Research Papers

An Articulating Tool for Endoscopic Screw Delivery

[+] Author and Article Information
Joseph E. Petrzelka

 Massachusetts Institute of Technology, 77 Massachusetts Avenue 35-135, Cambridge, MA 02139jepetrz@mit.edu

Manas C. Menon, Clara J. Stefanov-Wagner, Dimitris Chatzigeorgiou, Michelle Lustrino, Alexander H. Slocum

 Massachusetts Institute of Technology, 77 Massachusetts Avenue 35-135, Cambridge, MA 02139

Suresh K. Agarwal

 Boston University, Boston, MA 02139

J. Med. Devices 5(1), 011004 (Feb 17, 2011) (7 pages) doi:10.1115/1.4003435 History: Received May 12, 2010; Revised December 20, 2010; Published February 17, 2011; Online February 17, 2011

This paper describes the development of an articulating endoscopic screw driver that can be used to place screws in osteosynthetic plates during thoracoscopic surgery. The device is small enough to be used with a 12 mm trocar sleeve and transmits sufficient torque to fully secure bone screws. The articulating joint enables correct screw alignment at obtuse angles, up to 60 deg from the tool axis. A novel articulating joint is presented, wherein a flexible shaft both transmits torque and actuates the joint; antagonist force is provided by a superelastic spring. Screws are secured against the driver blade during insertion with a retention mechanism that passively releases the screw once it is securely seated in the bone. The prototype has been fitted with a blade compatible with 2.0 and 2.3 mm self-drilling screws, though a different driver blade or drill bit can be easily attached. Efficacy of the tool has been demonstrated by thoracoscopically securing an osteosynthetic plate to a rib during an animal trial. This tool enables minimally invasive, thoracoscopic rib fixation.

Copyright © 2011 by American Society of Mechanical Engineers
Topics: Torque , Screws , Design
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Figure 1

An endoscopic driver must have an articulating joint to place screws at the correct orientation; the required angle of articulation is positively correlated with the end length of the device. While illustrated here in two dimensions, the additional degree of freedom allows access of multiple fracture sites on different ribs through a single incision.

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Figure 2

Prior screw retainer design; the screw can be either (a) held by a set of retaining and locking sleeves or (b) released by sliding the sleeves away from the screw head (17). This common design is difficult to adapt to endoscopic use because it requires actuation.

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Figure 3

Articulating endoscopic screw driver, shown at maximum degree of articulation

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Figure 4

Novel articulating joint design incorporating actuation via a torque-transmitting flexible shaft and antagonist actuation via a superelastic spring (illustrated at each extreme of articulation). A slot in the housing allows the flexible shaft to move off-center at high degrees of articulation.

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Figure 5

(a) Novel passive screw retention mechanism demonstrating the use of a snap fit to retain the screw to the driver tip. (b) The retainer snaps onto the tool end and snaps around the screw head to firmly retain it. (c) Retainer in the operating position. (d) As the screw fully seats, the retainer is pushed back by the substrate to release the screw.

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Figure 6

External actuation mechanism, incorporating (a) a power drill adapter torque and (b) a lead screw collar (c) to adjust the relative position of the tool body forward, which causes the tip to articulate (d) due to the relative foreshortening of the flexible shaft

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Figure 7

Static torque rating versus outer diameter for stainless steel universal joints, curve shows a best fit to data points collected in a survey of commercially available components

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Figure 8

Model of flexible shaft geometry as a function of articulation angle θ, pivot length L, and pivot offset D

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Figure 9

Schematic illustrating the change in flex shaft arc length between the extremes of articulation, actuation tension in the flex shaft is balanced by an antagonistic beam spring

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Figure 10

Chart of antagonist moment (N m) as a function of articulation angle for NiTi and stainless steel beam springs at a maximum curvature of 72 m−1. The superelastic NiTi provides a larger and more uniform antagonistic moment for uniform response to external stimuli.

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Figure 11

Chart of flex shaft tension (N) as a function of articulation angle, pin shear force and actuation force are of similar magnitude and response

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Figure 12

Cantilever beam snap fits on screw retainer shown in (a) neutral position and (b) snap position. (c) Energy methods are used to analytically relate removal force to the cantilever deflection force and interface friction themselves, functions of cantilever stiffness and deflection.

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Figure 13

(a) Prototype of the endoscopic driver: the articulating joint is actuated by the flex shaft while the remote handle incorporates an adapter to a standard surgical drill. A collar with an integral lead screw allows simple and precise adjustment of articulation. (b) Tool disassembles for cleanout and sterilization.

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Figure 14

The tool successfully articulates from 0 deg (neutral) to 60 deg with continuous resolution, angles of 10–60 deg are illustrated here

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Figure 15

Images from porcine trial: (a) drilling, (b) screw placement using screw retainer, (c) full articulation for drilling, and (d) plate placement via trocar




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