Instrument flight to the inner ear

Abstract

Surgical robot systems can work beyond the limits of human perception, dexterity and scale making them inherently suitable for use in microsurgical procedures. However, despite extensive research, image-guided robotics applications for microsurgery have seen limited introduction into clinical care to date. Among others, challenges are geometric scale and haptic resolution at which the surgeon cannot sufficiently control a device outside the range of human faculties. Mechanisms are required to ascertain redundant control on process variables that ensure safety of the device, much like instrument-flight in avionics. Cochlear implantation surgery is a microsurgical procedure, in which specific tasks are at sub-millimetric scale and exceed reliable visuo-tactile feedback. Cochlear implantation is subject to intra- and inter-operative variations, leading to potentially inconsistent clinical and audiological outcomes for patients. The concept of robotic cochlear implantation aims to increase consistency of surgical outcomes such as preservation of residual hearing and reduce invasiveness of the procedure. We report successful image-guided, robotic CI in human. The robotic treatment model encompasses: computer-assisted surgery planning, precision stereotactic image-guidance, in-situ assessment of tissue properties and multipolar neuromonitoring (NM), all based on in vitro, in vivo and pilot data. The model is expandable to integrate additional robotic functionalities such as cochlear access and electrode insertion. Our results demonstrate the feasibility and possibilities of using robotic technology for microsurgery on the lateral skull base. It has the potential for benefit in other microsurgical domains for which there is no task-oriented, robotic technology available at present.

Figure 1. Robotic cochlea implantation RCI.

(A) Elements of RCI: (i) computer-based patient-specific intervention planning, (ii) RMA, (iii) RIA, and (iv) 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).

Figure 2. Visual representation of the treatment model for RMA.

Procedural elements and risk mitigation activities of an RCI plan.

Figure 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.

Figure 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.

Figure 5. System overview.

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

Figure 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.

Figure 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 drilling process).

Figure 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 (Anode_i), 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.