BACKGROUNDA single drilled tunnel from the lateral mastoid cortex to the cochlea via the facial recess is essential for minimally invasive cochlear implant surgery. This study aimed to explore the safety profile of this kind of new image-guided and bi-planar device-assisted surgery procedure in vitro.

METHODSImage-guided minimally invasive cochlear implantations were performed on eight cadaveric temporal bone specimens. The main procedures were: (1) temporal bone specimens were prepared for surgery and fiducial markers were registered. (2) computed tomography (CT) scans were performed for future reference. (3) CT scan images were processed and drill path was planned to minimize cochlear damage. (4) bi-planar device-assisted drilling was performed on the specimens using the registration. (5) surgical safety was evaluated by calculating the deviation between the drill and the planned paths, and by measuring the closest distance between the drilled path and critical anatomic structures.

RESULTSEight cases were operated successfully to the basal turn of the cochlear with intact facial nerves (FNs). The deviations from target points and entrance points were 0.86 mm (0.68-1.00 mm) and 0.44 mm (0.30-0.96 mm), respectively. The angular error between the planned and the drilled trajectory was 1.74° (1.26-2.41°). The mean distance from the edge of the drilled path to the FN and to the external canal was 0.60 mm (0.35-0.83 mm) and 1.60 mm (1.30-2.05 mm), respectively. In five specimens, the chorda tympani nerves were well preserved. In all cases, no injury happened to auditory ossicles.

CONCLUSIONSThis exploratory study demonstrated the safety of the newly developed image-guided minimally invasive cochlear implantation assisted by the bi-planar device and established the operational procedures. Further, more in vitro experiments are needed to improve the system operation and its safety.