Research ArticleMEDICAL ROBOTS

Instrument flight to the inner ear

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Science Robotics  15 Mar 2017:
Vol. 2, Issue 4, eaal4916
DOI: 10.1126/scirobotics.aal4916
  • Fig. 1 Robotic cochlea implantation RCI.

    (A) Elements of RCI: (i) computer-based patient-specific intervention planning, (ii) RMA, (iii) RIA, and (iii) robotic electrode array insertion. (B) Scale of RCI: A 1.8-mm trajectory to be planned and drilled starting from behind the ear (i), through the mastoid bone (ii) bypassing critical structures at <1-mm proximity and toward the inner ear. Trajectory viewed along its axis (iii) and from the side (iv).

  • Fig. 2 Visual representation of the treatment model for RMA.

    Procedural elements and risk mitigation activities of an RCI plan.

  • Fig. 3 Surgical preparation, robotic drilling, and implant insertion.

    (A) Noninvasive, steady placement of the patient’s head on pressure pads attached to a carbon fiber support structure. Electrodes for neuromonitoring of the facial nerve are attached to facial muscles. (B) The robotic drill accesses the situs through a 20-mm incision. (C) Using an insertion tube, the CI electrode is inserted through the 1.8-mm keyhole into the cochlea.

  • Fig. 4 Confirmation of safe passage and postoperative situation.

    (A) Intraoperative CBCT imaging allows delineation of the trajectory and the facial nerve. A neuroradiologist manually confirms sufficient distance between the trajectory and the facial nerve. (B) Inserted electrode array, excess lead placement, and final implant position as measured in postoperative CT imaging.

  • Fig. 5 System overview.

    Highlighting all relevant robotic, stereotactic, and surgical instrument components.

  • Fig. 6 Planning the intervention.

    The planning software tool allows for general image segmentation (i.e., identification of the fiducial screws, in green), segmentation of anatomy (i.e., facial nerve, in yellow), and parametrization of the general treatment plan.

  • Fig. 7 Pose estimation using drill force and bone density.

    Computation of the trajectory pose using a correlation of bone density (from CT) and drill force (recorded during drill process).

  • Fig. 8 Neuromonitoring of the facial nerve during robotic drilling.

    (A) Optically tracked stimulation probe inserted in the drilled tunnel near the facial nerve before application of an automatic protocol through four channels of the probe. (B) Probe with cathode to anode distances to be di = 2, 4, 7 mm (Anodei), and monopolar stimulation enabled by a far-field needle electrode (superficial to the sternum). (C) After automatic stimulation between 0.2 and 2 mA, EMG responses only appeared at 2 mA and the monopolar configuration, suggesting a safe drilling passage at facial nerve distances above 0.7 mm. (D) Example of electrically elicited EMG signals during drilling, showing amplitude range and polyphasic nature of responses.

  • Table 1 RMA model.

    The model’s elements consist of robotic activities (R), risk mitigation actions (A), and manual activities (M).

    R1Robotic drilling from
    mastoid surface to
    3 mm before the level
    of the facial nerve
    XStart, XEnd
    Drilling interval = 2 mm
    rpm: 1000
    Irrigation: 15 ml/minute
    Guiding: Optical tracking
    Velocity = 0.5 mm/s
    Drill diameter: 2.5 mm
    A1Intraoperative CBCT
    Field of view: 80 × 80 × 80 mm3
    Resolution: 0.156 × 0.156 mm2
    Slice thickness: 0.2 mm
    A2Bone density analysisCandidate trajectories: n = 2000
    Volume of interest: 3 mm ×
    3 mm × 30 mm around
    planned trajectory
    R2Robotic drilling lateral to
    the facial nerve
    XStart, XEnd
    Drilling interval = 0.5 mm
    rpm: 1000
    Irrigation: 15 ml/min
    Guiding: Optical tracking
    Velocity = 0.5 mm/s
    Drill diameter: 1.8 mm
    A3EMG facial nerve
    Measurement points: 5
    Distance between points: 0.5 mm
    Monopolar channels: 1
    Bipolar channels: 3
    Pulse duration: 250 μs
    Intensities per channel: 0.2..2 mA
    I = logarithmic)
    R3Facial nerve to 2 mm
    before the round
    XStart, XEnd
    Drilling interval = 2mm
    rpm: 1000
    Irrigation: 15 ml/min
    Guiding: Optical tracking
    Velocity = 0.5 mm/s
    Drill diameter: 1.8 mm
    R4Cochlea opening
    Guiding: Force feedback
    Bur Ø 1.0 mm
    M5Electrode insertion
    Choice of implant: Flex24 (MED-EL)
    Length of insertion: 360°
  • Table 2 Robotic access plan.

    R, robotic actions; A, risk mitigation actions.

    R1Drilling commenced from the lateral skull surface
    to 3 mm before the facial nerve
    4 min
    A1Effective trajectory pose measurement using drill
    force–to–bone density correlation.
    Sufficient lateral space of the trajectory from
    the facial nerve and the chorda tympani
    was confirmed to be 1.0 and 0.3 mm,
    1 min
    A2Acquisition of intraoperative CT yielded sufficient
    lateral space of the trajectory from the facial
    nerve and the chorda tympani to be 1.0 and
    0.2 mm, respectively
    55 min
    R2Passing at the critical safe distance to both the
    facial nerve (<1.0 mm) and the chorda tympani
    (0.3 mm). Intervals of the robotic drilling were
    shortened (0.5 mm versus 2 mm) to mitigate for
    heat buildup
    3 min
    A3EMG facial nerve monitoring was performed at six
    positions and every 0.5-mm increment in depth.
    At all positions, neuromonitoring yielded a distance
    of the trajectory safe for the facial nerve
    5 × 2 min
    R3Drilling phase R3 commenced 3 mm past the level of
    the facial nerve and concluded 2 mm before the
    planned target location on the cochlea within the
    middle ear cavity
    3 min
  • Table 3 EMG decision table.

    Decisions are based on stimulus threshold values above (0) or below (1) 0.35 mA.

    Electrode configurationEstimated
    distance ranges
    drill to facial
    nerve (mm)
    d = 2 mmd = 4 mmd = 7 mm
    00000.7Continue to drill>95%
    00010.60.7Continue to drill>95%
    00100.40.6Continue to drill<95%
    00110.40.7Continue to drill>95%
    01000.10.4Further assessment required<95%
    01110.10.4Critical to abort>95%
    100 or 10 or 100.1Abort RCI<95%
    110 or 10 or 100.1Abort RCI>95%
  • Supplementary Materials

    Supplementary Material for:

    Instrument flight to the inner ear

    Stefan Weber,* Kate Gavaghan, Wilhelm Wimmer, Tom Williamson, Nicolas Gerber, Juan Anso, Brett Bell, Arne Feldmann, Christoph Rathgeb, Marco Matulic, Manuel Stebinger, Daniel Schneider, Georgios Mantokoudis, Olivier Scheidegger, Franca Wagner, Martin Kompis, Marco Caversaccio

    *Corresponding author. Email:{at}

    Published 15 March 2017, Sci. Robot. 2, eaal4916 (2017)
    DOI: 10.1126/scirobotics.aal4916

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