Improved design of cementless hip stems using two‐dimensional functionally graded materials

Abstract

Increasingly, it is acknowledged that bone resorption around cementless hip implants may cause future problems. The solution is frequently sought in reducing implant stiffness. However, this confronts the designer with a true design conflict: how to reduce the stiffness without excessively loading the proximal bone/prosthesis interface? The aim of this work is to improve the design of cementless hip stem material, using two-dimensional (2D) functionally graded material (FGM) concept in order to solve the above problems. Two models were used in this analysis, using three materials with different elastic moduli, E(1), E(2), and E(3). In model I, the elastic moduli E(1) and E(2) gradually change along the upper stem surface, while E(3) is maintained constant along all the lower surface of the stem. However, in model II, the elastic moduli E(1) and E(2) gradually change along the lower stem surface, while E(3) is maintained constant all along the upper stem surface. It is found that the recommended model is model I, which has three distinct materials of hydroxyapatite, Bioglass, and collagen. The recommended design of 2D FGM is expected to reduce the stress shielding by 91% and 12%, respectively, compared with titanium stem and model II of FGM. It is found that this new design reduces the maximum interface shear stress at the lateral and medial sides of the femur by about 50%, compared with titanium stem. Furthermore, the maximum interface shear stress is reduced by about 17% and 11% at the lateral and medial sides of the femur, respectively, compared with that of model II of FGM.

Multiscale Design and Multiobjective Optimization of Orthopedic Hip Implants with Functionally Graded Cellular Material

“…These data have been obtained from the work of Kuiper and Huiskes [14]. The 3D geometry of the femur is simplified into a 2D model where the thickness of the stem and bone varies such that the second moment of area about the out-of-plane axis does not differ in both models [16]. Furthermore, in this paper, the implant material is designed to be an open cell lattice to ease bone in growth in the implanted stem and obtain a full bond.…”

“…As a result, the whole set of trade-off designs could not have been captured. Hedia et al [16,17] attempted to reconcile the conflicting nature of these objective functions by proposing the use of three bioactive materials: hydroxyapatite, Bioglass, and collagen, to design a graded cementless hip stem. Although their implant design reduced bone résorption and bone-implant interface stresses, the use of such bioactive materials have limitations due to their brittleness and insufficient strength when applied to load-bearing applications [18][19][20].…”

Comparison of Various Functionally Graded Femoral Prostheses by Finite Element Analysis

“…They performed a simplified 2D FEA and applied a vertical load of 3 kN on the femoral prosthesis. Hedia et al [27, 28] made a 2D model of prostheses composed of FGMs and different gradient directions and accessed their performance by a 2D FEA. They showed more stress in the bone and reduction in interface stress owing to the use of the FGMs in the femoral prosthesis.…”

Optimum Functionally Gradient Materials for Dental Implant Using Simulated Annealing

“…The other issue needs to be systematically studied is how to devise an optimal FGM pattern for dental implant application. It has been widely accepted that a mating mechanical property to the host bone should be made in order to avoid stress shielding (Hedia & Mahmoud, 2004;Hedia et al, 2006) and promote osseointegration and bone remodeling (Chu et al, 2006;Yang & Xiang, 2007). However, there are few reports available which examine whether or not a mating property could result in the best remodeling consequence and ensure a long-term success.…”