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Biomechanical comparison of a transiliac internal fixator and two iliosacral screws in transforaminal sacral fractures: a finite element analysis

Salasek M., Jansova M., Křen J., Pavelka T., Weisova D.

Acta of Bioengineering and Biomechanics

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2015

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Vol. 17, no. 1

39--49

EN

Purpose: Vertically unstable sacral transforaminal fractures can be stabilized with a transiliac internal fixator (TIFI) or two iliosacral screws (IS). This study was designed to compare stiffness between TIFI and IS. Methods: Using CT images finite element model of the pelvis was developed. Denis II type fracture was simulated and fixed either with TIFI or two IS. The sacral base was loaded vertically (250–500 N), displacement magnitudes on medial and lateral fracture surface and the maximum bone stress were calculated. The intact pelvis was used as a reference. Stiffness was determined by linear regression of load and displacement, computed stiffness ratio %. The von Mises stress was expressed as % ratio, evaluation of colour mapping was made. Results: The mean stiffness ratio medially in TIFI was 75.22%, in IS 46.54% ( p = 0.00005), laterally in TIFI 57.88%, in IS 44.74% ( p = 0.03996). The von Mises stress ratio of TIFI was 139.27%, of IS 565.35% ( p < 0.00001). Conclusions: Significantly higher stiffness and lower stress were found in TIFI model. TIFI provides a lower risk of over-compression of the fracture line in comparison with IS. TIFI thus exhibits superiority for fixation of transforaminal fractures, particularly with comminutive zone.

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ALE method in the fluid-structure interactions

Křen J., Žán J.

Zeszyty Naukowe Katedry Mechaniki Stosowanej / Politechnika Śląska

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2002

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z. 19

101-104

EN

The paper deals with an approach to the solution of the coupled fluid-structure interaction problem, where a viscous incompressible fluid and a rigid body-spring system interact with each other. In order to incorporate the effect of the moving surface of the rigid body, the arbitrary Lagrangian-Eulerian formulation is employed as the basis of the finite element spatial discretization. The semi-coupled numerical method is then used for the time integration of the equations of the motion.

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Introduction to an ALE continuum mechanics

Křen J.

Zeszyty Naukowe Katedry Mechaniki Stosowanej / Politechnika Śląska

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2001

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z. 16

85-91

EN

The paper presents an introduction to the arbitrary Lagrangian Eulerian method (ALE method) for the continuum motion description. The basic characteristics (motion, displacement, velocity and acceleration) and maps of the continuum are presented and used for determining the material time derivative and convective velocity in the ALE continuum formulation. Then they are used for the expression of the conservative laws in ALE description (weak and finite element approximations).

PL

W artykule przedstawiono wprowadzenie do zastosowania metody ALE do opisu ruchu continuum. Przedstawiono podstawowe charakterystyki (ruch, przemieszczenie, prędkość i przyspieszenie) oraz mapy ośrodka ciągłego oraz zastosowano je do określenia pochodnych materiałowych po czasie i prędkości konwekcyjnych w sformułowaniu ośrodka ciągłego z wykorzystaniem ALE. Następnie są wykorzystane do wyrażenia praw zachowania w opisie ALE.

4

Fluid-structure interactions in biomechanics of the urinary tract

Křen J., Horák M.

Zeszyty Naukowe Katedry Mechaniki Stosowanej / Politechnika Śląska

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1998

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z. 8

37-42

EN

The paper presents a simplified mathematical model of the interaction between the urine flow and the male urethra. Urine is assumed to be a newtonian fluid. The flow is considered as laminar. The wall of urethra featured by elastic properties undertakes large strains. When fully extended the urethra attains the shape of an axisymetric tube. An iterative method based on the uncoupled approach is developed.