This article presents two FEА based parametric studies of a Selfdynamisable applied in treatment of fractures of the human thigh bone - femur. The main goal Internal Fixator (SIF), a medical fixation device developed by Prof. Mitkovic [1] , of these studies was to determine the sensitivity of fixator stress, which is related to its durability, to the changes of fixator configuration and fracture healing level. The expected benefit was the assistance in preoperative planning, which is especially valuable when less experienced surgeons are involved in the operative process or when complex traumas are treated. The follow-up research was also aimed at creating flexible and robust CAD and FE models of femur-fixator assembly that would enable an uninterrupted performance of structural optimization procedures.