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Research Papers

A Compact, Bone-Attached Robot for Mastoidectomy

[+] Author and Article Information
Neal P. Dillon

Department of Mechanical Engineering,
Vanderbilt University,
2301 Vanderbilt Place,
PMB 351592,
Nashville, TN 37235
e-mail: neal.p.dillon@vanderbilt.edu

Ramya Balachandran

Department of Otolaryngology,
Vanderbilt University Medical Center,
1215 21st Avenue South,
MCE 10450,
Nashville, TN 37232
e-mail: ramya.balachandran@vanderbilt.edu

J. Michael Fitzpatrick

Department of Electrical Engineering and
Computer Science,
Vanderbilt University,
2301 Vanderbilt Place,
PMB 351679,
Nashville, TN 37235
e-mail: j.michael.fitzpatrick@vanderbilt.edu

Michael A. Siebold

Department of Electrical Engineering and
Computer Science,
Vanderbilt University,
2301 Vanderbilt Place,
PMB 351679,
Nashville, TN 37235
e-mail: michael.a.siebold@vanderbilt.edu

Robert F. Labadie

Department of Otolaryngology,
Vanderbilt University Medical Center,
1215 21st Avenue South,
MCE 10450,
Nashville, TN 37232
e-mail: robert.labadie@vanderbilt.edu

George B. Wanna

Department of Otolaryngology,
Vanderbilt University Medical Center,
1215 21st Avenue South,
MCE 10450,
Nashville, TN 37232
e-mail: george.wanna@vanderbilt.edu

Thomas J. Withrow

Department of Mechanical Engineering,
Vanderbilt University,
2301 Vanderbilt Place,
PMB 351592,
Nashville, TN 37235
e-mail: thomas.j.withrow@vanderbilt.edu

Robert J. Webster, III

Department of Mechanical Engineering,
Vanderbilt University,
2301 Vanderbilt Place,
PMB 351592,
Nashville, TN 37235
e-mail: robert.webster@vanderbilt.edu

1Corresponding author.

Manuscript received November 21, 2014; final manuscript received March 10, 2015; published online July 16, 2015. Assoc. Editor: Lewis Franklin Bost.

J. Med. Devices 9(3), 031003 (Sep 01, 2015) (7 pages) Paper No: MED-14-1274; doi: 10.1115/1.4030083 History: Received November 21, 2014; Revised March 10, 2015; Online July 16, 2015

Otologic surgery often involves a mastoidectomy, which is the removal of a portion of the mastoid region of the temporal bone, to safely access the middle and inner ear. The surgery is challenging because many critical structures are embedded within the bone, making them difficult to see and requiring a high level of accuracy with the surgical dissection instrument, a high-speed drill. We propose to automate the mastoidectomy portion of the surgery using a compact, bone-attached robot. The system described in this paper is a milling robot with four degrees-of-freedom (DOF) that is fixed to the patient during surgery using a rigid positioning frame screwed into the surface of the bone. The target volume to be removed is manually identified by the surgeon pre-operatively in a computed tomography (CT) scan and converted to a milling path for the robot. The surgeon attaches the robot to the patient in the operating room and monitors the procedure. Several design considerations are discussed in the paper as well as the proposed surgical workflow. The mean targeting error of the system in free space was measured to be 0.5 mm or less at vital structures. Four mastoidectomies were then performed in cadaveric temporal bones, and the error at the edges of the target volume was measured by registering a postoperative computed tomography (CT) to the pre-operative CT. The mean error along the border of the milled cavity was 0.38 mm, and all critical anatomical structures were preserved.

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Figures

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Fig. 1

Mastoid region of the temporal bone and photograph from surgical case showing the region after the target bone has been removed with several key anatomical structures identified

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Fig. 2

Planning and workflow of surgical procedure

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Fig. 3

Workspace analysis for the design of the robot. Drilled volume from one of the specimens is shown here with an example of safe and unsafe drill angles to reach a target location. At a safe drill angle, the shaft does not cross the boundary of the target volume except at the lateral surface. An unsafe drill angle causes the shaft to touch untargeted bone and/or other anatomy. The required angular workspace was calculated based on the range of angles needed to reach each point safely.

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Fig. 4

(a) Surgical robotic system includes the robot that holds the surgical drill and mounts on the test specimen via the PPF, the surgical drill control unit and foot pedal for drill speed control, a control hand piece for adjusting robot motion and pausing/stopping the procedure, and the control electronics and computer/monitor, (b) close-up of the robot and PPF, and (c) Gripper mechanism used to attach robot to spheres on PPF

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Fig. 5

(a) Illustration of the use of dilation to accommodate the finite size of the drill bit. Input targeted region is the combination of R2, R3, and R4. Black is the forbidden region, R1. Output targeted region, R3, is light gray. The circular disk centered on P1 represents the structuring element during preprocessing; the disk at P2 represents the drill bit during ablation; and P3 illustrates the super-voxel (hatched square). R2 represents target voxels that will be removed by the edge of the drill. The white regions, R4, are unreachable because of the bluntness of the bit. (b) Two-dimensional illustration of how the super-voxel approach improves the efficiency of the drilling process. The gray cells form the super-voxel within the drill bit (shaded circle) centered at the cross. When the drill bit is active at this location, all voxels within the super-voxel will be considered as hit and removed from the list of remaining target voxels. The next location for the center of the drill bit is the center of the nearest voxel outside the super-voxel, shown as the black cross. The cutting depth is the distance between the two crosses (length of the dashed line).

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Fig. 6

Experimental setup for free space accuracy evaluation. The acrylic phantom contains attachment points for the robot on top and validation spheres for registering the experimental measurements to the CT target points on the bottom.

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Fig. 7

Temporal bone specimen after robotic mastoidectomy

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Fig. 8

Surface error for a cadaver bone. The different colors along the surface represent the error between target and actual milled volumes. A negative error value indicates that the surface of the actual milled volume at that location was inside the planned volume.

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