Abstract
The main reasons of aseptic loosening of the cemented hip stem are three: Bone cement fracture, bone cement debonding, and rupture of cement/bone interface. These are caused by normal/shear stress in the cement mantle. In past studies, there are introduced some optimum design of the hip prosthesis. But all there are not considered enough design objectives. The purpose of this study is to design the optimum stem geometry, which reduces the many stress in the cement mantle at the same time. We reserched the relationship between stem design and cement mantle stresses for this purpose.
The cemented THA proximal femur FEM model was created on CAD and FEM software. Harris Precoat Design was used for stem model. Seven design parameters were defined on this model. Optimization calculation was performed by changing the design parameters. Four objective functions were defined; largest maximum principal stress in the cement mantle, stem/cement interface shear stress, bone/cement interface shear stress, and tensile stress between stem and cement mantle on proximal lateral section. Genetic algorithm was used to change the design parameters. Pareto map was created from results of calculation to reserach the realtionship of each objective functions.
From Pareto maps, we can know that Principal stress and Tensile stress are trade-off relation; the geometry decreasing Princpal stress is increasing Tensile stress. However, stem/cement shear and bone/cement shear are similar. Principal stress and shear stress are also similar.
Multicriteria design optimization of the hip prosthes is was performed based on the HARRIS Precoat stem. In the results, we got many Pareto solutions and relationship between each objective function. And with general methods of development, analysis of trade-off relationship is very useful method for Hip prosthesis development.
Correspondence should be addressed to Richard Komistek, PhD, International Society for Technology in Arthroplasty, PO Box 6564, Auburn, CA 95604, USA. E-mail: ista@pacbell.net
