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Research Papers

A Novel Halo Orthosis to Reduce Pin Loosening

[+] Author and Article Information
G. Joshua Karnes, Brittiney N. Hofmann

 Rose-Hulman Institute of Technology, 5500 Wabash Avenue, CM153 Terre Haute, IN 47803

Richard E. Stamper

 Rose-Hulman Institute of Technology, 5500 Wabash Avenue, CM153 Terre Haute, IN 47803richard.stamper@rose-hulman.edu

J. Med. Devices 2(2), 021004 (Jun 25, 2008) (4 pages) doi:10.1115/1.2931550 History: Received November 20, 2007; Revised March 27, 2008; Published June 25, 2008

Pin loosening is a frequent complication associated with the use of halo orthoses. Efforts to reduce pin loosening incidence include increasing the number of halo pins, increasing the torque specification, and proactively retightening the halo pins. Although these approaches lower pin loosening incidence rates, none addresses the cause of pin loosening, which is the inability of current halo ring designs to accommodate changes in geometry of the skull. A novel four-pin adaptive halo ring is introduced that can accommodate changes in geometry of the skull and provide a nearly constant pin force. To quantify pin loosening in a halo ring, tests were performed using a fixture that was capable of simulating the changes in skull geometry that are responsible for pin loosening. Both the four-pin adaptive halo and a conventional halo were tested. After 1.1mm of radial recession of the skull at the pin site, the average halo pin force in the conventional halo decreased by 78% while the average halo pin force in the four-pin adaptive halo decreased by 12%. In addition, the four-pin adaptive halo had significantly less variation in initial halo pin force (p-value <0.0001) than that of the four-pin adaptive halo.

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Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Typical halo orthosis system

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Figure 2

Exploded and unexploded view of four-pin adaptive halo

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Figure 3

The adaptive halo in its relaxed (left) and loaded (right) configurations

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Figure 4

Simulated skull fixture with four-pin adaptive halo

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Figure 5

Section view of a halo pin with internally placed strain gauge

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Figure 6

Bremer Halo Crown individual pin forces of one trial as a function of radial recession

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Figure 7

Four-pin adaptive halo individual pin force of one trial as a function of radial recession

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Figure 8

Bremer Halo Crown and four-pin adaptive halo average pin force and standard deviation for all trials as a function of radial recession

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