Patient specific implant positioning

Instrument that is made to match the perimeter shape of a Patient Specific Knee Implant (PSKI) with features for locating holes in the distal femur such that the posts or lugs in the femoral implant locate the femoral implant centered medial-laterally within an acceptable degree of precision to prevent overhang of either the medial or lateral side of the femoral implant over the perimeter of the distal femur bone resections. Patient specific implant technology, in which a three-dimensional model of at least a portion of a bone is accessed and a three-dimensional solution volume is defined based on resection cuts used in fitting an implant on the portion of the bone. An outline representation of at least a portion of an outer surface of a periphery of the resultant bone volume is determined and the outline representation is used in one or more operations related to instrument matching.