Characterization of friction and speed effects and methods for detection of cochlear implant electrode tip fold-over

Perimodiolar electrode arrays for cochlear implant surgery present surgeons with challenges during their insertion into the cochlea. These challenges stem from the inherent flexibility of these arrays and the fragile intracochlear anatomy and has opened opportunities for high precision robotic systems. This paper investigates effects of insertion speed on insertion forces using perimodiolar electrode arrays in human temporal bones and complements previously published results on insertion force and speed relationships when using straight outer-wall electrode arrays. The paper presents a custom-made parallel robot equipped with a high resolution force/moment sensor as an insertion platform. Experimental results using 42 insertions in 8 temporal bones are analyzed and grouped by insertion speed. Our results show a reduction in insertion forces up to insertion speeds of 1 mm/s. The second aspect of this paper is the investigation of the feasibility of using insertion force and speed data to sense conditions predicting the onset of electrode tip fold over, a complication resulting in poor placement of electrode contacts. It is shown that tip folding can be detected by features taken from insertion force data when employing a support vector machine classifier. The capability to detect such errors in a procedure is a critical component to the development of a practical surgical tool.