1. A method for generating a 3D knee joint image, comprising: generating a statistical shape model by using previously generated sample knee bone images; generating a knee joint bone image by segmenting a bone region from an input knee image using the statistical shape model; generating a keen joint cartilage image by segmenting a cartilage region from the knee joint bone image; and generating a 3D knee joint image for the input knee image by composing the knee joint bone image with the knee joint cartilage image.