D. Geiger

Fourier analysis of trunk displacements: a method to identify the lame limb in trotting horses

The aim of this paper is to present a method allowing the identification of the lame limb in trotting horses. Using a 3-D kinematic analysis system, 13 sound and 25 lame horses fitted with 4 skin markers placed on the dorsal midline of their trunk were recorded while trotting on a track in the conditions of the routine lameness examination. The vertical displacements of the trunk markers underwent Fourier analysis. Results indicated that these displacements could be represented using only the first and second harmonics. From these two harmonics, indices were then developed. The sensitivity of these indices to the different types of experimental errors was also studied. Results showed that the values of the indices of the lame horses were relatively unaffected by the experimental errors. In lame horses, these indices allowed the quantification of the degree of the lameness, the identification of lame limb with a reliability > 95% and the characterisation of the type of trunk movements. These indices could be easily implemented in a computer program to provide objective information to the clinician or to be used as a first step in the development of an expert system. Moreover, these clinical tools may also be extended to other quadrupedal or bipedal locomotions.

A method to synchronise cameras using the direct linear transformation technique

The aim of this paper is to present a method which enables the recordings of cameras that are not equipped with a synchronisation system to be synchronised a posteriori. Using the Direct Linear Transformation technique, this method estimates the phase difference between two cameras by minimising the reconstruction errors of a moving point. Once the phase difference value is known, one of the recordings is chosen as a reference and the second one is synchronised to the first by cubic spline interpolation.

Remodeled-matrix contraction by fibroblasts: numerical investigations

It is well known that the fibroblast-collagen-matrix contraction model is a unique way to study mechanical interactions that regulate wound contraction of connective tissue cells. This contraction, due to cell traction, plays important roles in wound healing and pathological contractures. A continuum model initially used for the study of mesenchymal morphogenesis is revisited and numerically investigated by assuming that the extracellular matrix has adaptive-elastic properties. The set of non-linear partial differential equations is solved numerically by a finite difference method and the obtained results are discussed.

Three-dimensional kinematic technique for evaluation of horse locomotion in outdoor conditions

THE KINEMATICS of equine locomotion has been studied for quite some time. Muybridge and Marcy were the first to use the newly available photographic technology to document the gait of horses (MUYBRIDGE, 1887 and MAREY, 1894). Owing to the significance of lameness in horses and its economic significance for the horse industry, kinematics has been studied using increasingly sophisticated techniques adapted from human biomedical research (LEACH and DAGG, 1983; LEACH, 1987; CLAYTON, 1991). Horses present some particularities which make the study of their locomotion similar to that of the human athlete. Owing to their size and the amplitude of their movements, a broad field of view is required. Consequently, the captors have to be situated far from the horse subject, thus limiting the use of many human gait analysis systems. There are few kinematic analysis systems currently used for horse locomotion evaluation. They are divided into cinematographic, opto-electronic and video systems. Cinematography has been used in several studies. The locomotion of Standardbreds running at high-speed (12 m s l ) has been studied (FREDEKICSON and DREVEMO, 1972; DREVEMO et aL, 1987). The locomotion of race horses has been analysed using 16 mm high-speed cameras (LEACH et al., 1984; CLAYTON, 1989; HOLMSTROM et aL, 1994). The technique has also been applied to lameness evaluation (CLAYTON, 1986; GmTLER, 1988; KOBLUK, 1989). The advantages of this method are the high resolution and the frame rates (between 100 and 500 Hz) of the cinematographic cameras. However, this method requires film processing, thus increasing the cost and time of analysis. Moreover, cinematography appears to be quite expensive and the above studies were made with a single camera. The 3-I3 reconstruction and the simultaneous comparison between both sides of the horse were impossible.

Influence of individual competition level on back kinematics of horses jumping a vertical fence.

REASONS FOR PERFORMING STUDY The costs and investments required for the purchase and training of showjumpers justify the need to find selection means for jumping horses. Use of objective kinematic criteria correlated to jumping ability could be helpful for this assessment. OBJECTIVES To compare back kinematics between 2 groups of horses of different competition levels (Group 1, competing at high level; Group 2 competing at low level) while free jumping over a 1 m vertical fence. METHODS Three-dimensional recordings were performed using 2 panning cameras. Kinematic parameters of the withers and tuber sacrale (vertical displacement, vertical and horizontal velocities), backline inclination and flexion-extension motion of the 3 main dorsal segments (thoracic, thoracolumbar and lumbosacral) were analysed. RESULTS Group 2 horses had a lower displacement of their withers and tuber sacrale from the end of the last approach stride until the first departure stride (P<0.05). As a result, they increased the flexion of their thoracolumbar and lumbosacral junctions during the hindlimb swing phase before take-off (P<0.05). However, withers and tuber sacrale velocities were slightly modified. Group 1 horses pitched their backline less forward during the forelimb stance phase before take-off and straightened it more after landing (P<0.05), probably indicating a more efficient strutting action of their forelimbs. CONCLUSIONS AND POTENTIAL RELEVANCE Because significant differences in back motion were found between good and poor jumpers when jumping a 1 m high fence, criteria based on certain back kinematics can be developed that may help in the selection of talented showjumpers.

MECHANICAL BEHAVIOR UNDER UNCONFINED COMPRESSION LOADINGS OF DENSE FIBRILLAR COLLAGEN MATRICES MIMETIC OF LIVING TISSUES

Bio-artificial tissues are being developed as replacements for damaged biologic tissues and their mechanical properties are critical for load-bearing applications. Reconstituted dense three-dimensional (3D) fibrillar collagen matrices are promising materials for tissue engineering, at the light of their interaction with fibroblasts.1,2 The mechanical properties of these fibrillar collagen matrices are now being characterized under unconfined compression loading for various strain rates and collagen concentrations. The data were compared to those obtained in the same conditions with a biological tissue, the rat dermis. The results show a very sensitive behavior to both the displacement rate, typical of biological soft tissues, and the collagen concentration varying between 5 and 40 mg/ml. The link between the mechanical properties and the microscopic structure of the collagen scaffolds show an increasing viscoelastic modulus with respect to the fibril density. It is found that the matrices at 5 mg/ml and the dorsal rat skin (DRS) exhibit similar stress–strain response when submitted to the same external unconfined compression load. Such results highlight the interest of these matrices as potential tissue substitutes.

A method for the determination of mechanical parameters in a porous elastically deformable medium : Applications to biological soft tissues

Abstract A further approach has been tentatively envisaged for the determination of the mechanical parameters characterizing the unsteady behaviour of soft biological tissues considered as porous, elastically deformable media, saturated with a viscous fluid. If the two solid and fluid phases are incompressible, the parameters to be determined are : the drained Young’s modulus and Poisson’s ratio, the permeability of the porous solid structure and the dynamic viscosity of the interstitial fluid. Standard ramp–relaxation tests have been performed in order to investigate the time evolution of the force acting upon tissular discoidal samples subjected to unconfined compressive strains, under controlled environmental conditions. For moderate compressive strains, such a response in resultant force, characterizing a stress diffusion phenomenon within the medium, can be analyzed using a spectral decomposition with orthogonal eigenvectors. Such an analysis reveals that the overall response is defined by its asymptotic behaviour during both compression and relaxation phases, leading to the evaluation of the Young’s modulus and Poisson’s ratio. Moreover, the determination of the relaxation time leads to the evaluation of the specific permeability of the structure—the dynamic viscosity of the fluid being already known. A few examples of experimental tests data, involving both rubber foam, myocardium tissue in passive state and fibroblastic biological collagenic gels, are presented here in order to illustrate and validate such a rheological methodology. Particular attention is paid to the relations between the poroelastic behaviour and microstructural parameters of the material, with an emphasis on possible nonlinear effects arising from these very deformable media.

Model of Nonlinear Viscoelastic Wall Rheology Applied to Arterial Dynamics

In modern cardiovascular research, one of the fundamental problems is the accurate determination of local flow patterns inside large arteries and their relation with pressure waves generated by the heart. Data for blood flow rates, wall shear stresses, and detailed velocity profiles (with localization of inflexion points, recirculation zone, and boundary layer separation) are necessary to study transport phenomena related to atherogenesis or instability and turbulence generation mechanism. Theoretic and experimental models for local hemodynamic studies, as they have most often been designed in the past, do not take into account the motion of the wall and, for analytic and experimental simplification purposes, consider only the rigid wall case. Nevertheless, in regard to the large strain generated inside the arterial tissues, radial motion of the boundary and associated convective effects in the blood dynamics have to be considered if a rigorous description of the hemodynamic events is required.

Three-dimensional Simulation of Quantitative Ultrasound in Cancellous Bone Using the Echographic Response of a Metallic Pin

Degenerative discopathy is a common pathology that may require spine surgery. A metallic cylindrical pin is inserted into the vertebral body to maintain soft tissues and may be used as a reflector of ultrasonic wave to estimate bone density. The first aim of this paper is to validate a three-dimensional (3-D) model to simulate the ultrasonic propagation in a trabecular bone sample in which a metallic pin has been inserted. We also aim at determining the effect of changes of bone volume fraction (BV/TV) and of positioning errors on the quantitative ultrasound (QUS) parameters in this specific configuration. The approach consists in coupling finite-difference time-domain simulation with X-ray microcomputed tomography. The correlation coefficient between experimental and simulated speed of sound (SOS)—respectively, broadband ultrasonic attenuation (BUA)—was equal to 0.90 (respectively, 0.55). The results show a significant correlation of SOS with BV/TV (R = 0.82), while BUA values exhibit a nonlinear behavior versus BV/TV. The orientation of the pin should be controlled with an accuracy of around 1° to obtain accurate results. The results indicate that using the ultrasonic wave reflected by a pin has a potential to estimate the bone density. SOS is more reliable than BUA due to its lower sensitivity to the tilt angle.

Mechanical Properties of Collapsible Tubes and Propagation of Large Amplitude Waves

Large amplitude pressure wave propagation through collapsible tubes are phenomenon which are thougth to be relevant to the flow through airways and blood vessels.