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Research Papers

Comparison Between DEXA and Finite Element Studies in the Long-Term Bone Remodeling of an Anatomical Femoral Stem

[+] Author and Article Information
A. Herrera1

Department of Surgery, University of Zaragoza, Spain, Domingo Miral s/n, 50009 Zaragoza, Spain; Department of Orthopaedic Surgery and Traumatology, Miguel Servet University Hospital, Paseo de Isabel la Católica 1-3, 50009 Zaragoza, Spainaherrera@salud.aragon.es

J. J. Panisello

Department of Surgery, University of Zaragoza, Spain, Domingo Miral s/n, 50009 Zaragoza, Spain; Department of Orthopaedic Surgery and Traumatology, Miguel Servet University Hospital, Paseo de Isabel la Católica 1-3, 50009 Zaragoza, Spain

E. Ibarz, J. Cegoñino, L. Gracia

Department of Mechanical Engineering, University of Zaragoza, Spain, María de Luna 1, 50018 Zaragoza, Spain

J. A. Puértolas

Department of Science and Technology of Materials, University of Zaragoza, Spain, María de Luna 1, 50018 Zaragoza, Spain

1

Corresponding author.

J Biomech Eng 131(4), 041013 (Mar 09, 2009) (11 pages) doi:10.1115/1.3072888 History: Received June 07, 2007; Revised August 27, 2008; Published March 09, 2009

The implantation of a cemented or cementless femoral stem changes the physiological load transfer on the femur producing an effect on the bone called adaptative remodeling. The patterns of this remodeling are attributed to mechanical and biological factors, and those changes in bone mineral density have been determined in long-term densitometry studies. This technique has proved to be a useful tool able to quantify small changes in bone density in different femoral areas, and it is considered to be ideal for long-term studies. On the other hand, the finite element (FE) simulation allows the study of the biomechanical changes produced in the femur after the implantation of a femoral stem. The aim of this study was to contrast the findings obtained from a 5 year follow-up densitometry study that used a newly designed femoral stem (73 patients were included in this study), with the results obtained using a finite element simulation that reproduces the pattern of load transfer that this stem causes on the femur. In this study we have obtained a good comparison between the results of stress of FE simulation and the bone mass values of the densitometry study establishing a ratio between the increases in stress (%) versus the increases in bone density (%). Hence, the changes in bone density in the long term, compared with the healthy femur, are due to different load transfers after stem implantation. It has been checked that in the Gruen zone 7 at 5 years, the most important reduction in stress (7.85%) is produced, which coincides with the highest loss of bone mass (23.89%). Furthermore, the simulation model can be used with different stems with several load conditions and at different time periods to carry out the study of biomechanical behavior in the interaction between the stem and the femur, explaining the evolution of bone density in accordance to Wolff’s law, which validates the simulation model.

FIGURES IN THIS ARTICLE
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Copyright © 2009 by American Society of Mechanical Engineers
Topics: Stress , Bone , Density , Prostheses
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Figures

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Figure 6

Principal minimum stress in the cortical and cancellous bones of the femur with prosthesis ABG-II

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Figure 7

Bone mass and average von Mises stress versus time for the femur with prosthesis ABG-II

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Figure 8

Variation in bone mass (%) and average von Mises (%) stress variation versus time for the femur with prosthesis ABG-II in the Gruen zones

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Figure 9

Average von Mises stress increase (%) versus bone mass increase (%) for the femur with prosthesis ABG-II in the Gruen zone 7

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Figure 5

Load flows in the healthy model and in the model with prosthesis

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Figure 4

Principal maximum stress in the cortical and cancellous bones of the femur with prosthesis ABG-II

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Figure 3

Bone mass and average von Mises stress versus time for a healthy femur

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Figure 2

(a) FE model of the healthy femur with boundary conditions and detail of the mesh in the proximal area; (b) FE model with boundary conditions of the femur with prosthesis ABG-II and detail of the mesh in the proximal area

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