Lukas Zach

Design, analysis and verification of a knee joint oncological prosthesis finite element model

BACKGROUND The aim of this paper was to design a finite element model for a hinged PROSPON oncological knee endoprosthesis and to verify the model by comparison with ankle flexion angle using knee-bending experimental data obtained previously. METHOD Visible Human Project CT scans were used to create a general lower extremity bones model and to compose a 3D CAD knee joint model to which muscles and ligaments were added. Into the assembly the designed finite element PROSPON prosthesis model was integrated and an analysis focused on the PEEK-OPTIMA hinge pin bushing stress state was carried out. To confirm the stress state analysis results, contact pressure was investigated. The analysis was performed in the knee-bending position within 15.4-69.4° hip joint flexion range. RESULTS The results showed that the maximum stress achieved during the analysis (46.6 MPa) did not exceed the yield strength of the material (90 MPa); the condition of plastic stability was therefore met. The stress state analysis results were confirmed by the distribution of contact pressure during knee-bending. CONCLUSION The applicability of our designed finite element model for the real implant behaviour prediction was proven on the basis of good correlation of the analytical and experimental ankle flexion angle data.

FE Simulation of Total Knee Endoprosthesis Loading during Stance

A finite element simulation of a human lower limb in a full extension after a knee joint arthroplasty is presented. Aside a total knee endoprosthesis Medin Modular (size 76, right knee) provided by MedinOrthopedics, a.s., Czech Republic, three long bones, femur, fibula and tibia were used. More than 30 most important muscles of the lower limb and 8 knee ligaments define main boundary conditions. Due to realistic ankle and hip joint definition, this model gives more accurate results compared with our former models.

CTG Annotator – Novel Tool for Better Insight into Expert-obstetrician Decision Making Processes

Cardiotocography (CTG) is monitoring of fetal heart rate (FHR) and uterine contractions (TOCO). Since 1960’s it is routinely used by obstetricians to detect fetal hypoxia. In theory, evaluation of the CTG in clinical setting is based on evaluation of macroscopic morphological features as suggested by internationally recognized FIGO guidelines.

Knee Joint Endoprosthesis Loading in Full Extension

This paper deals with a knee joint endoprosthesis finite element analysis. Based on a three dimensional geometric model of a lower extremity, a mechanical axis of the limb was designed. This axis is important for several reasons. Firstly, the endoprosthesis was positioned due to its direction, secondly, boundary conditions was defined on its proximal and distal end and finally, the axis enabled reasonable simplification of the model which led to the time saving analysis while preserving principal features of the model like the natural boundary conditions or knee joints degrees of freedom . Having this, one leg stance was simulated. Results of the analysis were encouraging for future models. Especially the choice of the mechanical axis was suitable and enabled a better distribution of contact pressures and stress on both femoral and tibial component compared to our former models. Also their magnitudes correspond better the manufacturers experience and our findings. The stresses did not exceeded 30 MPa for the UHMWPE tibial plateau and 100 MPa for the femoral component. The contact pressures were lower than 40 MPa.

STRESS ANALYSIS OF KNEE JOINT ENDOPROSTHESIS

Since we participate on development of knee joint replacement MedinModular (by Medin Orthopedics, a.s., Czech republic) [7], our aim is to assemble such a complex model, consisting of all bones of the knee and main muscle and ligamentous units, which could realistically simulate behavior of the human knee joint. In this article, newly assembled 3D geometrical model of the leg is presented. It is represented by all it’s main bones and a total knee replacement. Results of the first model are presented.

FEA of Human Knee Joint Replacement Using Real Bone Models

The aim of a project of our Laboratory of Human Biomechanics, CTU in Prague engaging finite element analyzes of a human knee joint is to create a finite element model as detailed as possible of this joint including its total replacement. On the basis of previous simplified models [1] and all existing mechanical tests, including those using special films for contact pressure measurement, new model was developed using a Walter Modular (WM) knee endoprosthesis. Bone three-dimensional models were created by common means using freely available CT scans (Visible Human Project [2]). Since it was necessary to be able to edit the bone models in a CAD software a procedure to obtain such models was executed. In these form, they can be used also during a development of new types of WM system. As for the analysis it self, it was prepared for the knee in a full flexion as a static contact problem loaded by a single force equal to three-times body weight. Since the static problem does not correspond to the real joint, another work has to be made and it is a goal of one of the next model. Results of the presented work are useful for a comparison with the results of another authors and our former ones.