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Technical Briefs

A Modified Footplate for the Kerrison Rongeur

[+] Author and Article Information
Alim P. Mitha

Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA; Department of Neurosurgery, Massachusetts General Hospital, Boston, MA 02114

Mohamed S. Ahmad, Sarah J. Cohen, Janet S. Lieberman, Martin R. Udengaard, Alexander H. Slocum

Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139

Jean-Valery C. E. Coumans1

Department of Neurosurgery, Massachusetts General Hospital, Boston, MA 02114jcoumans@partners.org

1

Corresponding author.

J. Med. Devices 4(1), 014502 (Jan 07, 2010) (4 pages) doi:10.1115/1.4000594 History: Received January 13, 2008; Revised October 15, 2009; Published January 07, 2010; Online January 07, 2010

Use of the Kerrison rongeur for bone removal in spinal surgery is associated with dural tears and cerebrospinal fluid (CSF) leaks. We report a modification of the Kerrison rongeur footplate designed to reduce the risk of dural tears. A novel footplate was designed by incorporating the following parameters: (1) tapering the footplate to deflect soft tissue downward during positioning of the rongeur underneath the bone, and (2) making the footplate longer and wider than the cutting element to prevent soft tissue from entering into the cutting surface. Stereolithography models of the modified footplate were made and tested in a cadaver. A stainless steel modified footplate was then incorporated into an existing Kerrison rongeur as a working prototype, and tested in 20 laminectomy cases to clinically validate its design. The modified footplate prevented soft tissue from entering the cutting surface of the Kerrison rongeur in the manner intended by its design. No dural tears or CSF leaks were encountered in any instance. Potential soft tissue compression caused by an increase in footplate dimensions was not a significant issue in the rongeur size tested. This modification, however, might not be practical in rongeurs larger than 3 mm. The risk of dural tears and cerebrospinal fluid leaks in spinal surgery may be reduced by this footplate modification of the Kerrison rongeur. Soft tissue compression may limit the incorporation of this modification to rongeurs of 3 mm or smaller. The promising results warrant further tests with a wider range of sizes.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

A novel footplate design was created for the Kerrison rongeur that features a tapered bottom as well as a top surface that is wider and longer than the cutting shaft. This geometry was intended to deflect surrounding soft tissue from the cutting area: (a) angled and (b) side views

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Figure 2

A model of the modified footplate was created using stereolithography (SLA) as a snap-on addition to an existing Kerrison rongeur. Here, the model (1 mm of overhang) is being tested in a lamb cadaver spine to assess for potential risks and benefits prior to intraoperative use. The footplate design allows for clearance of dura away from the cutting surface.

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Figure 3

A prototype of the modified Kerrison rongeur was made by microwelding an addition of surgical grade stainless steel onto an existing Kerrison rongeur: (a) side view showing tapered footplate; (b) front view showing flange; (c) top view showing the wider footplate dimensions relative to the shaft; and (d) top view with instrument in occlusion. The scale bars correspond to the area of the image in focus.

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Figure 4

Results of a finite element analysis comparing stresses in the existing footplate (a) with the modified footplate, and (b) as the modified footplate is approximately 30% wider at the area of peak stress (the corner between the footplate and the shaft), the peak stress decreases by approximately 30%. This analysis assumed a force on the footplate from the slider of 100 N.

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