Simulation of the femoral cut for total knee arthroplasty was performed in 44 knees using three-dimensional computed tomography. The three-dimensional images were measured, and the shape of the femur was compared to the provided femoral prosthesis. The ratio between the medial-lateral and anteroposterior dimensions of the three-dimensional images did not always match the prosthesis. The widths of the medial condyles of the three-dimensional images tended to be larger than those of the prosthesis. The lengths of the lateral posterior condyles of the three-dimensional images tended to be shorter than those of the prosthesis. These results suggest that a new prosthesis should be designed to achieve a better anatomical fit.