In a recent paper in Science Robotics, a multi-disciplinary team of engineers and surgeons from the University of Bern in Switzerland described their experience of developing and clinically translating a surgical robot to access the cochlea for cochlear implant (CI) surgery (Sci Robot. 2017; 2:eaal4916 http://bit.ly/2w5Z6Ho). The drill attached to their custom-developed, multi-articulated arm robot was optically tracked, as was the patient, allowing the robot to accurately guide the drill through the facial recess to the cochlea. To date, the team has used this system on four patients, demonstrating its clinical feasibility and plans on extending the robot's capabilities to include cochleostomy and electrode array insertion.
While some have expressed safety and accuracy concerns about the trending shift from manual to robot-assisted interventions, I counter: What took us so long? In virtually every field outside of medicine, robotic automation is a no-brainer when repetitive, manual tasks require high precision, e.g., assembling cars. However, with an infinitely more expensive substrate—that is, a human patient—our current standard of care remains manual despite the known limits of human operators and suboptimal outcomes with electrode placement.
While highly trained and talented, surgeons are human. The smallest force that humans can reliably appreciate is approximately 20 millinewtons (mN), which is about the force associated with holding a paperclip with your fingertips. During CI surgery, surgeons are supposed to “…insert [the electrode] until resistance is met,” as noted in a manufacturer's surgical manual. Considering that rupturing the basilar membrane requires a force of 30 mN, surgeons may not be able to reliably feel when intracochlear damage occurs.
The limits of human abilities may be better illustrated by the current outcomes of manual CI electrode placement. At least two groups have reported cases of tip fold-over occurring in about two percent of Cls (Otol Neurotol. 2012;33:169 http://bit.ly/2w5ZNR0; Otol Neurotol. 2017;38:199 http://bit.ly/2vFccM9). At least three groups have reported that translocation of electrode arrays from scala tympani to scala vestibuli happens approximately one-third of time when using pre-curved electrodes that are threaded off stylets during insertion (Otol Neurotol. 2005;26:34 http://bit.ly/2w65y1g; Otol Neurotol. 2008;29:920 http://bit.ly/2w6d3oH; Otol Neurotol. 2016;37:1032 http://bit.ly/2w6pbX8). Why do these incidents happen? Human operators are blindly inserting universal-sized electrodes into an organ—the cochlea—that varies in size between individuals (the length of human cochlear ducts ranges from 25-35 mm; Am J Anat. 1938;62:291) using tools—their hands—that cannot likely sense when damage occurs. On the other hand, robots, such as that of the Bern group, have the advantage of x-ray vision for image-guided surgery, and could be programmed to perform patient-specific insertions while monitoring force and position.
Making robotic technology even more compelling is the overwhelming need for CIs—a demand that current or future manual models are unlikely to satisfy. CI manufacturers report that about 700,000 CI surgeries have been performed worldwide. The World Health Organization, however, estimates that the global need for CI now exceeds 11 million (Otol Neurotol. 2017;38:786 http://bit.ly/2w6c6g6). It is doubtful that each CI surgeon in the world can work 10 times harder to try to meet this need. Training programs tend to offset retiring physicians, and any attempt to expand the workforce would take decades. The only ways to solve this supply and demand mismatch is through technological innovations, such as robotics and simplified surgical approaches, and/or other advances that obviate the need for CIs (e.g., hair cell regrowth).
Whether the Bern robot becomes the panacea for CI surgery remains to be seen. Keep in mind that the technological marvel of CI was introduced with wide skepticism just over 40 years ago. And, while documentation of improved outcomes (e.g., more consistent final electrode location in scala tympani, better audiological outcomes, shorter operative times, etc.) will be necessary before widespread adoption of robotics for CI surgery, hearing health professionals need to remain open to the next breakthroughs providing our patients with the best treatment options.