1. A method for classifying bone and cartilage in a magnetic resonance (MR) images, comprising: receiving, in a data processing system, an MR image testing model, the testing model including unclassified bone and cartilage portions; determining, by the data processing system, a testing volume of the testing model, the testing volume including areas of the testing model to be classified as bone or cartilage; modifying the testing model, by the data processing system, so that the testing volume corresponds to a mean shape and a shape variation space of an active shape model; producing an initial classification of the testing volume into bone areas and cartilage areas, by the data processing system, by fitting the testing volume to the mean shape and the shape variation space of the active shape model; producing a refined classification of the testing volume into bone areas and cartilage areas, by the data processing system, by refining the boundaries of the testing volume with respect to the active shape model; and segmenting the MR image testing model into different areas corresponding to bone areas and cartilage areas according to the refined classification.