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Biomechanical evaluation of a tool-less external fixator
  1. Diagarajen Carpanen1,
  2. S D Masouros1 and
  3. D J Stinner1,2
  1. 1 Department of Bioengineering, Imperial College London, London, UK
  2. 2 Department of Orthopaedics and Rehabilitation, Vanderbilt University Medical Center, Nashville, Tennessee, USA
  1. Correspondence to Dr S D Masouros, Department of Bioengineering, Imperial College London, London SW7 2AZ, UK; s.masouros04{at}


Introduction Current external fixator systems used by the US and UK military for stabilising extremity fractures require specialised tools to build a construct. The goal of obtaining and maintaining limb length and alignment is not achieved if these tools are misplaced. An alternative, tool-less system is currently available, namely the Dolphix Temporary Fixation System. The aim of this study was to compare the stiffness of the Dolphix system with the existing Hoffmann III system.

Methods Three Hoffmann III and three Dolphix constructs were assembled on a bone (tibia) surrogate. A 30 mm fracture gap was created to simulate a comminuted proximal tibia or distal femur fracture. The constructs were then tested in cyclic axial compression once daily for 3 consecutive days.

Results The length and alignment of the surrogate limb was restored following each testing cycle with both external fixation systems. The stiffness of the constructs was maintained throughout each sequential test, with the Dolphix exhibiting 54% the stiffness of the Hoffmann III construct.

Conclusion Given the Dolphix’s performance in mechanical testing and the unique advantage of having a tool-less manual locking clamp mechanism, this tool-less system should be considered for use in the mobile austere environment.

  • adult orthopaedics
  • limb reconstruction
  • trauma management

Data availability statement

Data are available upon reasonable request. Please email the corresponding author.

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Data availability statement

Data are available upon reasonable request. Please email the corresponding author.

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  • Contributors DJS and SDM conceived the study. DC and DJS collected and analysed the data. SDM reviewed the data analysis. DC wrote the draft manuscript, and all authors read, edited and approved the final manuscript.

  • Funding The main part of this work was conducted in the Royal British Legion Centre for Blast Injury Studies at Imperial College London; therefore, the financial support of the Royal British Legion is gratefully acknowledged.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.