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Design Innovation Paper

A proximally-adjustable variable length intramedullary nail: ex-vivo quasi-static and cyclic loading evaluation

[+] Author and Article Information
Mark Hedgeland

ASME member Clarkson University, Department of Mechanical & Aeronautical Engineering, 8 Clarkson Ave., Box 5725, Potsdam, NY 13699
hedgelmj@clarkson.edu

Alexander Martin Clark

Department of Orthopaedic Surgery, Sharon Hospital, 50 Hospital Hill Rd, Sharon, CT 06069
drmartyclark@yahoo.com

Mario Ciani

Clarkson University, Department of Occupational Therapy, 8 Clarkson Ave., Box 5882, Potsdam, NY 13699
mciani@clarkson.edu

Arthur J Michalek

Clarkson University, Department of Mechanical & Aeronautical Engineering, 8 Clarkson Ave., Box 5725, Potsdam, NY 13699
ajmichal@clarkson.edu

Laurel Kuxhaus

ASME member Clarkson University, Department of Mechanical & Aeronautical Engineering, 8 Clarkson Ave., Box 5725, Potsdam, NY 13699
lkuxhaus@clarkson.edu

1Corresponding author.

ASME doi:10.1115/1.4037260 History: Received March 24, 2017; Revised June 20, 2017

Abstract

An adjustable-length intramedullary 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 4-point bending. Prototypes were dynamically evaluated in both cyclic axial loading and 4-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 Nm/degree in cervine tibiae) to currently-used nails. The quasi-static 4-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 4-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 (c) 2017 by ASME
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