US Patent 9042621 Intra-operative surgical plan changing

A system and computer implemented method for use in determining the deviation of an intra-operative position of an orthopaedic implant from a planned position is described. The position of the orthopedic implant in the bone is defined by a plurality of implant position parameters. The distance of a plurality of anatomical features in a three dimensional model of the surface of the bone relative to a model of the implant at a first position is calculated. The first position corresponds to a first set of values for the implant position parameters. The distance of the plurality of anatomical features to a model of the implant at a second position in the bone is calculated. The second position corresponds to a second set of values for the implant position parameters, and the second position is different to the first position.