Mechanical failure of the cemented hip stem is mainly caused by several cement mantle problems such as cement fracture. Geometries of the cement mantle and the stem are important factors of failure risks. Shape optimization, especially multi-objective optimization, is required to solve these design problems, because the cement fracture is caused by multiple factors. In this study the stem design was optimized using a genetic algorithm suitable for multi-objective optimization. A three-dimensional finite element model of the proximal femur was developed. Two objective functions, the largest maximum principal stresses of proximal and distal sections in the cement mantle, were used. The Neighborhood Cultivation Genetic Algorithm (NCGA) was introduced to minimize these two objective functions. In the results, geometry that decreases the proximal cement stress and the geometry that decreases the distal cement stress were not consistent. The distal cement stress decreased with decreasing distal stem width and decreasing proximal-lateral section width. However, it led to increase of the proximal cement stress. The method in this study can be easily applied to another calculating conditions. The multi-objective optimization with genetic algorithm is useful for shape optimization of the cemented hip stem to avoid cement fracture.
