Technical accuracy of the stereotactic minimally invasive „RoboJig” system for CI surgery.

Introduction: The essential aspect of the CI surgery is the placement of the CI electrode into the cochlea. However, the main part of the conventional surgical procedure is dealing with the approach to the cochlea. Reducing the approach to a slim tunnel, drilled by high accurate surgical instruments based on temporal bone imaging would reduce the vast extent of the conventional surgical approach. We develop currently a mini-stereotactic frame to hit the cochlea by drilling a tunnel in the mastoid through the facial recess, called RoboJig. The success of the system is mainly dependent its accuracy. We investigated how accurate the target point needs to be reached and how accurate the RoboJig system may be under lab conditions. Methods: Relevant anatomical structures for the CI surgery approach were segmented in eight 3D histological data sets of human temporal bone specimens. Different straight trajectories from the surface of the mastoid passing through the facial recess and entering the cochlea were planned in this virtual environment. A circular region was defined indicating proper places for Cochleostomy To determine the technical accuracy of the system, 20 RoboJig guiding platforms with different trajectories were fabricated and the position and orientation of an inserted drill guide were measured in lab, using a portable coordinate measuring machine. Results: On average the suitable target region was 1.56mm ± 0.11 mm in diameter leading to a mean safety margin of 0.28 mm if the cochleostomy has a diameter of 1.0 mm. On the other side, positioning accuracy was 0.11 mm ± 0.04 mm. Conclusions: Based on planning the surgical root for the straight approach to the cochlea in virtual histological dataset, the RoboJig system seems to be accurate enough for minimally invasive cochlear implantation surgery. However, additional error sources are expected if the drilling is performed in the inhomogeneous bone of the mastoid. [ABSTRACT FROM AUTHOR]