In Vitro Mechanical Comparison of Screwed, Bolted, and Novel Interlocking Nail Systems to Buttress Plate Fixation in Torsion and Mediolateral Bending

Authors

  • JENNIFER L. LANSDOWNE DVM, MSc,

    1. Department of Small Animal Clinical Sciences, College of Veterinary Medicine
    2. Orthopedic Biomechanics Laboratories, College of Osteopathic Medicine, Michigan State University, East Lansing, MI
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  • MICHAEL T. SINNOTT MS,

    1. Department of Small Animal Clinical Sciences, College of Veterinary Medicine
    2. Orthopedic Biomechanics Laboratories, College of Osteopathic Medicine, Michigan State University, East Lansing, MI
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  • LOIC M. DÉJARDIN DVM, MS, Diplomate ACVS,

    1. Department of Small Animal Clinical Sciences, College of Veterinary Medicine
    2. Orthopedic Biomechanics Laboratories, College of Osteopathic Medicine, Michigan State University, East Lansing, MI
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  • DENNIS TING DVM,

    1. Department of Small Animal Clinical Sciences, College of Veterinary Medicine
    2. Orthopedic Biomechanics Laboratories, College of Osteopathic Medicine, Michigan State University, East Lansing, MI
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  • ROGER C. HAUT PhD

    1. Department of Small Animal Clinical Sciences, College of Veterinary Medicine
    2. Orthopedic Biomechanics Laboratories, College of Osteopathic Medicine, Michigan State University, East Lansing, MI
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  • Supported by the Michigan State University Companion Animal Fund. Presented in part at the Annual Meeting of the European College of Veterinary Surgeons, Lyon, France, July 2005 and the Annual Meeting of the American College of Veterinary Surgeons, Washington, DC, October 2006.

Address reprint requests to Dr. Déjardin, DVM, MS, Department of Small Animal Clinical Sciences, Michigan State University, East Lansing, MI 48824. E-mail: Dejardin@cvm.msu.edu.

Abstract

Objective— To compare standard interlocking nails (ILN) with a newly designed ILN featuring an angle-stable locking mechanism (ILNn).

Study design— Six experimental groups.

Sample population— Bone models (n=48) treated with 6 and 8 mm nails locked with screws or bolts (ILN6s, ILN8s, ILN6b, ILN8b, respectively), ILNn, and a 3.5 mm broad-DCP (br-DCP); n=4/testing mode.

Methods— Specimens were tested in torsion or 4-point bending. Construct compliance, deformation, and slack were statistically compared (P<.05).

Results— Regardless of testing mode, construct compliance was greater with smaller ILN. Screwed constructs were more compliant than bolted ones, with a significant difference between ILN6s and ILN6b in torsion. Plated constructs were significantly more compliant than the ILNn. Angular deformation was consistently greater with smaller ILN. Screwed ILN constructs sustained ∼2 × the torsional deformation of the bolted ones (∼36° [ILN6s] versus ∼18° [ILN6b]). Comparatively, ILNn constructs had significantly less torsional (∼8°) and bending (∼4°) deformation than other constructs. Whereas standard ILN constructs had slack in both modes, ILNn and br-DCP construct deformations consistently occurred without slack.

Conclusions— Use of bolts rather than screws improved ILN mechanical behavior, but neither locking mechanism completely counteracted torsion and bending forces. Conversely, the ILNn angle-stable locking system eliminated torsional and bending slack, resulting in comparable mechanical performances between ILNn and plated constructs.

Clinical Relevance— The angle-stable locking mechanism of the new ILN eliminates all slack in the system; thus, interfragmentary motion will likely be reduced compared with standard ILN, which may improve the local environment for fracture healing.

Ancillary