The effect of locking screw threads on the fatigue strength in intramedullary nail fixation of femur fractures

Scott Lovald, Tariq Khraishi, Thomas DeCoster, Shahram Bozorgnia

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Fatigue failure of distal locking screws used in intramedullary nailing of fractures of the femur remains significant. To examine the notch effect of screw threads, the current study compares a threaded screw to an unthreaded peg according to generated stresses using the finite element method. The finite element method was chosen as analyses of this type facilitate the determination of the effect of a single controlled variable. Two analyses were run in the study. The first analysis considered the standard OrthoFix peg. The second analysis modified the peg to include a threaded portion along its length. The geometry of the nail and either the peg or screw was created in Pro-Engineer to the exact specifications of the implants. The minor (core) diameter of the screw was increased to be equal to that of the peg (i.e. there was more material in the screw than the peg). The boundary conditions simulated include a range of axial loads of 900 N to 2,400 N. According to all stress measures examined the peg will provide safer fixation when compared to the screw. The results suggest eliminating the thread from the length of the screw will increase fatigue strength by 64%. Accordingly the service life of a peg in a 270 Ib. human can be expected to be similar to that of a screw in a 164 Ib. human.

Original languageEnglish (US)
Title of host publicationSociety for Experimental Mechanics - SEM Annual Conference and Exposition on Experimental and Applied Mechanics 2009
Pages2436-2438
Number of pages3
StatePublished - Dec 1 2009
Externally publishedYes
EventSEM Annual Conference and Exposition on Experimental and Applied Mechanics 2009 - Albuquerque, NM, United States
Duration: Jun 1 2009Jun 4 2009

Publication series

NameSociety for Experimental Mechanics - SEM Annual Conference and Exposition on Experimental and Applied Mechanics 2009
Volume4

Other

OtherSEM Annual Conference and Exposition on Experimental and Applied Mechanics 2009
CountryUnited States
CityAlbuquerque, NM
Period6/1/096/4/09

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ASJC Scopus subject areas

  • Computational Mechanics

Cite this

Lovald, S., Khraishi, T., DeCoster, T., & Bozorgnia, S. (2009). The effect of locking screw threads on the fatigue strength in intramedullary nail fixation of femur fractures. In Society for Experimental Mechanics - SEM Annual Conference and Exposition on Experimental and Applied Mechanics 2009 (pp. 2436-2438). (Society for Experimental Mechanics - SEM Annual Conference and Exposition on Experimental and Applied Mechanics 2009; Vol. 4).