Comparison of one-dimensional and two-dimensional functionally graded materials for the backing shell of the cemented acetabular cup.

Among the factors that have been suggested as contributing to the failure of a total joint replacement are stress shielding and the subsequent bone resorption. Recent studies have shown that when a backing shell made from a Ti alloy is used, high stresses are generated in the cement at the edges of the cup, and low stresses are generated at the dome of the bone in the acetabulum; thus, the bone at the dome suffers stress shielding and the cement edge suffers high stresses. The aim of this study was to investigate the effect of using a functionally graded material (FGM), instead of Ti alloy, for the backing shell (BS) on the stress distribution in the BS-cement-bone system. Finite-element and optimization techniques were used to obtain the optimal distribution of materials in the tangential direction only of the backing (1D FGM) as well as in the tangential and radial directions of the backing (2D FGM). It was found that the stress distribution in the BS-cement-bone system was about the same, regardless of whether the BS was fabricated from a 1D or 2D FGM. The stress-shielding factor in the bone at the dome of the acetabulum and the maximum von Mises stress in cement at the cement interfaces for 1D and 2D FGM were reduced by about 51%, 69%, and 50%, respectively, compared to the case when the shell was fabricated from a Ti alloy. The optimal elastic modulus of the 1D FGM was obtained with the materials graded from HA at the dome of the acetabulum to a Ti alloy at the rim of the shell. The optimal elastic modulus of the 2D FGM was obtained with the materials graded from Ti alloy at the right edge of the rim, to Bioglass 45S5 at the left edge of the rim, and to HA at the dome of the shell.

[1]  R Huiskes,et al.  Mathematical shape optimization of hip prosthesis design. , 1989, Journal of biomechanics.

[2]  Anthony Kelly,et al.  Comprehensive composite materials , 1999 .

[3]  Wang Shidong,et al.  Hydroxyapatite–Ti functionally graded biomaterial fabricated by powder metallurgy , 1999 .

[4]  R Huiskes,et al.  Mathematical optimization of elastic properties: application to cementless hip stem design. , 1997, Journal of biomechanical engineering.

[5]  D R Pedersen,et al.  An axisymmetric model of acetabular components in total hip arthroplasty. , 1982, Journal of biomechanics.

[6]  D. Dowson,et al.  A parametric analysis of the contact stress in ultra-high molecular weight polyethylene acetabular cups. , 1994, Medical engineering & physics.

[7]  T. SAMPATH KUMAR,et al.  Effect of TiO2-Ag2O additives on the formation of calcium phosphate based functionally graded bioceramics. , 2000, Biomaterials.

[8]  D T Davy,et al.  Effects of loading conditions and objective function on three-dimensional shape optimization of femoral components of hip endoprostheses. , 2000, Medical engineering & physics.

[9]  Hwj Rik Huiskes,et al.  Finite element analysis of acetabular reconstruction. Noncemented threaded cups. , 1987, Acta orthopaedica Scandinavica.

[10]  Mahmoud Nemat-Alla,et al.  Reduction of thermal stresses by developing two-dimensional functionally graded materials , 2003 .

[11]  D R Carter,et al.  Evaluation of bone cement failure criteria with applications to the acetabular region. , 1983, Journal of biomechanical engineering.

[12]  Motohiro Uo,et al.  Biocompatibility of materials and development to functionally graded implant for bio-medical application , 2004 .

[13]  D. Davy,et al.  Material optimization of femoral component of total hip prosthesis using fiber reinforced polymeric composites. , 2001, Medical engineering & physics.

[14]  Motohiro Uo,et al.  Development of Functionally Graded Implant and Dental Post for Bio-Medical Application , 2003 .