total venous outflow of the muscle during contraction, correspond to experimental results of an isometrically and tetanically contracting rat calf muscle.
One of the basic aims in the rehabilitation of thoracic spinal cord injured (SCI) patients concerns the regaining of sitting posture control. This implies the development of new postural strategies requiring the adjustment of motor programming processes. The aim of this study was to investigate the time course of postural reorganization during active, clinical rehabilitation of thoracic SCI patients with different SCI levels. Thus changes in motor programming in sitting balance control were investigated in two groups of complete low or high thoracic SCI patients. At several stages during the rehabilitation process an experiment was held in which sitting posture was perturbed systematically using submaximal reaching movements over four reaching distances. This bimanual reaching task was presented as a visual precue choice reaction time (RT) task in which reaching distance (i.e. grade of postural perturbation) was precued. Results indicated that in both high and low thoracic SCI patients RTs in movements involving postural perturbation became shorter during the course of the rehabilitation period. However, low thoracic SCI patients were generally slower in the programming of balance perturbing movements than high thoracic SCI patients, a phenomenon that did not change over time. Furthermore, initial differences in RTs as a function of grade of postural perturbation disappeared in both groups in the course of the rehabilitation phase. Precue benefit, equally large for both groups, did not change as a function of rehabilitation time. It is concluded that the observed phenomena signify the gradual development of new central postural control processes in both SCI groups during rehabilitation. Low thoracic SCI patients, having more residual sensorimotor functions, seem to adopt more complex strategies in maintaining and restoring sitting balance that take longer to specify and to programme. High thoracic SCI patients seem to rely on simpler strategies using more passive postural support.
STUDY DESIGN: This report examines the permeability coefficient and aggregate modulus of slices of anulus cut from canine lumbar intervertebral discs. OBJECTIVES: To examine the influence of radial position on the properties of these materials, including outer samples with intact anulus edge. SUMMARY OF BACKGROUND DATA: The outer edge of anulus fibrosus shows radial bulge during axial compression of motion segments. The radial bulge increases monotonically when the axial compression is sustained for several hours, until a plateau is reached. Triphasic modeling of axial compression shows that this time course of radial bulge can not be obtained using a uniform permeability coefficient according to values in the literature. METHODS: Confined consolidation experiments (controlled load) were designed to measure the time course of uniaxial deformation of samples of anulus that were 4 mm in diameter and 1 mm tall. The rotation symmetry axis of the samples was defined in the radial direction of the disc. The radial permeability coefficient and the aggregate modulus were determined using the consolidation data and the linear biphasic theory. RESULTS: The permeability coefficient was lower at the periphery than in deeper layers of the anulus. Outer samples with outer surfaces that were 0.0-0.5 mm from the anulus edge had an average permeability coefficient of (1.02 +/- 0.57) x 10(-16) m4/Ns (n = 24). Inner samples that were 2.0-2.5 mm from the anulus edge had an average permeability coefficient of (2.81 +/- 0.98) x 10(-16) m4/Ns (n = 13). The aggregate modulus HA of outer samples was significantly higher (HA = 1.56 +/- 0.34 MPa) than that of inner samples (HA = 1.31 +/- 0.47 MPa). CONCLUSIONS: The fact that the outer anulus is less permeable than the inner anulus may explain why radial bulge of anulus fibrosus increases monotonically in time to an equilibrium value during sustained axial compression of a motion segment.
A variety of physical characteristics of athletes has been proposed to be related to the risk to sustain a sports injury. The aim of the present study was to determine the influence of flexibility, anthropometric characteristics and malalignment of the lower extremities on the risk to sustain a sports injury, using a prospective study design and subjects exposed to rather equal extrinsic risk factors. Physical education students (N = 136) were followed during their four-year education. Sixteen flexibility indices, four anthropometric characteristics and five malalignment indices of the lower extremities were assessed at the start of the study and all sports injuries sustained in that four-year period were recorded. No influence of flexibility or anthropometric variables on the total number of injuries or the number of several specific injuries (ankle sprain, muscle rupture, dislocation, shin splints, backache) could be established. Malalignments of the lower extremities (average prevalence 18% and only minor deviations) did show some but inconsistent relations with the number of (specific) injuries. For pelvic obliquity it was positive as predicted, but for malalignment of the rearfoot and a deviant footprint it appeared to be negative. Leg length inequality and malalignment of the knees were not related to injuries. The most likely explanation for these (poor) findings is the relatively low number and great variety of sports injuries recorded. Further, the homogeneity in physical characteristics of the population under study makes it difficult to find significant relationships. A study design that meets both the criterium of similar extrinsic risk factors and that of a wide range of physical characteristics in a representative sporting population, however, is not practicable.
Mechanical interaction between tissue stress and blood perfusion in skeletal muscles plays an important role in blood flow impediment during sustained contraction. The exact mechanism of this interaction is not clear, and experimental investigation of this mechanism is difficult. We developed a finite-element model of the mechanical behavior of blood-perfused muscle tissue, which accounts for mechanical blood-tissue interaction in maximally vasodilated vasculature. Verification of the model was performed by comparing finite-element results of blood pressure and flow with experimental measurements in a muscle that is subject to well-controlled mechanical loading conditions. In addition, we performed simulations of blood perfusion during tetanic, isometric contraction and maximal vasodilation in a simplified, two-dimensional finite-element model of a rat calf muscle. A vascular waterfall in the venous compartment was identified as the main cause for blood flow impediment both in the experiment and in the finite-element simulations. The validated finite-element model offers possibilities for detailed analysis of blood perfusion in three-dimensional muscle models under complicated loading conditions.
A two-dimensional model of the normal foot skeleton, which includes cartilages and ligaments, is used in this analysis of stresses during three quasi-static walking phases: heel-strike, mid-stance and push-off. It is found that in all the walking phases the maximum values of principal stresses occur in the dorsal anterior region of the talus, whereas the highest stress occurs in the push-off phase. The model is used for the simulation of muscle paralysis and its effect on the distribution of principal stresses. Subsequently, the model is used to analyse stresses in the deformed feet of three leprosy patients with complete paralysis of certain muscles. The results demonstrate that both the shape of the foot and the type of muscle paralysis contribute to the development of high stresses in different regions of the foot. These high stresses in regions with reduced mechanical strength could be one of the important factors in the process of tarsal disintegration in leprosy.
Deformation of the surface of passive medial gastrocnemius muscle (MG) was measured in vivo while performing a hysteresis test. The gastrocnemius muscle of male rats were dissected free and the distal tendon was cut. The lateral head was separated from the medial head. The muscle origins were left intact. 60-70 fluorescent, polystyrene spheres (diameter 0.7 mm) were attached to the surface of the MG. During the experiment, two-dimensional video recordings of the movements of the MG were made. The coordinates of the marker centroids were obtained by computer processing of digitized images and marker displacements as a function of time were calculated. Green-Lagrange strains in two principal directions were calculated (epsilon 1, epsilon 2) for three specimens. epsilon 1 had approximately the same direction as the muscle fibers. The longitudinal strain of the fibers (20-30%) was larger than the strain of the aponeurosis (1-5%); p < 0.001. No significant difference was found between the values of the transverse strains of muscle fibers and aponeurosis; the value of epsilon 2 was -6 to -9% for both tissue structures.
A finite element description of blood perfusion has been developed, and is applied to skeletal muscles. Three-dimensional distributions of blood pressures and flows in deforming muscles are calculated. The muscle tissue is considered as a fluid-saturated porous solid. The blood is modeled as a series of five intercommunicating compartmental fluids, representing arterial, arteriolar, capillary, venular and venous blood, that reside in the pores (blood vessels) of the muscle tissue. The blood vessels are modeled as distensible tubes, embedded in the muscle tissue. A 3-D finite element mesh has been mapped on a reconstructed geometry of a gastrocnemius medialis muscle of the rat. Blood perfused linear elastic muscle material behaviour has been assigned to this mesh. A simulation of blood perfusion, resulting from a constant arterio-venous pressure difference, through the reconstructed muscle has been performed. Calculated blood pressure and flow distributions were within physiological range.
In order to simulate blood flow in skeletal muscle, our group has developed a finite element description of perfused skeletal muscle. This model requires input parameters concerning the vascular system, muscle contraction and the geometry of a muscle, including its aponeuroses. The objective of the present paper is to create a geometrical reconstruction of the rat gastrocnemius medialis muscle that can be incorporated in the finite element model. Since this muscle is connected to the plantaris and the gastrocnemius lateralis muscle, a detailed computer graphical reconstruction of the triceps surae muscle, based on histological cross-sections, has been accomplished first. Using this reconstruction, relevant sections were selected to create the finite element mesh of the gastrocnemius medialis muscle. Special attention was payed to the location of the aponeuroses. The mesh can be used in finite element simulations of perfused skeletal muscle.
The aim of this study is to find basic quantitative geometric data that may contribute to the understanding of the etiology of hallux valgus. Embalmed specimens with existing hallux valgus (N = 39) were dissected; 28 variables were measured with a Vernier caliper gauge and toe goniometer. Correlations between pairs of independent variables were calculated. Linear dependency of the hallux angle, varus angle, and the width of the forefoot on a number of independent variables was analyzed by multiple linear regression. A least squares method and a stepwise procedure were used. The distance from the tendon of the flexor hallucis longus muscle to the head of the first metatarsal bone explains more than other variables the variation in hallux angle and width of the forefoot. A widened forefoot is significantly correlated with both hallux and varus angles. The interrelation of the predictor parameters illustrates the complicated hallux valgus phenomenon.
OBJECTIVE: To assess the differences in daily physical activity between children with spastic diplegia and healthy schoolchildren, to determine whether special physical activity programs are needed in the population with cerebral palsy. DESIGN: Cross-sectional design. SETTING: Children's rehabilitation center Franciscusoord (day care center) and elementary schools. SUBJECTS: Children with spastic diplegia (5 boys; mean (+/- SD) age 8.0 +/- 1.4 years; 9 ambulant, 1 wheelchair use) and healthy children (5 boys; mean (+/- SD) age 8.4 +/- 1.0 years). MEASUREMENTS: Total daily energy expenditure (TEE) and sleeping metabolic rate (SMR) were measured by the doubly labeled water technique and a respiration chamber. The TEE/SMR ratio was used as an index for the level of daily physical activity. RESULTS: The TEE/SMR ratio under normal daily conditions in the children with cerebral palsy (mean +/- SD): 1.56 +/- 0.19) was significantly lower (p < 0.05) than in their healthy peers (mean +/- SD: 1.83 +/- 0.23) and was similar to the TEE/SMR ratio in a room-sized chamber. CONCLUSION: Children with spastic diplegia are considerably less active than their healthy peers. We recommend special physical activity programs for these children.
Uniaxial confined compression and swelling experiments on cylindrical specimens taken either in an axial or in a radial direction from a canine lumbar annulus fibrosus are presented. The loading protocol consisted of a combination of stepwise mechanical and chemical loading. Swelling and consolidation curves of normalized displacement versus square root of normalized time did not show a dependence on site or orientation of the specimen. All stages in which height increases, namely, conditioning, swelling, and desolidation show only slight differences in these normalized curves. Consolidation is initially faster, and later slower. The transport coefficient for axial specimens is higher than for radial specimens, for consolidation e.g., 3.14 +/- 1.56 10(-10) m2s(-1) and 1.11 +/- 0.33 10(-10) m2s(-1) respectively, the biphasic aggregate moduli are 1.01 +/- 0.31 MPa and 0.66 +/- 0.30 MPa, respectively.
The goal of this study was to investigate whether ocular and hand motor systems operate independently or whether they share processes. Using dual-task methodology, reaction time (RT) latencies of saccadic eye and hand motor responses were measured. In experiment 1, the hand and eye motor systems produced rapid, aimed pointing movements to a visual target, which could occur either to the left or right of a central fixation point. Results showed that RT latencies of the eye response were slower in the dual-task condition than in the single-task condition, whereas the RT latencies of the hand response were virtually the same in both conditions. This interference effect indicated that the ocular and manual motor systems are not operating independently when initiating saccadic eye and goal-directed hand movements. Experiment 2 employed the same experimental paradigm as experiment 1, except for one important modification. Instead of a goal-directed hand movement to the target stimulus, subjects had to make a button-press response with either the index or middle finger of the right hand dependent upon whether the stimulus occurred to the right or left of the control fixation point. The aim of experiment 2 was to investigate the issue whether the observed interference effect in experiment 1 was specific or non-specific (e.g. overhead costs due to coordinating any two responses). The finding that saccadic eye movements and button-press responses in the dual-task condition could be initiated without delay relative to the single-task conditions, supports the specific interference interpretation.
Characteristics results of postmortem experiments on five knee-joint specimens are reported. The experiments were performed to investigate the applicability of a local linearization technique that would make it possible to describe the dynamic behavior of the joint in terms of transfer functions. The results indicate that the stiffness of the bracing wires, attached to muscle tendons to create a static equilibrium position, can be accounted for when determining the stiffness of the joint. Besides the static equilibrium configuration, the magnitude of the dynamic load and the type of dynamic load applied to the joint can be shown to have their influence. As the influence of the dynamic load is significant, it has to be concluded that in essence the knee joint has to be regarded as a nonlinear system, making application of a Local Linearization Technique questionable. However, when the magnitude of the dynamic load is included as an additional measurement parameter, an indication can be obtained about the behavior of the joint and the degree of nonlinearity.
A description is given of the results obtained for step excitation for two human knee joint specimens using a time-domain analysis technique. As was expected from the results of a previous study, the magnitude of the dynamic load applied has a marked influence upon the stiffness and damping values for the two observed vibration modes. Deliberate damaging of selected joint elements also yields a well observable change in the dynamic behavior of the joint although these changes are difficult to interpret. Here the use of a nonlinear dynamic numerical model of the knee joint seems indispensable. An important observation is, however, that the experimental method discussed here enables to quantify the behavior of the joint and therefore may provide a valuable tool for validation of such a model.
An axisymmetric finite element model is formulated which comprises a rigid spherical indentor, a meniscal ring and an articular cartilage layer, both considered as mixture materials which are interacting with an ideal fluid sub-system. From parameter studies it is concluded that the application of the mixture theory in comparison with solid modelling only leads to significant effects when the outer surfaces of the components are not sealed. The load distribution appears to change enormously during relaxation of the models. Initially the largest fraction of the load is borne by the fluid in the cavity, while at the end, when the system has reached its final configuration, the meniscal ring bears the major part of the load. Further, the length of the relaxation period appears to depend on the magnitude of the step change of the load. Finally, the curvature of the spherical indentor appears to have significant effects on the loading of the meniscal ring, only immediately after the step changes of load are applied, and these effects disappear as soon as the fluid starts to exude from the models.
Muscle fibre lengths, pennation angles, and sarcomere lengths were measured (the latter by a diffraction technique) for each of the muscles of three embalmed lower-leg specimens. From these data and filament lengths from Walker & Schrodt (1973), the optimum fibre lengths were determined. Relationships between length and active force (at full activation) of the lower-leg muscles were calculated by use of (i) a unipennate muscle model, (ii) a bipennate model, and (iii) bipennate models in which the cosine of the pennation angle is approximated as length independent. It is concluded that the first two models are equally useful and that the use of the last models is discouraged in case of strongly pennated muscles. Non-uniformity of fibre parameters within one muscle appears to have little effect on the force-length relationship.