Masoud Torabi - PhD Student
Hamid Reza Chabok - Ph.D.Department of Biomedical Engineering, Collage of Engineering, Science and Research Branch, Islamic Azad university tehran iran

Bone screw is widely used devices for fixation of bone fractures or for stabilizing bone transplants. The fixation of the proximal or neck femur fractures by internal screw is one of the ordinary typical of the fixations. In this type of fixation, the screw glides into one bone fragment, which is thus united with another fragment by compressing against it when the screw is tightened. However, since the screw remains attached to the bony tissue after it was healed, it may also diminish the bone’s strength and stiffness The significantly stiffer metallic screw (elastic modulus) carries most of the shared load, causing the adjacent bone (elastic modulus) to be atrophied in response to the diminished load it is carrying, in accordance with Wolff’s law of functional adaptation. The ‘biomechanical compatibility’ of a particular screw with bone can, therefore, be characterized by the stress distribution developing in the bone around the screw as a result of the screw’s tightening during implantation. Thus the increasing of the stress shielding can be lead to unclench of the implant or screw during healing time, so the indicating of the type of the screws and specifying of parameters to create lower stress shielding is main purpose of this study. STP and SEDTP are parameters that used for evaluation of stress shielding. STP is the ratio of bone stress to screw stress and SEDTP is the ratio of bone strain energy density to screw strain energy density. Anyhow maximum STP and SEDTP is 1. With increasing of STP and SEDTP then stress shielding will be decreased and vice versa. Thus STP and SEDTP introduce implant biomechanical performance. Finite element method is a suitable method for indicating of the parameters. At first, with using of CT images, 3-D model will be created by Mimics then this model will be used in the finite element analysis

Stress shielding; STP; SEDTP; Finite Element Method