Anatomical basis for the choice of the femoral implant in the total hip arthroplasty

There is within the population a considerable variation in the endosteal canal anatomy of the proximal extremity of the femur. This anatomical variation might jeopardize the result of the total hip arthroplasty when the surgeon uses a cementless femoral shaft. Indeed, if the secondary fixation of an implant stays under the dependency of many parameters, one has to obtain before anything else a very good primary stability, obtained by the morphological appropriateness of the bone-implant. The authors propose to define the cementless indications, as regards total hip arthroplasty, defining two radio-anatomical parameters: the Cortico-Medullary Index and the Femoral Flare Index.