Yasin Kisioglu

The effect of proximal tibial corrective osteotomy on menisci, tibia and tarsal bones: a finite element model study of tibia vara

Proximal tibial open wedge osteotomy (PTO) is a corrective operation used in the surgery of lower extremities and is applied to patients with varus deformities for sufficient correction. The aim of the study was to evaluate whether the PTO can achieve decreased stress‐bearing on the tibia and tarsal bones in addition to correcting the mechanical axis of the lower limb in patients with tibia vara.

Burst Pressure Determination of Vehicle Toroidal Oval Cross-Section LPG Fuel Tanks

This study addresses the prediction of the burst pressures and burst failure locations of the vehicle toroidal liquefied petroleum gas (LPG) fuel tanks using both experimental and finite element analysis (FEA) approaches. The experimental burst test investigations were carried out hydrostatically in which the cylinders were internally pressurized with water. The FEA modeling processes of these LPG fuel tanks subjected to incremental internal uniform pressure were performed in the nonlinear field. Two different types of nonlinear models, plane and shell, were developed and evaluated under nonuniform and axisysm-metric boundary conditions. The required actual shell properties including weld zone and shell thickness variations were also investigated and used in the computerized modeling processes. Therefore, the results of the burst pressures and their failure locations were predicted and compared with experimental ones.

Comparison of the Lag Screw Placements for the Treatment of Stable and Unstable Intertrochanteric Femoral Fractures regarding Trabecular Bone Failure

Background. In this study, the cut-out risk of Dynamic Hip Screw (DHS) was investigated in nine different positions of the lag screw for two fracture types by using Finite Element Analysis (FEA). Methods. Two types of fractures (31-A1.1 and A2.1 in AO classification) were generated in the femur model obtained from Computerized Tomography images. The DHS model was placed into the fractured femur model in nine different positions. Tip-Apex Distances were measured using SolidWorks. In FEA, the force applied to the femoral head was determined according to the maximum value being observed during walking. Results. The highest volume percentage exceeding the yield strength of trabecular bone was obtained in posterior-inferior region in both fracture types. The best placement region for the lag screw was found in the middle of both fracture types. There are compatible results between Tip-Apex Distances and the cut-out risk except for posterior-superior and superior region of 31-A2.1 fracture type. Conclusion. The position of the lag screw affects the risk of cut-out significantly. Also, Tip-Apex Distance is a good predictor of the cut-out risk. All in all, we can supposedly say that the density distribution of the trabecular bone is a more efficient factor compared to the positions of lag screw in the cut-out risk.

Fatigue Performance Evaluations of Vehicle Toroidal Liquefied Petroleum Gas Fuel Tanks

In this study, fatigue performances of the vehicle toroidal liquefied petroleum gas (LPG) fuel tanks were examined to estimate the fatigue life and its failure locations using both experimental and finite element analysis (FEA) methods. The experimental investigations performed as accelerated fatigue tests were carried out using a hydraulics test unit in which the tanks were internally pressurized by hydraulic oil. The LPG tanks were subjected to repeated cyclic pressure load varying from zero to service pressure (SP) of the tank. The computerized FEA modeling of these tanks were developed in threedimensional (3D) form using nonuniform geometrical parameters and nonlinear material properties. These models were also subjected to zero-based high cycle fatigue pressure load considering the stress life approach. The FEA modeling process was also simulated in nonhomogeneous material conditions. Therefore, the fatigue life performance and failure location of the toroidal LPG fuel tanks were predicted using the computer-aided simulations and compared with the experimental results. [DOI: 10.1115/1.4035976]

The effect of cement on hip stem fixation: a biomechanical study

This study presents the numerical analysis of stem fixation in hip surgery using with/without cement methods since the use of cement is still controversial based on the clinical studies in the literature. Many different factors such as stress shielding, aseptic loosening, material properties of the stem, surgeon experiences etc. play an important role in the failure of the stem fixations. The stem fixation methods, cemented and uncemented, were evaluated in terms of mechanical failure aspects using computerized finite element method. For the modeling processes, three dimensional (3D) femur model was generated from computerized tomography (CT) images taken from a patient using the MIMICS Software. The design of the stem was also generated as 3D CAD model using the design parameters taken from the manufacturer catalogue. These 3D CAD models were generated and combined with/without cement considering the surgical procedure using SolidWorks program and then imported into ANSYS Workbench Software. Two different material properties, CoCrMo and Ti6Al4V, for the stem model and Poly Methyl Methacrylate (PMMA) for the cement were assigned. The material properties of the femur were described according to a density calculated from the CT images. Body weight and muscle forces were applied on the femur and the distal femur was fixed for the boundary conditions. The calculations of the stress distributions of the models including cement and relative movements of the contacts examined to evaluate the effects of the cement and different stem material usage on the failure of stem fixation. According to the results, the use of cement for the stem fixation reduces the stress shielding but increases the aseptic loosening depending on the cement crack formations. Additionally, using the stiffer material for the stem reduces the cement stress but increases the stress shielding. Based on the results obtained in the study, even when taking the disadvantages into account, the cement usage is more suitable for the hip fixations.

How does the material variation of dynamic hip screw affect the cut-out risk in the treatment of intertrochanteric femoral fractures?

The material selection of dynamic hip screw (DHS) is not usually considered from the point of mechanical effects. In this study, the effects of the titanium alloy and stainless steel DHS was investigated in the cut-out risk of femur using finite element analysis (FEA). Intertrochanteric femur fracture (IFF) (31-A2 type according to AO classification) was created in the 3D femur model obtained from computer tomography images. The DHS model was inserted to the fractured femur model in two different positions (inferior and middle). The material properties of DHS were defined for the FEA. The force applied to the femoral head was determined according to the maximum value that is observed during walking. The results show that the safest model was obtained in the middle placement of titanium alloy DHS according to the safety factor. Consequently, the use of stainless steel DHS for IFF could cause higher failure risk of DHS than the use of titanium alloy DHS.

Stress Distribution Comparisions of Fixed and Broken Fibula, a Finite Element Study

The purpose of this study was to compare load carrying capacity and stress distributions of broken fibula on lower extremity under the average body weight and moment using with three-dimensional finite element analysis (FEA). The finite element (FE) models were generated from patient’s computed tomography (CT) data images. The loading and the relevant boundary conditions selected according to average human body conditions for obtaining the stress distribution on tibia surface. According the all FE analysis fibula is an effective role for load carrying capacity on distal side of tibia. These FEA results showed that the loading characteristics of the fibula should be taken into account in planning medical and surgical operations.

Higher order regression functions result better fit for the calibration curve

Regression analysis is used to predict the dependent variables individually concerning the explanatory available variables and find out the “best fit” line or curve through a series of data in a graph. It is also minimizing the sum of the squares deviations of any experimental data points from the theoretical curve. An important aspect of this analysis is to ensure that the x values are as accurate as possible so that the equation of the regression analysis is valid. Polynomial regression equation allows data to be fitted in general case to any equation where the y values can be described as a function of the x values. Polynomial regression includes quadratic regression (using polynomial 2nd order), cubic regression (using polynomial 3rd order), and higher polynomial regression functions (4th, 5th, and 6th orders) such as logarithmic, exponential, and power regressions. When many points of data do not quite lie on one line, one of the proper polynomial regressions, for instance, exponential or quadratic curves can be used passing through all points approximately for the best fit rather than linear regression. The authors, Sparks et al. studied and obtained contact pressure in the hip joint using paper based Fuji Film sensors and reported the calibration curve for the contact pressures as a function of stain intensity in Figure A.1, Appendix A. As seen, the calibration curve of their contact pressures are fitted using the quadratic regression equation. However, the 2nd order curve used in their study is not suitable to represent their calculated parameters for an appropriate fit especially for the higher x values, for example, y 1⁄4 1.875 MPa for x 1⁄4 200, considering the equation in Figure A.1. But, y value can be seen about 3 MPa for x 1⁄4 200 as seen in the graph. It is necessary to select a suitable regression equation to represent the best fit of the data. Based on the ideas given in Ref., using a 5th order curve is an appropriate approach for the best fit of the Fuji-film calibration data characteristics. In addition, the 5th order regression equation used by Muriuki et al. in their studies that shows the best fit. Therefore, the authors are suggested to use higher order regression equation to represent more precise fit of their calibration data.