A form of a support implant used in revision total hip arthroplasty (THA) should be diagnosed periodically because it may be distorted or broken. This paper proposes a new method that estimates the strength of stress on the support implant using finite element method (FEM) and genetic algorithm (GA). 3D sectional images of the support implant in vivo are acquired from multidtector-row computed tomography (MDCT) devices. The proposed method searches for a model whose shape is same as the support implant in MDCT images using GA. The database consists of many parts of the support implant that are generated by FEM with various patterns of strain. Direction and strength of the stress are estimated from the searched model. As a result of the proposed method applying to simulated MDCT images of horseshoe-shaped phantoms, the proposed method found the correct model. Also, the method detected the strain within the error of 1.03?0.38mm and 33.0?12.3N. Additionally, we applied the method to MDCT images of 2 patients after THA. The results showed that the direction and the strength of the stress were successfully estimated.