Robot-Assisted Surgery at the Lateral Skull Base

Introduction: Recently there has been a comeback of improved small-size robotic devices for intraoperative use, especially for skull base procedures. The current state of research is that experimental systems can perform highly precise boreholes, for example, for a cochlear implant operation. The necessary surgical accuracy for the ideal opening of the cochlea is 0.3 to 0.5 mm. Here we present the first results of our work group for performing a mechatronically accomplished drilling of the mastoid and cochleostomy.

Material and Method: The small industry robot KR3 (KUKA, Germany) with 6 degrees of freedom was armed with a conventional medical milling burr. We used an optoelectronic navigation system (BrainLAB, Germany) which was equipped with the interface software VVLink for connecting the navigation system to the robot. For improving the accuracy of the navigation systems the underlying imaging was acquired with a flat-panel-based volume computer tomograph (fp-VCT). The segmentation of the functionally relevant structures of the temporal bone (cochlea, facial nerve, chorda tympani, sigmoid sinus, and semicircular canals) in the imaging was done by the software iPlan2.5 (BrainLAB). Afterward a trajectory was planned respecting all risk structures with a safety distance of at least 1.5 mm. The entry point of the trajectory was positioned retroauricularly with the target in the basal turn of the cochlea. The robot drilled a hole behind the external ear canal from the skull surface to the cochlea. Postoperatively, conventional drilling of the mastoid with posterior tympanotomy and exposure of the facial recess was performed to evaluate the resulting position of the minimally invasive cochleostomy. This procedure was carried out in five human temporal bone specimens.

Results: The surgery time was about 10 minutes. The postoperative fp-VCT imaging showed that the planned trajectory was bored along the planned trajectory without harming the at-risk structures. These findings were confirmed by postinterventional anatomical findings.

Discussion: We used a navigation-controlled robot for performing a minimally invasive procedure to the middle ear and a highly precise cochleostomy. The accuracy of the navigation technology could be improved by a modern fp-VCT device in such a manner that submillimetric precision results could be achieved.