Design and FEM Analysis of Porous Scaffold for Artificial Knee Joint Implant

Abstract

At present, the need for artificial joint replacement is increasing not only due to carefree lifestyle but due to development in medical field as well. It is important to consider the porosity factor while designing the implants as osteoporosis is a common phenomenon observed mainly in older people. In addition, stress shielding in well-fixed implants remains a significant clinical concern because conventional metals possess an elastic modulus much higher than bone, and predictable bone loss or hypertrophy has been observed. From a mechanical standpoint, to prevent stress shielding there are two ways of achieving stiffness parity of orthopaedic implants with bones, i.e. by reducing the amount of material used to construct the implant, thereby reducing its apparent stiffness, or secondly fabricating the implant from a material with a lower elastic modulus. The objective of this paper is to model artificial implant as porous scaffold and to study its behaviour under normal walking load condition with a maximum load of 750N. Test models were developed considering different diameters of axial through holes resulting in various porosities, i.e. 0, 5, 10, 15, 20, 25, 40, 50 and 60%. Finite element method is used to analyse these porous models. The von Mises stress of the designed porous scaffold continuously fluctuates for different values of porosity indicating the effect of porous bone on the failure of the artificial knee joint implant. At porosity of 40, 50, 60, von Mises stress is 15.25, 12.28, and 13.26 MPa. As the porosity level increases, the stress bearing capability at the interface reduces due to lesser area of the interface of the designed scaffold but there is an increase in deformation. Porosity between 40 and 50% is useful for reduced stress shielding effects as there are fewer areas to bear the load.