Desi̇gn and analysi̇s of total knee replacement's ti̇bi̇al component wi̇th latti̇ce porous structure

Joints are the structures of our body that allow people to move. There are many joints in different parts of our body. One of these, the knee joint, bears the entire load of the human body. This aspect causes the knee joint to be damaged. Solutions were sought to restore the function of the worn joint and knee implants were discovered. One of these is the total knee replacement. Many studies have been carried out on it, and implant technology is constantly renewing itself in terms of its compatibility with our body structure, that is, close to the originality of the joint and helping to eliminate movement restrictions. The most prominent developments in recent years can be said to be that implants have a porous structure and are produced with three-dimensional printing. In this technology, since the implants come into contact with the bone when placed in the body, the areas in contact with the bone are designed with a porous structure, just like bone. The aim of the implant design to resemble the porous structure of bone is to make it easier for the implant to adapt to our body when we place it in our body. The concept of biocompatibility is used here. Another advantage of the porous structure is that it improves the mechanical properties of the model in which it is used. It adds lightness and durability to the model. The feature of lattice structures is included in obtaining the most biomechanically correct pore design. Lattice structures are used today in implant technology and in many areas. It does not lose its currency due to its positive contributions to different sectors. This creates an ever-developing field of study with different perspectives. The existence of many types of lattice structures also increases the diversity of work.Different lattice structure implant designs have been made and are still being made. By incorporating lattice structures into the implant design, the implant reduces the stiffness closer to the bone. Important points in lattice structure designs; were the cell size and porosity (volumetric space) of the lattice structure. The decrease in cell size and increase in porosity gives the implant the desired mechanical properties. In order to obtain the most accurate design, implant models designed and produced in a lattice structure were subjected to biomechanical tests and analyses, and the results were examined and evaluated.In order to contribute to the current field of study, a study on total knee replacement and lattice structures was carried out in this thesis study. The total knee replacement consists of three components. These are the shin component, the thigh component and the plastic spacer. Only the tibial component was studied. The tibial component was designed in a lattice structure and its static analysis was carried out by applying biomechanical loads and using the finite element method. The analysis results were evaluated from a biomechanical perspective.First, the tibial component and the tibial cortical bone were designed in three dimensions in SolidWorks, one of the computer-aided design programs. Considering that the implants, which are the target of the study, should be designed with a lattice structure, the tibial component was designed with a lattice structure using the Creo Parametric program. Only the surfaces of the component in contact with the shin bone can be designed in a lattice structure. For this reason, the preferred part for filling the tibial component with the lattice structure was the lower part of the component tray. Three different lattice structures were preferred: BCC, rhombic dodecahedron and truncated octahedron. As a result, tibial component models with three different lattice structures were obtained. The cell size of the lattice structures used in these models is 10 mm, the strut diameter is 2 mm, and their porosity varies between 59% and 67%. The tibial component, which is a solid model not filled with a lattice structure, and the tibial component in these three lattice structures were first transferred to the Hypermesh program to perform analysis. In this program, the process of eliminating model geometry errors, creating the mesh structure, defining the material and boundary conditions were made, and models prepared for this were obtained before moving on to the analysis step. These tibial component models were transferred to the Abaqus/CAE program and finite element analyzes were performed. When the analysis was completed, maximum von Mises stress, logarithmic strain and displacement information were obtained.It was determined that the model that showed the lowest von Mises stress value was the rhombic dodecahedron lattice structured tibial component. By using this lattice structure, it was desired to observe the shin component analysis results at different porosity values. Analysis of the rhombic dodecahedron lattice structured tibial component model with 60% porosity is available. Two new models with porosity of 48 and 80 percent were designed and analyzed using the same steps. With the increase in porosity, maximum von Mises stress, logarithmic strain and displacement values increased.In the literature, porosity between 50-90% refers to the bone porosity value range. It has also been stated that the lattice structure with porosity over 70% is within the cortical bone elastic modulus value range. 80% porosity provides the desired mechanical properties for the lattice structured model. With the support of this information, the lattice structure tibial component with 80% porosity was assembled with the three-dimensionally designed tibial cortical bone. Simulation of the surgical placement of implants into our body can be done with analysis programs.Expectations from knee implants: It shows accepted mechanical properties, eliminates the complications that may occur in the knee, reduces the pain experienced, increases the functionality of the knee without causing any limitation in the daily activities of the person and increases the quality of life of the person. These expectations can be interpreted according to the analysis results.In order to evaluate the mechanical suitability of the total knee replacement tibial component in the lattice porous structure created within the scope of the study for use in the human body, general contact was defined between the tibial cortical bone and the component and friction was simulated. Before analysis, this new model was analyzed by applying the steps applied to other models. By including different values for some parameters in the analysis, the analysis results were intended to be interpreted according to the changing parameters. In this context, different values are included in the friction force value defined between the bone and the implant, the force value applied to the upper surface of the tibial component, and the material type parameters. Analyzes were made for three different friction forces, four different forces and three types of materials. To examine the change of each parameter, the other two parameters were kept constant. For example; In order to examine the effect of friction force change on maximum von mises stress, logarithmic strain and displacement values, the force and material information to be applied to the shin component surface will remain constant. Thus, the results of a total of eight different analyzes were obtained and these data were interpreted.According to the information obtained from the study, as the force value increased, each of the stress, strain and displacement increased. The knee implant is expected to be able to withstand biomechanical loads of three times the human weight. It has been observed that the implant is extremely durable against these three applied force values. When the strain result of the applied force below this value is examined, it is determined that it does not show a value within the required range. It can be said that it will cause bone atrophy due to the stress shielding. Analysis was carried out with the values determined as the friction coefficient and the results were compared. As the stress value decreases and the friction coefficient increases, micromobility on the contact surface of the bone and implant decreases. The strain values for all three friction coefficients were found to be within the specified range and were found to be at a value that would not cause bone fracture. The results obtained when Ti6Al4V, CoCrMo and stainless steel material information were defined as materials were compared. Ti6Al4V material showed the highest result for displacement value. It is stated that it will deform more easily than other materials. The strain values for all three friction coefficient values are within the specified range and are at a level that will not cause bone fractures. As a result, all shin component models designed with a lattice porous structure did not exceed the limit provided by the material properties. This is decided by considering the yield strength values of the materials.The lattice structures used in this study alleviated the tibial component. In addition to this lightness, the contribution of mechanical properties to increasing the biocompatibility of the implant cannot be ignored. This contribution is that when the implant comes into contact with the tibia bone, the volumetric gaps created by the lattice structure allow the bone to grow inwards. It also reduces bone resorption.In summary, as porosity increases, tibial component volume decreases and supports bone growth.