The Design of an Optimal Femoral Hip Prosthesis To Reduce Stress Shielding
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Date
2006
Authors
Shuib, Encik Solehuddin
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Abstract
Operation of inserting an implant into il femur was necessary for damaged and fractured hip joint. Through
the implant, patient could continue their daily activities although not as active as before the operation.
However, effects from hip replacement might reduce the natural stress distribution of the femur. The
reduction could cause its density and volume shrinkage. The implant might loosen and causes pain to
patients, thus needed a revision surgery. The phenomenon of reduction in toad was identified as stress
shielding.From a simple composite beam theory, implant material and its cross-sectional area would mostly
affect the load distribution in femur (Fi/F). Implant materials with higher modulus of elasticity compared with
femur such as Titanium (Ti) and Cobalt-chromium (Co-Cr) would reduce Ft/F to 43.04% and 58.23%. It
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would also reduce to 19.54% in iso-elastic, 55.22% (Ti) and 64.29% (Co-Cr) when implant diameter
increased from 6 mm to 14 mm. However, hollow implant would increase the Fi/Fto 15.19% (iso-elastic),
73.33% (Ti) and 109.10% (Co-Cr) as compared with solid implant.
T apology optimisation method was employed in the analysis of model of implant, cement and
femur in 3-dimension by using ANSYS 7 .1. The analysis was performed with the assumption that the
models responded linearly, isotropic and also homogeneous. A compressive load was applied at the
proximal end of the implant and a reaction from muscle of greater trochanter occurred during walking were
used in the analysis. Reactions from other muscles were neglected. Model was constrained at the distal
end of femur along x, y and z-axes. The objective of the optimisation was to minimise implant compliance
(maximise implant stiffness) subjected to percentage of reduction in its initial volume (Vo) ranges from 30%
Vo up to 70% Vo. Results showed that implant with 50% Vo or 60% Vo would produce closed boundary and
hence were acceptable in shape.
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Mechanical Engineering