A Biomechanical Comparison of Three Hybrid Linear-Circular External Fixator Constructs

Authors

  • Caleb C Hudson DVM, MS,

    Corresponding author
    1. Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL
    • Comparative Orthopaedics and Biomechanics Laboratory, University of Florida, Gainesville, FL
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  • Daniel D Lewis DVM, Diplomate ACVS,

    1. Comparative Orthopaedics and Biomechanics Laboratory, University of Florida, Gainesville, FL
    2. Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL
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  • Alan R Cross DVM, Diplomate ACVS,

    1. Georgia Veterinary Specialists, Atlanta, GA
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  • Nicholas J Dunbar BSc,

    1. Department of Mechanical and Aerospace Engineering, College of Engineering, University of Florida, Gainesville, FL
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  • MaryBeth Horodyski EdD, ATC, LAT,

    1. Comparative Orthopaedics and Biomechanics Laboratory, University of Florida, Gainesville, FL
    2. Department of Orthopaedics and Rehabilitation, College of Medicine, University of Florida, Gainesville, FL
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  • Scott A Banks PhD, MS,

    1. Department of Mechanical and Aerospace Engineering, College of Engineering, University of Florida, Gainesville, FL
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  • Antonio Pozzi DMV, MS, Diplomate ACVS

    1. Comparative Orthopaedics and Biomechanics Laboratory, University of Florida, Gainesville, FL
    2. Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL
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  • This project was performed in the Comparative Orthopaedics and Biomechanics Laboratory at the University of Florida, College of Veterinary Medicine.

  • Part of the material in this article was presented at the 2010 Veterinary Orthopedic Society Meeting in Breckenridge, CO and at the 2011 ACVS Veterinary Symposium in Chicago, IL.

Corresponding Author

Caleb Hudson, DVM, MS, Department of Small Animal Clinical Sciences, College of Veterinary Medicine, 2015 SW 16th Ave, Gainesville, FL 32610

E-mail: hudsonc@ufl.edu

Abstract

Objective

To evaluate the stiffness, displacement, ring deformation and bone model motion of 3 configuations of linear-circular hybrid fixator constructs loaded in axial compression, craniocaudal and mediolateral bending, and torsion.

Study Design

Biomechanical evaluation.

Sample Population

Three hybrid construct configurations with 8 replicates/configuration.

Methods

Construct Ia used a single, 84 mm, incomplete ring and 2 tensioned olive wires to stabilize 1 bone segment and a primary hybrid rod with 3 fixation pins to stabilize the other bone segment. Constructs Iad and Ib were similar to Ia with the addition of a secondary diagonal hybrid rod. Construct Ib had a fixation pin inserted orthogonally from the diagonal rod. Constructs were loaded for 10 cycles in each mode of loading using a materials testing machine. Ring deformation was assessed by obtaining serial ring measurements. Bone model motion at the fracture gap as a result of loading was also calculated.

Results

Axial compression: constructs Iad and Ib were significantly stiffer than construct Ia. Craniocaudal bending: Construct Ib was significantly stiffer than construct Ia. Mediolateral bending: there were no significant differences between constructs. Torsion: Construct Ib was significantly stiffer than constructs Ia and Iad. Permanent ring deformation did not occur. Bone model translational motion decreased in constructs Iad and Ib compared to construct Ia.

Conclusions

Addition of a secondary hybrid rod as well as biplanar fixation pin placement improved construct stiffness in several loading modes.

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