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Experiment-based FE simulation of oncology knee endoprosthesis

Zach L., Konvickova S., Ruzicka P.

Engineering of Biomaterials

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2011

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Vol. 14, no. 106-108

10--12

EN

This paper presents two FE simulations of an oncology knee-joint endoprosthesis. Firstly dynamic experiment-based analysis traditionally made on special knee simulator has been calculated. Another FE simulation of an oncology knee-joint endoprosthesis was made on a complex model based on previously developed geometric model of a lower limb. The presented paper aims to prove the potential of finite element method in biomechanics, especially in development of joint endoprosthesis.

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Finite element analysis of oncology knee endoprosthesis

Zach L., Konvickova S., Ruzicka P.

Engineering of Biomaterials

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2009

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Vol. 12, no. 89-91

9--11

EN

This paper presents a finite element simulation of an oncology knee-joint endoprosthesis in a various degrees of flexion. The simulation has been made in accordance with an ISO 14243 [1-3]. A model of the knee implant (produces by ProSpon, s.r.o. [4]) consists of following parts: femoral stem, femoral replacement, femoral component, PE bushings, and tibial plateau. Results for four positions of flexion (1.53deg, 8.13deg, 15.31deg and 26.33deg) gave better understanding of strain and stress distribution along the endopros-thesis and pointed out also the most crucial areas requiring the attention. These foundlings are useful for individual design of the knee-joint prosthesis and for further development.

3

Develoment of a physiognomic hip joint replacement

Sykora J., Konvickova S., Daniel M.

Engineering of Biomaterials

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2009

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Vol. 12, no. 89-91

17

4

Limiting fiber extensibility model for arterial wall

Horny L., Zitny R., Chlup H., Konvickova S.

Engineering of Biomaterials

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2008

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Vol. 11, no. 81-84

112--113

EN

Arterial walls exhibit anisotropic, nonlinear and inelastic response to external loads. Moreover arterial wall is non–homogenous material with complicated internal structure. These facts make the question about the best material model for arterial wall still unanswered. Nowadays approach to building constitutive models is characterized by incorporating structural information when considering e.g. layers, fibers, fiber orientation or waviness. The most frequent method how to incorporate structural information is to regard arterial wall as a fiber reinforced composite. Considerations about preferred directions are subsequently implemented into the framework of continuum mechanics. Constitutive models are usually based on the theory of hyperelastic materials. Thus mechanical response of an arterial wall is supposed to be governed by a strain energy (or free energy) density function like in (1). The theory of hyperelastic materials is widely applied and studied in details in polymer science. Due to some phenomenological and structural similarities between rubber–like materials and biological tissues, methods of polymer physics are frequently applied in biomechanics, see Holzapfel [1]. Gent [2] suggested the new isotropic model for strain energy density function which was based on an assumption of limiting chain extensibility in polymer materials. The Gent model expresses strain energy y as a function of first invariant I1 of the right Cauchy-Green strain tensor as follows [formula]. In equation (1) μ denotes stress–like parameter, so–called infinitesimal shear modulus. Jm denotes limiting value of I 1 -3. The domain of logarithm requires [formula]. Thus, Jm can be interpreted as limiting value for macromolecular chains stretch. Horgan and Saccomandi in [3] suggested its anisotropic extension. They recently published modification based on usual concept of anisotropy related to fiber reinforcement, see paper [4]. Horgan and Saccomandi use rational approximations to relate the strain energy expression to Cauchy stress representation formula. We adopted this term with small modification as follows [formula] In (2) μ denote shear modulus. J m is the material parameter related to limiting extensibility of fibers. The similar definitional inequality like in (1) must be hold for logarithm in (2). Thus I 4 must satisfy [formula] denotes so called fourth pseudo–invariant of the right Cauchy-Green strain tensor which arises from the existence of preferred direction in continuum. It is worth to note that total number of invariants of the strain tensor is five in the case of transversely isotropic material and nine in the case of orthotropy. Details can be found in e.g. Holzapfel [5]. Model (2) presumes two preferred directions in continuum which are mechanically equivalent. Due to cylindrical shape of an artery we can imagine it as helices with same helix angel but with antisymmetric rientation. This is illustrated in the FIG. 1 I 4 can be expressed in the form given in (3) [formula] Stretched configuration of the tube is characterized by λ t , what denotes circumferential stretch and λ z what denotes axial stretch, respectively. Model (2) contains three material parameters. Above described μ, J m and β. The third material parameter β has the meaning of angle between fiber direction and circumferential axis. There are two families of fibers with angle ±β, however, I 4 is symmetric with respect to ±β. In order to verify capability of (2) to govern multi–axial mechanical response of an artery regression analysis based on previously published experimental data was performed. Details of experimental method and specimen can be found in Horny et al. [6]. Briefly we resume basic facts. Male 54–year–old sample of thoracic aorta underwent inflation test under constant axial stretch. The tubular sample was 6 times pressurized in the range 0kPa–18kPa–0kPa under axial pre–stretch λ z =1.3 and 3 times in the pressure range 0kPa–20kPa–0kPa under λ z =1.42, respectively. The opening angle was measured in order to account residual strains. Radial displacements were photographed and evaluated by image analysis. Regression analysis based on least square method gave the estimations for material parameters μ, Jm and β. The vessel was modeled as thick–walled tube with residual strains. The material was supposed to be hyperelastic and incompressible. No shear strains were considered. Fitting of material model was based on comparison of model predicted and measured values of internal pressure. Results are illustrated in FIG. 2. We can conclude that proposed material model fits experimental data successfully. Thus strain energy given in (2) is suitable to govern arterial response during its inflation and extension. Estimated values of parameters for material model (2) are as follows: μ =26kPa; J m =1.044; β=37.2°

5

Finite element analysis of lower limb

Zach L., Konvickova S., Ruzicka P.

Engineering of Biomaterials

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2008

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Vol. 11, no. 77-80

15--17

EN

This paper presents a finite element simulation of a human lower limb in a full extension after a knee joint arthroplasty. Aside a total knee endoprosthesis Medin Modulár (size 76, right knee) provided by Medin Orthopedics, a.s., Czech Republic, two long bones, femur and tibia were used. As for a load, more than 30 most important muscles of the lower limb and 8 knee ligaments were disigned. Compared with our former results, this model gives reduced stress and contact pressures values which were given by more realistic ankle and hip joint definition. Their distributions correspond our former findings.

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Static finite element analysis of lower limb

Zach L., Konvickova S., Ruzicka P.

Engineering of Biomaterials

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2007

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Vol. 10, no. 63-64

6-7

EN

The paper deals with a simulation by means of finite method of a natural lower limb after a knee joint arthroplasty in a full extension. Our last static model serving as a starting point for our future dynamic analysis is presented now. Aside a total knee endoprosthesis Medin Modular provided by MedinOrthopedics, a.s., two long bones, femur and tibia were used. Compared with our former results, this model gives reduced stress and contact pressures values which were given by more realistic ankle and hip joint definition. Their distributions also correspond better the experimental findings.

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Analysis of a contact stress distribution in new shape of a hip cup

Sykora J., Konvickova S., Daniel M.

Engineering of Biomaterials

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2007

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Vol. 10, no. 69-72

2-3

8

Modelling of temporomandibular joint and FEM analysis

Fricova M., Horak Z., Konvickova S.

Acta of Bioengineering and Biomechanics

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2006

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Vol. 8, nr 1

37-45

EN

The purpose of this paper is to develop a new complete replacement of the temporomandibular joint (TMJ). A three-dimensional finite element model of the temporomandibular joint has been developed according to the CT data. The model consists of a half skull, a half mandible and a temporomandibular joint disc. Stress analysis of TMJ during normal occlusion was carried out using non-linear finite element analysis (FEA). The model consists of 54 758 elements and 16 665 nodes. Material properties were obtained from previously published data and were considered to be isotropic and linear. Contact surfaces were defined between the temporomandibular disc and the mandibular condyle and between the temporomandibular disc and the fossa eminence on the skull. Between contact surfaces a finite sliding was allowed. Stresses in the TMJ components (disc, mandible condyle and the fossa eminence on the skull) were obtained. The results have shown stress distribution during normal occlusion.

9

Finite element analyses of modular knee joint replacement

Zach L., Konvickova S., Ruzicka P.

Inżynieria Biomateriałów

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2005

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R. 8, nr 47-53

22--23

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Development of new design of the acetabular component for total hip replacement

Sykora J., Konvickova S., Daniel M.

Inżynieria Biomateriałów

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2005

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R. 8, nr 47-53

19--20

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Testing of wear resistance of the ceramic materials for surgical implants

Sedlacek R., Konvickova S., Sochor M.

International Journal of Applied Mechanics and Engineering

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2002

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Vol. 7, Spec. is

47-50

EN

This article deals with very specific wear resistance testing of the biomaterials used for surgical implants. The abrasion is indispensable parameter for evaluation of the mechanical properties of these materials. This type of testing is very important for appreciation of new direction in total knee replacement, based on a new combination of biomaterials. The special wear resistance test is called "RING ON DISC". The experiments were carried out on the system MTS 858 MINI BIONIX placed in "Laboratory of Biomechanics of Man" at the Czech Technical University in Prague.