Percutaneous cochlear implant drilling via customized frames: an in vitro study

Abstract

Objective: Percutaneous cochlear implantation (PCI) surgery uses patient-specific customized microstereotactic frames to achieve a single drill-pass from the lateral skull to the cochlea, avoiding vital anatomy. We demonstrate the use of a specific microstereotactic frame, called a "microtable," to perform PCI surgery on cadaveric temporal bone specimens.

Study design: Feasibility study using cadaveric temporal bones.

Subjects and methods: PCI drilling was performed on six cadaveric temporal bone specimens. The main steps involved were 1) placing three bone-implanted markers surrounding the ear, 2) obtaining a CT scan, 3) planning a safe surgical path to the cochlea avoiding vital anatomy, 4) constructing a microstereotactic frame to constrain the drill to the planned path, and 5) affixing the frame to the markers and using it to drill to the cochlea. The specimens were CT scanned after drilling to show the achieved path. Deviation of the drilled path from the desired path was computed, and the closest distance of the mid-axis of the drilled path from critical structures was measured.

Results: In all six specimens, we drilled successfully to the cochlea, preserving the facial nerve and ossicles. In four of six specimens, the chorda tympani was preserved, and in two of six specimens, it was sacrificed. The mean +/- standard deviation error at the target was found to be 0.31 +/- 0.10 mm. The closest distances of the mid-axis of the drilled path to structures were 1.28 +/- 0.17 mm to the facial nerve, 1.31 +/- 0.36 mm to the chorda tympani, and 1.59 +/- 0.43 mm to the ossicles.

Conclusion: In a cadaveric model, PCI drilling is safe and effective.

Figure 1. Clinical validation of the PCI technique using a customized microstereotactic frame

(a) Starfix platform. (b) Microtable.

Figure 1. Clinical validation of the PCI technique using a customized microstereotactic frame

(a) Starfix platform. (b) Microtable.

Figure 2. Microtable design

The tabletop has three holes for legs that mount on markers and a targeting hole for the trajectory.

Figure 3. Drill press system

The linear guide system controls the advancement of the drill, and the drill bushing adaptor controls the movement of the drill bit.

Figure 4. Trajectory planning

Significant structures are automatically segmented, and a drill trajectory that targets the scala tympani and avoids the facial nerve is determined.

Figure 5

Locations of the three spherical fiducial markers.

Figure 6

Microtable and drill press assembly attached to a cadaveric temporal bone specimen for PCI drilling.

Figure 7. Post-operative CT scan with the drill bit in the drilled hole

The dotted line shows the desired trajectory.