Evaluating the bone load share of a femur-nail set—an analytical stiffness model

The level of mechanical load that is been effectively shared between the nail and bone is an important consideration to be accessed to perform a good bone remodeling phase.

An analytical model based on the mechanics of solids, estimating the various encompassed stiffnesses, is presented. The cross-section modeling and the detailed load distribution between the bone and nail, through the different bone cross-sections, are provided. The results of the sharing load, and the consequent stress generation, were compared with the Finite Element (FE) model output.

The results show that the vertical force bone component is almost three times the transversal force. Also, the bone receives almost the double vertical load if compared to the nail. The bone bending moment components are, at least, one order of magnitude most significant than the torsional moment, and the bone shear stresses were, at least, one order of magnitude less significant than the bone normal stresses.

Medical decisions can be improved with the aid of the quantitative results generated by the proposed analytical model, based on mechanical engineering. It can improve, for instance, the selection of the appropriate nail in the function of the patient-specific femur stiffnesses. Also, it can contribute to the post-healing decisions, as to implement or not the nail dynamization.