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Research Papers

Assessing the Local Mechanical Environment in Medial Opening Wedge High Tibial Osteotomy Using Finite Element Analysis

[+] Author and Article Information
Yves Pauchard

Robarts Research Institute,
Western University,
London, ON N6A 5K8, Canada
Institute of Applied Information Technology,
School of Engineering,
Zurich University of Applied Sciences,
Steinberggasse 13, Postfach,
Winterthur CH-8401, Switzerland
e-mail: pauc@zhaw.ch

Todor G. Ivanov, Jaques S. Milner

Robarts Research Institute,
Western University,
London, ON N6A 5K8, Canada

David D. McErlain

Department of Radiology,
Faculty of Medicine,
University of Calgary,
Calgary, AB T2N 2T9, Canada

J. Robert Giffin

Schulich School of Medicine and Dentistry,
Western University,
London, ON N6A 5C1, Canada
Wolf Orthopaedic Biomechanics Laboratory,
Fowler Kennedy Sport Medicine Clinic,
Faculty of Health Sciences,
Western University,
London, ON N6A 3K7, Canada

Trevor B. Birmingham

Wolf Orthopaedic Biomechanics Laboratory,
Fowler Kennedy Sport Medicine Clinic,
Faculty of Health Sciences,
Western University,
London, ON N6A 3K7, Canada

David W. Holdsworth

Schulich School of Medicine and Dentistry,
Western University,
London, ON N6A 3K7, Canada
Wolf Orthopaedic Biomechanics Laboratory,
Fowler Kennedy Sport Medicine Clinic,
Faculty of Health Sciences,
Western University,
London, ON N6A 3K7, Canada
Imaging Research Laboratories
Robarts Research Institute,
Western University,
P.O. Box 5015, 100 Perth Drive,
London, ON N6A 5K8, Canada
e-mail: dholdsworth@robarts.ca

1Corresponding author.

Manuscript received January 21, 2014; final manuscript received October 21, 2014; published online January 29, 2015. Assoc. Editor: Guy M. Genin.

J Biomech Eng 137(3), 031005 (Mar 01, 2015) (7 pages) Paper No: BIO-14-1034; doi: 10.1115/1.4028966 History: Received January 21, 2014; Revised October 21, 2014; Online January 29, 2015

High-tibial osteotomy (HTO) is a surgical technique aimed at shifting load away from one tibiofemoral compartment, in order the reduce pain and progression of osteoarthritis (OA). Various implants have been designed to stabilize the osteotomy and previous studies have been focused on determining primary stability (a global measure) that these designs provide. It has been shown that the local mechanical environment, characterized by bone strains and segment micromotion, is important in understanding healing and these data are not currently available. Finite element (FE) modeling was utilized to assess the local mechanical environment provided by three different fixation plate designs: short plate with spacer, long plate with spacer and long plate without spacer. Image-based FE models of the knee were constructed from healthy individuals (N = 5) with normal knee alignment. An HTO gap was virtually added without changing the knee alignment and HTO implants were inserted. Subsequently, the local mechanical environment, defined by bone compressive strain and wedge micromotion, was assessed. Furthermore, implant stresses were calculated. Values were computed under vertical compression in zero-degree knee extension with loads set at 1 and 2 times the subject-specific body weight (1 BW, 2 BW). All studied HTO implant designs provide an environment for successful healing at 1 BW and 2 BW loading. Implant von Mises stresses (99th percentile) were below 60 MPa in all experiments, below the material yield strength and significantly lower in long spacer plates. Volume fraction of high compressive strain ( > 3000 microstrain) was below 5% in all experiments and no significant difference between implants was detected. Maximum vertical micromotion between bone segments was below 200 μm in all experiments and significantly larger in the implant without a tooth. Differences between plate designs generally became apparent only at 2 BW loading. Results suggest that with compressive loading of 2 BW, long spacer plates experience the lowest implant stresses, and spacer plates (long or short) result in smaller wedge micromotion, potentially beneficial for healing. Values are sensitive to subject bone geometry, highlighting the need for subject-specific modeling. This study demonstrates the benefits of using image-based FE modeling and bone theory to fine-tune HTO implant design.

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References

Figures

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Fig. 1

Finite-element model geometry of original knee model (a) including boundary conditions; knee model with simulated HTO with short plate with spacer (b), long plate with spacer (c), and long plate without spacer (d)

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Fig. 2

Stress distribution (von Mises) in short plate with spacer (a), long plate with spacer (b), and long plate without spacer (c) arising from a compressive load of two subject-specific BW (mass = 81.8 kg). Anatomical orientations are indicated with A (anterior) and P (posterior).

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Fig. 3

Mean (box) and standard deviation (whiskers) of 99th percentile von Mises stress arising in the three implant designs at subject-specific compressive loads of one body weight (1 BW) and two body weight (2 BW). *Significant differences between plate designs (p < 0.05).

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Fig. 4

3D rendering of volume elements (dark) in the tibia experiencing compressive strain above 3000 microstrain: without HTO (a); with simulated HTO and short plate with spacer (b), long plate with spacer (c), and long plate without spacer (d) with an applied subject-specific compressive load of 2 BW (mass = 81.8 kg)

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Fig. 5

Mean (box) and standard deviation (whiskers) of volume percentage experiencing compressive strains above 3000 microstrains for original bone and three implant designs at subject-specific compressive loads of 1 BW and 2 BW. *Significant differences between plate designs (p < 0.05).

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Fig. 6

Vertical displacements in the wedge region of model including short plate with spacer (a), long plate with spacer (b), and long plate without spacer (c) arising from a subject-specific compressive load of 2 BW (mass = 81.8 kg). The vertical displacement was utilized to calculate maximum wedge micromotion. Anatomical orientations are indicated with A (anterior) and P (posterior).

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Fig. 7

Mean (box) and standard deviation (whiskers) of maximum vertical wedge micromotion of three implant designs at subject–specific compressive loads of 1 BW and 2 BW. *Significant differences between plate designs (p < 0.05).

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