Clinical assessment of the positioning accuracy of the RoboJig system by comparison with anatomical and surgical constraints

Introduction:

The surgical treatment with a cochlear implant (CI) requires a surgical access to the inner ear (cochlea). High spatial accuracy is essential when performing this approach in minimally invasive fashion which calls for an image-guided surgical assistance device. To assess the clinical usability of our new micro-stereotactic frame, named RoboJig which is currently under development, we investigated both how accurate the target point needs to be reached and how accurate the RoboJig system is able to position surgical tools as e.g. a drill.

Methods:

In eight 3D histological data sets of human temporal bone specimens relevant anatomical structures of the lateral skull base were manually segmented and a virtual drill path was planned simulating the standard facial recess approach. This plan comprised a circular region indicating proper places for opening the inner ear without harming functional structures. On the other side, we fabricated 20 RoboJig guiding platforms with different trajectories and measured the position and orientation of an inserted drill guide using a portable coordinate measuring machine.

Results:

On average the suitable target region was 1.56 mm ± 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 these preliminary findings 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. On the other side, decreasing the size of the cochleostomy will enlarge the safety margin and seems to be feasible with state-of-the-art thin lateral wall electrode arrays.

Publication History

Publication Date:
18 April 2018 (online)