Parametric Analysis of Orthopedic Screws in Relation to Bone Density
Elisabetta M Zanetti*, 1, Massimiliano Salaorno1, Giovanni Grasso1, Alberto L Audenino2
Identifiers and Pagination:Year: 2009
First Page: 19
Last Page: 26
Publisher Id: TOMINFOJ-3-19
Article History:Received Date: 23/1/2009
Revision Received Date: 22/2/2009
Acceptance Date: 18/3/2009
Electronic publication date: 21/4/2009
Collection year: 2009
open-access license: This is an open access article licensed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited.
A global study of geometry and material properties of orthopedic screws was performed, considering not only the effect of each single factor (screw pitch, number of threads, fillet angle, etc.) but also their interactions with respect to bone density.
The stress patterns resulting from different screw geometries and bone densities were analyzed using finite element techniques, taking into account different levels of osseointegration between the screw and the bone. These numerical models where validated through experimental pull-out tests, where a pull out force of 120 N produced localized failure of the last thread (stresses above 0.42 MPa). The results of the numerical simulations were then summarised using a multi-factorial parametric analysis. This demonstrated the great relevance of the interaction between bone density and screw pitch, showing that the optimal screw pitch can vary by more than 25% for different densities (0.35 g/cm3 and 0.47 g/cm3, respectively).
The parameters calculated by means of the multi-factorial analysis allow the pull out force to be estimated for different osseointegration levels, different screw geometries and material properties, and for different bone densities. The final objective is to determine the best choice of implant for each individual patient.