Research Papers

Design of a Dynamic External Finger Fixator

[+] Author and Article Information
May M. Youssef

School of Mechanical Engineering,
University of Birmingham,
Birmingham B15 2TT, UK
e-mail: mmy179@bham.ac.uk

Duncan E. T. Shepherd

School of Mechanical Engineering,
University of Birmingham,
Birmingham B15 2TT, UK
e-mail: d.e.shepherd@bham.ac.uk

O. Garth Titley

Queen Elizabeth Hospital,
Birmingham B15 2TH, UK
e-mail: Garth.Titley@uhb.nhs.uk

Manuscript received October 28, 2015; final manuscript received March 14, 2016; published online August 5, 2016. Assoc. Editor: Rita M. Patterson.

J. Med. Devices 10(4), 041004 (Aug 05, 2016) (6 pages) Paper No: MED-15-1286; doi: 10.1115/1.4033602 History: Received October 28, 2015; Revised March 14, 2016

This paper describes an improved design of an external fixator. The new fixator comprises 13 parts which are assembled together. The proposed device materials consist of polyether ether-ketone (PEEK) and stainless steel 316L. The design was subjected to finite-element analysis, and a working model was manufactured and subjected to cyclic mechanical testing. The finite-element analysis showed that the maximum stress was 242.9 MPa and this was less than the yield strength and the fatigue endurance limits for the selected materials. Mechanical testing showed that testing reached run-out of 170,000 cycles with no cracks or damage visible in the device parts.

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Fig. 1

(a) Assembled compass hinge external fixator, with the individual parts numbered and (b) attached to a patient's finger

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Fig. 2

Assembled design of the new external dynamic protractor hinge fixator

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Fig. 3

Meshed finite-element model of the new fixator with the load 210N and constrains applied at position 1 gear teeth fixed at 15–30 deg. Arrows on teeth and axle indicate the constrains, and arrows on the clamping block indicate the forces.

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Fig. 4

Assembled fixator in two different positions of engagement with the worm gear: (a) position 1 gear teeth fixed at 15–30 deg and (b) position 2 gear teeth fixed at 90–105 deg

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Fig. 5

Working model of the external dynamic protractor hinge fixator that was manufactured using additive-manufacturing processes

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Fig. 6

The setup used for the cyclic bending test of the working model

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Fig. 7

Distribution of von Mises stresses for the model of the new fixator for position 1 gear teeth fixed at 15–30 deg




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