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RESEARCH PAPERS

J Biomech Eng. 1983;105(3):201-209. doi:10.1115/1.3138407.

A numerical simulation was devised to determine ligament strains, facet face interaction, and disk fiber strain in the lumbar intervertebral joint under load. This technique uses experimentally derived load deflection and morphologic data from lumbar cadaver specimens from which initial and displaced soft tissue attachment points can be calculated. This allows the strain data to be derived. The effect of disk bulge is also considered. The calculated strains of most ligaments except the facet capsular ligaments were found to be insensitive to anatomical measurement variability of ± 1 mm.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(3):210-215. doi:10.1115/1.3138408.

A numerical simulation of soft-tissue strain and facet face interaction in the lumbar intervertebral joint under load was performed. The results, compared with a previous experimental sectioning study, showed that disk fiber strain was the main mechanism in shear resistance, except posterior shear, where the facets were main load bearing members. In axial compression, compression of the annulus was found, with a significant decrease in compressive strain resulting from annulus bulging, but no contact was found in the facet joints. The posterior ligaments, except for the facet capsules and ligamentum flavum, were found to be active only in flexion and lateral bending, while the facets and the disk both played major roles in resisting axial torsion moments.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(3):216-225. doi:10.1115/1.3138409.

In this first part of a two-part paper, the results of measurement of static pressure distribution on the tibial surface of the knee are presented. Results with intact menisci have been obtained from 18 specimens. Eight of these specimens were the subject of further measurements following medial meniscectomy. The study has been carried out at various flexion angles of the knee with the joint subjected to a compressive force, with or without an initial passive relative displacement between the joint members. The results indicate that a significant fraction of the joint compressive load is transmitted through the menisci and that total meniscectomy causes a drastic alteration in the pressure distribution on the tibial surface. Clinical implications of these results, in terms of post-meniscectomy degenerative changes and mechanism of meniscal lesions, have been discussed.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(3):226-236. doi:10.1115/1.3138410.

This second part of a two-part paper is concerned with the measurement of static pressure distribution on the retropatellar surface. The study has been performed in a loading apparatus designed to simulate individually the lines of action and the magnitudes of the tensions in the components of the quadriceps femoris muscle group. Results have been obtained using 24 specimens in the knee flexion range 0 to 130 deg and employing a net quadriceps tension of 734 N. Particular emphasis has been placed on the evaluation of the sensitivity of the results to variations in the characteristics of the simulated quadriceps tension. The pressure distribution results have been interpreted in terms of variation of the normal force and the average contact stress on the retropatellar surface as a function of flexion angle. It has been shown that the “pulley” model of the patella consistently overestimates the actual patellofemoral joint reaction force throughout the range of flexion. Clinical implications of the results, in terms of etiology of degeneration of patellar cartilage, have been discussed.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(3):237-243. doi:10.1115/1.3138411.

A new technique for solving the combined state and parameter estimation problem in thermographic tomography is presented. The technique involves the direct substitution of known skin temperatures into the finite difference form of the bio-heat transfer equation as formulated for solving an initial value problem with a convection boundary condition at the skin surface. These equations are then used to solve the inverse bio-heat transfer problem for the unknown subcutaneous tissue temperatures and physiological parameters. For a small number of nodal points, closed form algebraic solutions are obtained. For larger sets of equations, a hybrid technique is used in which the problem is initially posed as an unconstrained optimization problem in which the model equation error is minimized using the conjugate gradient descent technique to get close to a solution. Then a generalized Newton-Raphson technique was used to solve the equations. A numerical simulation of a one-dimensional problem is investigated both with and without noise superimposed on the input (transient) skin temperature data. The results show that the technique gives very accurate results if the skin temperature data contains little noise. It is also shown that if the physical properties of the tissue and the metabolism are known, that a given set of proper transient skin temperature inputs yields a unique solution for the unknown internal temperatures and blood perfusion rates. However, the similar problem with known blood perfusion rates and unknown metabolisms does not yield a unique solution for the internal temperatures and metabolisms.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(3):244-248. doi:10.1115/1.3138412.

When attempting to evaluate the mechanical properties of human bones in vivo by mechanical vibration analysis, some essential requirements must be met. A quantitative relation between measured vibration parameters (e.g., natural frequency) and mechanical bone properties must be available, in-vivo vibration modes should correctly be identified and the associated natural frequencies reproducibly and accurately measured, the influence of joints and soft tissues must be known. These problems were addressed by modal analysis (i.e., experimental determination of natural frequencies, mode shapes and damping ratios) of human tibiae in the following situations: 1) dry excised tibiae, 2) fresh excised tibiae, 3) in-vivo tibiae, 4) tibiae in an amputated leg, in different steps of dissection. In the in-vivo measuring conditions used by the authors, the tibia vibration is practically free-free. Two single bending modes (at ± 270 Hz and ± 340 Hz, respectively), each of them corresponding with one principal direction for bending, were identified. The difference between the natural frequencies observed in vivo and those of fresh excised tibiae is almost completely caused by the effect of muscles (added mass and damping), whereas joints and skin play only a minor role. Frequency differences between fresh and dry excised tibiae are largely accounted for by the absence of bone marrow in the latter.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(3):249-257. doi:10.1115/1.3138413.

Mathematical models for 1) musculoskeletal dynamics, and 2) reflex feedback, based on the results of the authors’ frequeny-response measurements on normal adult male human subjects, are combined to produce a model for physiological tremor in such subjects. An analysis of this model shows that the system will be unstable to small disturbances (that is, tremor will occur) under certain conditions of external loading. Further, when the system is unstable, nonlinearities in the model produce responses in the form of limit cycles, and both the frequency and amplitude of the resulting tremor can be calculated. For constant loads applied through a constant compliance, the model predicts the onset of tremor at low loads, a maximum intensity of tremor at loads corresponding to 30–50 percent of maximum voluntary effort, and a decrease in the tremor amplitude at still higher loads.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(3):258-262. doi:10.1115/1.3138415.

In-vitro, steady flow in a casting of the profunda femoris branch of the femoral artery of man was studied by measuring pressure differences in the main lumen and also in the branch over a large Reynolds number range from 200 to 1600. Effects of viscous and inviscid flows in this femoral artery branch were demonstrated quantitatively. The critical ratio of the flow rate in the branch to the upstream main lumen, ṁ 3 /ṁ 1 , in this casting was found to be 0.4, above which the inviscid flow analysis indicated a pressure rise and below which it yielded a pressure drop in the main lumen across the branch junction. Pressure rises were experimentally found to occur both in the main lumen and in the branch for certain ranges of ṁ 3 /ṁ 1 .

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(3):263-267. doi:10.1115/1.3138416.

A numerical model is developed to predict the complex velocity, shear and pressure fields in steady turbulent flow through a disk-type prosthetic heart valve in a constant diameter chamber. The governing Navier-Stokes equations are reduced to a set of simultaneous algebraic finite-difference equations which are solved by a fast-converging line-iterations technique. A two-parameter, two-equation model is employed to determine the turbulent viscosity. Numerical results are obtained for stream function, vorticity, and shear and normal stresses. The regions of very high shear and normal stresses in the fluid and at the walls are identified. The maximum value of the shear stress occurring near the upstream corner of the disk may cause hemolysis. The technique can be used together with in-vitro physcial experiments to evaluate existing or future prosthetic heart valve designs.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(3):268-274. doi:10.1115/1.3138417.

A three-dimensional stress-strain relationship derived from a strain energy function of the exponential form is proposed for the arterial wall. The material constants are identified from experimental data on rabbit arteries subjected to inflation and longitudinal stretch in the physiological range. The objectives are: 1) to show that such a procedure is feasible and practical, and 2) to call attention to the very large variations in stresses and strains across the vessel wall under the assumptions that the tissue is incompressible and stress-free when all external load is removed.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(3):275-282. doi:10.1115/1.3138418.

The impedance (pressure drop/flow rate) of four curved artery models has been determined experimentally for steady and periodic flows simulating conditions in the aortic arch. Steady flow results indicate that very short entry lengths are required for flow development in curved artery models, and impedance is elevated above straight tube values by a factor of 3–4 for mean flow conditions in the aortic arch. Results for periodic flow with a nonzero mean show a significant elevation of mean flow impedance relative to values for steady flow at the mean flow rate—a factor of 2–3 for aortic arch flow conditions. The impedance of the first harmonic of periodic flows follows straight tube theory at high values of the unsteadiness parameter in agreement with available theory for curved tubes. The implications of the impedance measurements for wall shear stress in the aortic arch are discussed.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(3):283-289. doi:10.1115/1.3138419.

A theoretical formulation for studying limb motions and joint kinetics by multiaxial accelerometry is developed. The technique is designed to study the swing phase of human gait, modeling the lower leg as a rigid body. Major advantages of the approach are that acceleration information needed for the calculation of forces and moments is generated directly, and that the method automatically generates its own initial conditions. Results of validation experiments using both artificial and experimental data demonstrate that the method is theoretically valid, but that it taxes available instrumentation and requires further development before it can be applied in a clinical setting.

Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(3):294-295. doi:10.1115/1.3138421.

Fibers cannot carry compression, and reinforcing fibers in a cylinder can only carry load if they are kept taut by the deformations of the cylinder. In the present study it is found that in pure bending, deformations that change the pitch, i.e., the angle between the fibers and the cross-sectional plane, towards 30 deg will slacken the fibers. With an initial pitch different than 30 deg, fibers in one half of the cross section will then be slackened by bending, and this half of the cylinder becomes unstable. Applied to the mechanics of the intervertebral disks, this may help explain mechanisms leading to nucleus prolaps.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(3):296-299. doi:10.1115/1.3138422.

Sensitivity of tensile strength, failure strain, and failure energy density to strain rate was studied for rat-tail tendon (RTT), a collagen-rich connective tissue. Tendons from animals aged 1–27 months were stretched at a high (720 percent/s) and low (3.6 percent/s) strain rate. Each failure parameter increased with strain rate. However, the sensitivity of tendon failure to rate of strain decreased rapidly during growth and sexual maturation of the animal. The study provides basic data on the rate-sensitive strength of collagen fibers using RTT.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(3):300-307. doi:10.1115/1.3138423.

The burn process resulting from the application of a hot, cylindrical source to the skin surface was modeled using the finite element technique. A rotationally symmetric 125-element mesh was defined within the tissue beneath and outlying to an applied heating disk. The disk temperature and duration of contact were varied, respectively, between 50 and 100°C for up to 30 s. Natural convection with ambient air was assumed for areas of skin surface not in direct contact with the disk. The simulated thermal history was used in a damage integral model to calculate the extent and severity of injury in the radial and axial dimensions.

Commentary by Dr. Valentin Fuster

REPORTS

J Biomech Eng. 1983;105(3):257. doi:10.1115/1.3138414.
FREE TO VIEW
Abstract
Topics: Biomechanics , China
Commentary by Dr. Valentin Fuster

TECHNICAL BRIEFS

J Biomech Eng. 1983;105(3):308-309. doi:10.1115/1.3138424.
Abstract
Topics: Elastic moduli
Commentary by Dr. Valentin Fuster
J Biomech Eng. 1983;105(3):309-314. doi:10.1115/1.3138425.

The basic features and the performance characteristics of a transducer to measure in-vitro static pressure distribution at the articular interfaces of intact synovial joints are described. Pressure distribution is interpreted from the microindentation pattern left on a thin plastic material, the indenter and the plastic material having been subjected to load between the articular surfaces. The effects of the finite thickness and compliance of the transducer and the effects of the time-dependent response properties of the articular cartilage on the accuracy of measurement have been estimated by means of specific experiments and analyses.

Commentary by Dr. Valentin Fuster

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