Design Innovation Paper

A Proximally-Adjustable Variable Length Intramedullary Nail: Ex Vivo Quasi-Static and Cyclic Loading Evaluation

[+] Author and Article Information
Mark J. Hedgeland

Department of Mechanical and Aeronautical Engineering,
Clarkson University,
8 Clarkson Avenue,
Box 5725,
Potsdam, NY 13699
e-mail: hedgelmj@clarkson.edu

Alexander Martin Clark, Jr.

Department of Orthopaedic Surgery,
Sharon Hospital,
50 Hospital Hill Road,
Sharon, CT 06069
e-mail: drmartyclark@yahoo.com

Mario J. Ciani

Department of Occupational Therapy,
Clarkson University,
8 Clarkson Avenue,
Box 5882,
Potsdam, NY 13699
e-mail: mciani@clarkson.edu

Arthur J. Michalek

Department of Mechanical and Aeronautical Engineering,
Clarkson University,
8 Clarkson Avenue,
Box 5725,
Potsdam, NY 13699
e-mail: ajmichal@clarkson.edu

Laurel Kuxhaus

Department of Mechanical and Aeronautical Engineering,
Clarkson University,
8 Clarkson Avenue,
Box 5725,
Potsdam, NY 13699
e-mail: lkuxhaus@clarkson.edu

1Corresponding author.

Manuscript received March 24, 2017; final manuscript received June 20, 2017; published online August 16, 2017. Assoc. Editor: Rita M. Patterson.

J. Med. Devices 11(4), 045001 (Aug 16, 2017) (7 pages) Paper No: MED-17-1193; doi: 10.1115/1.4037260 History: Received March 24, 2017; Revised June 20, 2017

An adjustable-length intramedullary (IM) nail may reduce both complications secondary to fracture fixation and manufacturing costs. We hypothesized that our novel nail would have suitable mechanical performance. To test this hypothesis, we manufactured three prototypes and evaluated them in quasi-static axial compression and torsion and quasi-static four-point bending. Prototypes were dynamically evaluated in both cyclic axial loading and four-point bending and torsion-to-failure. The prototypes exceeded expectations; they were comparable in both quasi-static axial stiffness (1.41 ± 0.37 N/m in cervine tibiae and 2.30 ± 0.63 in cadaver tibiae) and torsional stiffness (1.05 ± 0.26 N·m/deg in cervine tibiae) to currently used nails. The quasi-static four-point bending stiffness was 80.11 ± 09.360, greater than reported for currently used nails. A length-variance analysis indicates that moderate changes in length do not unacceptably alter bone-implant axial stiffness. After 103,000 cycles of axial loading, the prototype failed at the locking screws, comparable to locking screw failures seen clinically. The prototypes survived 1,000,000 cycles of four-point bend cyclic loading, as indicated by a consistent phase angle throughout cyclic loading. The torsion-to-failure test suggests that the prototype has adequate resistance to applied torques that might occur during the healing process. Together, these results suggest that our novel IM nail performs sufficiently well to merit further development. If brought to market, this adjustable-length IM nail could reduce both patient complications and healthcare costs.

Copyright © 2017 by ASME
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Grahic Jump Location
Fig. 1

Adjustable-length IM nail prototypes, in comparison to a Stryker T2 tibial nail. Key features are identified. The inset shows the nut-and-set-screw locking mechanism.

Grahic Jump Location
Fig. 2

Summary of methods used. Prototypes were evaluated quasi-statically in (a) axial, (b) torsional, and (c) four-point bending. Dynamic evaluation included (d) bending and (e) axial cyclic loading. One specimen was loaded to failure in torsion; an example torque–angle plot is shown (f).

Grahic Jump Location
Fig. 3

Quasi-static stiffness results for the current prototype, compared to a previous similar prototype [7], a commercially available nail, and human tibiae, as reported in Refs. [1419]

Grahic Jump Location
Fig. 4

The results of the optimization of axial and torsional stiffness are shown overlaid here. The area surrounding the data points shown indicates the thread overlap and tibia length combinations which would produce a nail/tibia construct which has both axial and torsional stiffnesses within one standard deviation of that of the Synthes Expert Nail [1419].



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