1. A method for generating a diagnostic image of an anatomical extremity for diagnosing arthrosis/arthritis therein, comprising the steps of: obtaining a first image of an extremity with a first imaging modality and obtaining a second image of said extremity with a second imaging modality different from said first imaging modality; loading each of said first and second images into a computer having an associated display and, in succession for each of the loaded images, automatically generating in the computer a default line model of the extremity and automatically displaying the image at the display with said default line model superimposed thereon, and allowing manual adaptation of said default line model, by interaction with said display, to produce a modified line model conforming to anatomical details in the displayed image, resulting in said first image with a first modified line model superimposed thereon and said second image with a second modified line model superimposed thereon; and automatically in said computer, superimposing and co-registering said first image and said second image by conforming said first modified line model and said second modified line model with each other, to produce said diagnostic image.