A 51-year-old woman seeking assistive hearing surgery has become the first patient to successfully undergo robot-assisted cochlear implantation in a clinical trial, reports a new study in the 15 March issue of Science Robotics.
The surgical system involves a robotic drill optimized for arguably the riskiest part of the surgery — drilling a tunnel deep through skull bone into the inner ear. This robot drills with the highest degree of accuracy yet reported for a medical device of its kind, and is equipped with a plethora of safety measures, including an optical camera that can track the robot on a scale of 25 microns — less than the width of a human hair.
“Our procedure is a first step towards a more minimally invasive [surgical] approach. We expect to achieve better and more consistent outcomes for hearing implants when the surgery is conducted with the robot,” said Stefan Weber, professor at the ARTORG Center for Biomedical Engineering Research at the University of Bern and lead author of the study.
Cochlear implantation involves feeding a thin (0.3 to 1 millimeter in diameter) hearing-assistive electrode through a tiny surgically drilled tunnel into the cochlea, the shell-shaped hollow hearing center of the inner ear. Surgeons must bore the tunnel through the cramped space of the middle and inner ear without disrupting nearby facial and taste nerves only micrometers away from the tunnel route.
“Between the two nerves, we have 2.5 millimeters of space, and in this space we need to drill 1.8 millimeters of a hole. So we only have 0.5 to 0.7 millimeters on both sides, and therefore we need to be super, super precise,” Weber explained.
The limits of human abilities are tested while working on this microscopic scale, in which the slightest imprecise movement can cause irreparable damage. As a result, of the 65,000 human-operated cochlear implants inserted globally each year, about 30 to 35% of patients suffer loss of residual hearing in the implanted ear.
Robotics has the potential to provide dexterity and perception surpassing that of a human surgeon. “We see that robots are everywhere today, in production lines, on the streets as autonomous cars, and also in the surgical theaters, and we realize as researchers that robots in the operating rooms today only replicate what humans can do. So, we wanted to investigate whether or not we can make robots do something that human surgeons actually cannot,” said Weber.
Until now, previous studies have worked on individual elements of potential robotic surgical systems. Weber and colleagues have combined these elements into a partially robotic cochlear implantation system.
The procedure begins with a robust computer analysis of the patient’s skull structure, in order to personalize the robotic treatment plan. This blueprint, along with several safety measures woven into the procedure before, during and after the surgery, verifies that the robot is drilling in the correct location.
Most importantly, the robotic portion of the system contains sensors that each confirm the robot is a safe distance away from critical structures and not damaging surrounding tissues. The robot tracks its movements at a scale less than the width of a human hair with an optical camera; pulses radar-like electrical signals through tissues to monitor facial nerves; and measures drill forces transmitted onto the skull.
“To be able to demonstrate that these safety mechanisms are actually efficient, we needed to conduct a lot of different experiments in different preclinical settings. This was quite difficult to solve,” said Weber..
With these tight controls, the robotic drill was able to safely form a tunnel precisely 1.8 millimeters in diameter with an unprecedented accuracy.
However, there is always more to achieve robotically. “The ultimate challenge now is to insert the small implant electrode into the cochlea. The electrode is 0.3-mm at the tip — very wobbly and nearly imperceptible to the human touch. Surgeons have difficulty feeling whether the electrode winds up in the correct spot, in the cochlea,” said Weber.
Notably, his team has demonstrated their system’s capability to perform this last part of the operation, through a robotic mechanism that still requires fine-tuning.
This is just one of the many next steps Weber and colleagues are working on in order to improve their robotic surgical system. “Our clinical trial is ongoing and being tested by more patients. We are also planning multicentric trials, and devising other applications — other implants, drug delivery — that our robotic system can be used for.”
Marco Caversaccio, professor at Inselspital at Bern University Hospital and study co-author, raised another crucial factor necessary for advancing robotic surgery. “Today, what is very important is that you also trust new technology — you have to say, ‘it is not the decision of the robot that makes the hole, it's my decision.’ And this is very important.”
The patient in the clinical trial was discharged from the hospital one day after the operation. She is participating in ongoing evaluation of her implant for the next six months.