الفهرس 
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Abstract
The human hip joint may be replaced in the treatment of patients suffering from degenerative and other diseases by an artificial one. This operation is known as total hip replacement (THR). The most common reason for THR is arthritis, reheumatoid, and osteoarthritise which can lead to serve pain and lack of function of this joint.
Stresses are generated in implant materials, bone, and at their interfaces. These stresses may affect the structural properties of implant/bone, system, or bring it to failure at some time in the post- operative period. Due to there stresses loosening and stress shielding become the important problems for long term survival of total hip arthroplasy.
This study describe a new method for material design optimization by using functionally graded material (FGM) for optimization of the stem and the metal backing shell of the acetabulum in the total hipprosthesis.
The aim of the new design is to reduce the possibility of fatigue fracture of cement by decreasing the stresses at the cement / bone and cement/ stem interfaces in the stem prosthesis and also decrease the stresses in cement at the cup edge of acetabulum at the same time decease the stress shielding effect and the likely incidence of bone resorption, whereby extend the expected life of the prostheses.
The geometry of the finite element model was taken from the proximal portion of the left femur of an old man with a high degree of accuracy. Nine contiguous longitudinal CT scan were obtained.
The actual dimensions of the model were generated using the analyzer software. A 2-D FE plan stress model with different thickness of stem cement and femoral bone components was developed to give similar results to those from the real 3-D geometry.
Software was written to calculate the fatigue notch factor in the cement/ stem and cement / bone interface and also cement/ MB interface as well as within the proximal bone and the central bone of the acetabulum (Dome) using the APDL(Ansys parametric design language) available with the commercial FE software package ANSYS. These notch factor are then optimized using the ANSYS program, using one factor as the objective function and the other four as constraints.
A material design optimization of the metal backing was carried out resulted HA/T1 as the optimal graded material which reduced the fatigue notch factor and the stresses at the rim at the same time increased the stress at the cement bone region (dome).
An optimal shape of the Paul Change stem was obtained which minimized the fatigue notch factor in the cement at the lateral stem/cement interfaces whilst constraining the fatigue notch factor in the cement along all other interfaces at or below its initial level and increasing the level of the stressing the proximal bone in order to decrease the stress shielding. The results was compared to the famous Charnley prosthesis and the two compared with the natural hipbone stresses.
A design optimization of material for the stem and the metal backing of the acetabulum were obtained, by using functionally graded materials, starting from the application of an axisymmetric simplified famous model of the hip prosthesis which minimized the fatigue notch factor in the cement/ stem interface whilst constraining the fatigue notch factor in the cement along all other interfaces at or below its initial levels and increase the fatigue notch factor of the proximal bone by using titanium/ hydroxyapatite FGM.
Shape and material optimization together were carried out by using the optimal shape of Chang stem model.
Functionally graded material design optimization resulted collagen / HA FGM as the optimal material design.
The comparison between the stresses of the famous charnley model and Chang model indicated that the new model decreased the stresses along the cement interfaces and increased the stresses at the proximal bone. The effect of that is lower bone resorption and lower probability of fatigue fracture of the cement.
This reduced possibility can extend the expected life of the prosthesis.
Finally the optimal design of total hip replacement increase the life of the operation.