Total hip arthroplasty (THA) is most likely one of the most successful surgical procedures in medicine. It is estimated that three in four patients live beyond the first post-operative year, so appropriate surgery is needed to alleviate an otherwise long-standing suboptimal functional level. However, research has shown that during a complete THA procedure, a solid hip implant inserted in the femur can damage the main arterial supply of the cortex and damage the medullary space, leading to cortical bone resorption. Therefore, this study aimed to design a porous hip implant with a focus on providing more space for better osteointegration, improving the medullary revascularisation and blood circulation of patients. Based on a review of the literature, a lightweight implant design was developed by applying topology optimisation and changing the materials of the implant. Gyroid and Voronoi lattice structures and a solid hip implant (as a control) were designed. In total, three designs of hip implants were constructed by using SolidWorks and nTopology software version 2.31. Point loads were applied at the x, y and z-axis to imitate the stance phase condition. The forces represented were x = 320 N, y = −170 N, and z = −2850 N. The materials that were used in this study were titanium alloys. All of the designs were then simulated by using Marc Mentat software version 2020 (MSC Software Corporation, Munich, Germany) via a finite element method. Analysis of the study on topology optimisation demonstrated that the Voronoi lattice structure yielded the lowest von Mises stress and displacement values, at 313.96 MPa and 1.50 mm, respectively, with titanium alloys as the materials. The results also indicate that porous hip implants have the potential to be implemented for hip implant replacement, whereby the mechanical integrity is still preserved. This result will not only help orthopaedic surgeons to justify the design choices, but could also provide new insights for future studies in biomechanics.
An external fixator device is a medical implant used to keep fractured bones stabilized and in alignment. It consists of pins which are placed into the bone, extending outside the surface of the skin, and attached to a rigid external rod to keep it in place. The aim of this study is to investigate the most suitable material used for the external fixator. Firstly, the 3D model of two unilateral uniplanar external fixator with the properties of titanium and stainless steel were constructed at Solidworks software with all the other parameters set to constant. Meanwhile, CT images of the lower limb were used to reconstruct a 3D model of the femur fracture at Mimics Medical software. Positioning and meshing of both the external fixator and the femur done at 3-Matics Medical and export as Patran for simulation at Marc Mentat software. 375 N load was applied at the most proximal femur to simulate stance phase of a gait cycle. From the findings, external fixator by using stainless steel as material properties have lower maximum von Mises Stress (18.40 MPa) at the femur and (103.69 MPa) at the fixator compared to the titanium (32.38 MPa) at the femur and (182.93 MPa) at the fixator. The result shows a difference of 75% of maximum von Mises Stress at the femur and the external fixator. Configuration by using stainless steel displaced 1.15 mm at the femur and 1.01 mm at the fixator which almost double value of displacement for titanium material for both femur (2.35 mm) and external fixator (2.11 mm). In conclusion, stainless steel external fixators provide better stability when compared to titanium external fixators.
Development of reconstructed three dimensional (3D) model of bones has successfully emerged from time to time. It is used in many engineering applications especially by researchers to help them in the simulation process through finite element analysis (FEA). Besides, the 3D model can also be used by surgeons with the help of engineers, in improving their pre-surgical planning and designing of patient-specific implants or surgical instruments. Focusing on the femur, this paper proposes a method in developing a reconstructed three-dimensional femoral bone model and verifying it through analysis by using the Finite Element Method. Load of 600N was applied on the most proximal point of the femoral head under axial loading. The strain value observed in the model were 0.35 mε, 0.242 mε, and 0.146 mε. These values were slightly higher than the value measured in cadaveric specimen in the previous study, but it showed the same pattern. Hence, it can be concluded that the development method is reliable.
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