J Biomech Eng. 1989;111(2):97-106. doi:10.1115/1.3168361.

The goal of this in vitro study was to investigate the initial postoperative mechanical state of the knee with various types of anterior cruciate ligament (ACL) reconstructions. An experimental knee testing system was developed for the in vitro measurement of ligament forces and three-dimensional joint motion as external loads were applied to fresh knee specimens. Two groups of knee specimens were tested. In test series #1, two intraarticular reconstructions were performed in each of five specimens using semifree and free patellar tendon grafts with bone blocks. In test series #2, a more carefully controlled intraarticular reconstruction was performed in five specimens using a semifree composite graft consisting of the semitendinosus and gracilis tendons augmented with the Ligament Augmentation Device. Ligament force and joint motion data were collected as anteriorly directed tibial loads were applied to the normal joint, the joint with a cut ACL and the reconstructed joint. These knee joint states were compared on the basis of ACL or graft forces, joint motion and load sharing by the collateral ligaments. The dominate result of the study was that the forces and motions defining the mechanical state of the knee after the ACL reconstructions in both test series were highly variable and abnormal when compared to the normal knee state. The higher level of surgical control series #2 did not decrease this variability. There was a poor correlation between motion of the reconstructed knee relative to normal, and the ACL graft force. There was little consistent difference in force and motion results between the surgical procedures tested.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1989;111(2):107-112. doi:10.1115/1.3168351.

Modelling of the human shoulder complex is essential for the multi-segmented mathematical models as well as design of the shoulder mechanism of anthropometric dummies. In Part I of this paper a three-dimensional kinematic model is proposed by utilizing the concepts of kinematic links, joints, and joint sinuses. By assigning appropriate coordinate systems, parameters required for complete quantitative description of the proposed model are identified. The statistical in-vivo data base established by Engin and Chen (1986) is cast in a form compatible with the model by obtaining a set of unit vectors describing circumductory motion of the upper arm in a torso-fixed coordinate system. This set of unit vectors is then employed in determining the parameters of a composite shoulder complex sinus of a simplified version of the proposed model. Two methods, namely the flexible tolerance and the direct methods, are formulated and tested for the determination of an elliptical cone surface for a given set of generating unit vectors. Numerical results are presented for the apex angles and orientation of the composite joint sinus cone with respect to the anatomical directions.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1989;111(2):113-121. doi:10.1115/1.3118775.

In this paper, individual joint sinus cones associated with the sternoclavicular, claviscapular, and glenohumeral joints of the three-dimensional kinematic model introduced in Part I for the human shoulder complex are quantitatively determined. First, mathematical description of the humerus orientation with respect to torso is given in terms of eight joint variables. Since the system is a kinematically redundant one, solution for the joint variables satisfying a prescribed humerus orientation is possible only if additional requirements are imposed; and the “minimum joint motion” criterion is introduced for this purpose. Two methods, namely the Lagrange multipliers and flexible tolerance methods, are formulated and tested for the optimization problem. The statistical in-vivo data base for the circumductory motion of the upper arm is employed to determine a set of joint variables via optimization, which are then utilized to establish the sizes and orientations of the elliptical cones for the individual joint sinuses. The results are discussed and compared with those given on the basis of measurements made on cadaveric specimens.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1989;111(2):122-127. doi:10.1115/1.3168352.

Based on an idealized model of a homogeneous, isotropic beam-column, the second stiffest axis under static loading was derived. The maximum allowable force for the second stiffest axis was then examined. The ratio of the maximum allowable forces of the second stiffest axis to the stiffest axis was established. The stiffness ratio of the second stiffest axis to the stiffest axis was also found. Taking buckling into consideration, the safe load region for all possible acting directions was derived. The implications of the idealized model for cervical spine trauma are discussed.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1989;111(2):128-135. doi:10.1115/1.3168353.

The viscous criterion is a recently developed criterion to assess injury severity of the human thorax. In the viscous criterion, the peak viscous response, which is defined as the maximum product of deformation velocity and compression of an object, is proposed as a predictor of injury risk. However, the physical meaning of the criterion is not very clear. In this paper, the mathematical properties of the viscous criterion are analyzed. A mechanical thorax model is then used to relate the criterion to the physical quantities of the model using energy concepts. It is found that the so-called peak viscous response is strongly related to the peak energy storing rate of the thorax which is not related to the viscosity of the thorax. It is also shown that the viscous response of the thorax is given by the integral of the velocity squared with respect to time. The analysis is further expanded to a more general case to result in four criteria based upon the energy concepts. A hypothesis for injury assessment is proposed by using the four criteria.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1989;111(2):136-140. doi:10.1115/1.3168354.

The tensile strength of skin is associated, in part, with its potential for laceration from impact. The quasi-static tensile strength of skin depends on orientation. The objective of this study was to determine whether the strength of skin in high speed tensile failure experiments exhibits a similar dependence on orientation. Tensile experiments were conducted at 6000 percent/s and 30 percent/s on dorsal skin of rats aged 1–6 months. Experiments were performed on specimens cut perpendicularly and longitudinally to the spine at cranial and caudal locations. The tensile failure properties depended on location, orientation, age and strain rate. The strength was dependent on orientation to the same degree in high and low speed tests. This helps explain why accident statistics show that skin lacerates preferentially on the body.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1989;111(2):141-146. doi:10.1115/1.3168355.

A nonlinear differential equation describing the Doppler velocity profile for blood flow through the mitral valve has been derived. This equation is based on fluid dynamics and a simple, but comprehensive model of atrial and ventricular mechanics. A numerical solution to the equation is described and provides excellent agreement with Doppler velocity curves obtained clinically. One important result of the theory is that in patients with mitral stenosis, the slope of the clinically observed straight-line descent of the velocity profile is proportional to the mitral orifice area and inversely proportional to the atrioventricular compliance.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1989;111(2):147-151. doi:10.1115/1.3168356.

We analyze theoretically the single-file flow of asymmetric red blood cells along cylindrical capillaries. Red cells in narrow capillaries are typically nonaxisymmetric, with the cell membrane moving continuously around the cell. In our analysis, cell shape and streamlines of membrane motion are prescribed. Lubrication theory is used to compute velocities and pressures in the fluid surrounding the cell. Conditions of zero lift, zero torque, zero drag, and energy conservation in the cell are imposed. Predicted tank-treading frequency, cell inclination and transverse displacement are small. Cell asymmetry and tank-treading are found to have little effect on the apparent viscosity of blood in capillaries with diameters up to 7 μm.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1989;111(2):152-156. doi:10.1115/1.3168357.

New data on laminar heat convection with red cell suspensions have been gathered for both heating and cooling. When compared to data for the suspending medium alone, it is apparent that the red cells enhance laminar heat transfer when Pe > 4. This is probably due to particle movements. These new data disagree with earlier studies which indicated no enhancement of heat transfer for blood cell suspensions. The data do agree with previous correlations for enhanced thermal transport in sheared suspensions.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1989;111(2):157-165. doi:10.1115/1.3168358.

Peristaltic pumping by a sinusoidal traveling wave in the walls of a two-dimensional channel filled with a viscous incompressible fluid in which are distributed identical rigid spherical particles, is investigated theoretically. A perturbation solution is obtained which satisfies the momentum equations for the case in which amplitude ratio (wave amplitude/channel half width) is small. The results show that the fluid phase mean axial velocity decreases with increase in the particle concentration. The phenomenon of reflux (the mean flow reversal) is discussed. A reversal of velocity in the neighborhood of the centerline occurs when the pressure gradient is greater than that of the critical reflux condition. It is found that the critical reflux pressure is lower for the particle-fluid suspension than for the particle-free fluid. It is further observed that the mean flow reversal is strongly dependent on the particle concentration and the presence of particles in the fluid favors the reversal flow. A motivation of the present analysis has been the hope that such a theory of two-phase flow process is very useful in understanding the role of peristaltic muscular contraction in transporting bio-fluid behaving like a particle-fluid mixture. Also the theory is important to the engineering applications of pumping solid-fluid mixtures by peristalsis.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1989;111(2):166-172. doi:10.1115/1.3168359.

The bacterium Xanthomonas campestris , which synthesizes the commercially important polysaccharide xanthan, was grown aseptically in 1.2 L fermenters using semicontinuous cell culture technique (d′ = 0.0035 h−1 ). The effects of carbon-substrate concentration on xanthan production were investigated at three initial glucose concentrations (G0 = 15, 20, 25 g/L). Cell biomass synthesis was nitrogen-limited by use of a chemically defined medium that contained NH3 -N as the sole nitrogen source at a concentration where it was exhausted before glucose. A linear relationship between biomass synthesis and NH3 -N depletion was observed. This relationship remained valid only until NH3 -N exhaustion, after which biomass concentration slowly rose another 20 percent before declining. Another linear relationship was found between xanthan synthesis and glucose uptake. This relationship was unaffected by the disappearance of NH3 -N and held through glucose exhaustion. The quasi-stoichiometric yield coefficients obtained for each linear relationship were not affected by G0 . Biomass synthesis kinetics showed no variation with G0 before NH3 -N exhaustion; afterwards, cell biomass decline was delayed by increasing G0 . Xanthan synthesis kinetics displayed no detectable response to depletion of NH3 -N and plateauing of biomass concentration; however, there was a marked slow down in the net rate of xanthan synthesis and a drop in xanthan yield after cell biomass decline became noticeable.

Commentary by Dr. Valentin Fuster



Commentary by Dr. Valentin Fuster

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