1. A method for designing a customised surgical instrument or prosthesis for a body part of a specific patient, comprising: processing at least one x-ray image of the body part to generate a processed patient image; instantiating a statistical model generated using a minimum description length approach and having a dense set of anatomical correspondence points across the model using image data derived from the processed patient image to generate a patient specific model of the body part having a high accuracy surface; and using patient specific data from the patient specific model to generate a design of the customised surgical instrument or prosthesis for use in a surgical procedure to be carried out on the body part.