In this two-part series on robotics and wearable devices, part 1 highlighted the wearable device product category. Part 2 moves the discussion from wearable devices to how robotic surgery is changing the future of surgery. This article discloses five fundamental human factors that must be addressed in the design of any robotic surgical system. And not unlike part 1 on wearable devices, the terms ergonomics and human factors engineering are used interchangeably.
Robotics design is hard work. These complicated surgical platforms are run by a highly trained team of five to seven clinicians, which includes the surgeon, scrubs, circulating nurses, and technicians. Typically, two to three multifunctional micro instruments and a 3D HD camera are controlled by the surgeon through a hand controller interface.
Robotics permit the user the ability to perform tasks with miniaturized electromechanical devices that could never be done with the user's hands. These micro instruments allow for smaller incisions, more finite control at the surgical site, and faster surgeries. These state-of-the-art robotic assistants collectively contribute to quicker recovery times. In robotic surgery, it's all about control. And control starts with the tip of the spear — the human hand, the gateway to good surgery.
The Big Hairy Problem: Mimicking the Human Hand
The surgeon controller interface is one of the toughest design challenges in robotic surgery. This is where the rubber meets the road. Precision and control are the primary objectives in robotic surgery. A robotic surgical tool must be optimized for the three smartest fingers on each hand — the thumb, index, and middle fingers. These three smart fingers are used the most, day in and day out, for fine dexterous precision-based tasks. Several times throughout the day, people routinely use their smartest grips, the “trilateral precision grip” (see Figure 1).
The controller design must allow the surgeon to use their fingers in a natural unencumbered way, but with just enough resistance for the sense of touch without impedance by the design of the controller itself. And the design must accommodate for differences in hand size and strength, from 5th female to 95th male percentiles. This is the toughest part; millimeters matter in getting a synchronous motion that optimizes dexterity and precision while also fitting across the full range of hand sizes. Not only the physical fit of the controllers matter, but also how they behave.
Gain — How Far Do You Turn It Up?
Research on system gain dates back to at least the 1960s, when the focus was on human factors and human performance. Research shows that magnification and gain are interrelated. For example, it is reported in vitreoretinal systems that they require high precision and have used gain ratios as high as 40:1. Experiments to date show that for more traditional robotic surgical systems, gain ratios from 2:1 to 7:6 is an optimal range.
Learning Curves — How Long Does It Take to Learn Robotics?
There are numerous studies citing learning curves comparing expert surgeons to novice medical students or novice volunteers. Clinical studies typically report performance on a specific procedure or task in urology, cardiothoracic, gynecology, or general surgery. Here are the highlights of what is known today about learning curves related to robotics and laparoscopic techniques:
Surgeons performing simple tasks demonstrated rapid learning, performing equally well on laparoscopic and robotic platforms.
The surgeons demonstrated faster learning and peak performance times on the advanced task of tying a suture on the robotic platform.
Surgical performance continued to improve as practice time continued, making the suture tying task faster using a robotic system.
Skilled laparoscopic surgeons performed robotic tasks in less time, both initially and after practice.
Learned laparoscopic tasks transferred to robotic surgeons, in both simple and complex tasks.
Interestingly, the greatest improvements are seen in participants with the least amount of laparoscopic experience. And, learning basic skills to carry out a surgical procedure in both laparoscopic and robotic platforms have steep learning curves, and skills plateau after as few as five to 10 surgeries. But learning is influenced by workload.
Workload — What Are They Thinking?
Workload is a key design factor to consider in robotic surgery. It is the amount of work that an individual must do, or the individual's perception of the amount of work. Humans have limits to the amount of workload they can effectively cope with before it impacts performance. When thinking about workload, it is convenient to dissect it into physical workload and cognitive workload.
Physical workload is measured by how the body interacts with tools or the environment, and the effects of those interactions on the body with regard to posture, repetitive motion, workplace layout, material handling, musculoskeletal stress, and any associated injuries or disorders.
Cognitive workload is about the mental resources a person has available to use and considers the mind, memory, sensory motor response, perception, and stress. Everyone has a fixed cognitive bandwidth that when exceeded reduces performance, judgment, and decision making. Any aspect of a design that requires the surgeon or the scrub for the circulator to think longer than they should consumes valuable mental resources that would be better focused on the surgical procedure itself. Designers must be careful that the design does not block the road of usability.
Here's how workload interacts with surgeon comfort, stress and cognitive loading, and processing:
Laparoscopic surgery demands greater physical workload than general surgery.
Physical workload demands are greater during laparoscopic surgery than robotic surgery.
Lower muscular activation levels have been demonstrated in neck, arms, shoulders, and back while performing robotic surgery than laparoscopic surgery.
Laparoscopic and robotic surgeons show lower physical workload when performing robotic tasks.
First-year residents and expert surgeons alike display lower levels of nervousness while using a robotic surgical system.
Stress and concentration are higher for laparoscopic surgical tasks than for robotic tasks as measured by skin conductance, eye blinks, and questionnaires.
The incidence of occupational symptoms or injuries in laparoscopic surgeons was reported to be as high as 87 percent.
Stress — The Wild Card
Cognitive workload is often used interchangeably with biological stress, although stress and mental workload are different constructs. Assessments of biological stress are concerned with measuring an individual's response to stimulus events that disturbs their equilibrium and taxes or exceeds their ability to cope. A wide range of physiological measures are used to measure biological stress, including average heart rate, heart rate variability, blink rate, and skin conductance. While not widespread in use, these types of metrics are used by human factors engineers and designers to measure surgeon performance when testing new ideas, concepts, and prototypes.
The Looking Glass — Reflected vs. True Motion
In traditional laparoscopic surgery, moving the robotic instrument in one direction causes the tip inside the body to move in the opposite direction. This is known as the fulcrum effect. For example, moving the surgeon's hand down brings the instrument tip up and vice versa. Everything is backward and presents a challenging learning curve for novice surgeons.
Experienced laparoscopic surgeons have learned to operate in reflected motion by making continuous real-time computations in their heads to flip what they are doing with their hands with what they are seeing. The broken mental model is that their movement input results in the opposite movement output. Regardless of how easy experienced laparoscopic surgeons deal with reflected motion, the fact remains that making these automatic adjustments in real time comes at a cost of the surgeon's cognitive bandwidth. All cognitive resources used to make these real-time compensations for working in reflected motion rob the surgeon of vital cognitive assets that could be used on the surgical procedure, rather than compensation for traditional laparoscopic instrumentation designs. It is difficult to see a case where reflected motion makes any sense.
The medical robotics industry is on fire. While only a few companies play in this space, all are significant global giants. Intuitive Surgical, the pioneer in the industry, remains dominant. Other companies including Johnson & Johnson, Google, Stryker, and Medtronic have all cut deals to move forward in some fashion into the robotic surgery space. And everyone is trying to figure out who is focusing on what surgical procedures to define how specialized their own robotic system needs to be and how to differentiate their platform from competitors.
It's hard to deny how robotics are transforming surgery. The naysayers who challenge the efficacy of going robotic versus traditional laparoscopic are muted. Robotics improve surgeon performance, minimize procedure invasiveness, and offer faster recovery times. As more competition enters this field, there will be a suppression in the cost of the systems as this industry morphs from a monopoly to an open market.
As technology evolves, augmented reality (AR) and virtual reality (VR) will play a more significant role in the human interface. The physical size and complexity of these robotic platforms will shrink, transforming them from current day monolithic pieces of hardware to smaller flexible designs that better adapt to the wide range of hospital architectures they are currently being shoehorned into today. The future of robotic surgery will not be singular, but also a convergence of nano-like surgical tools, on-skin and in-vivo micro wearables, and tissue/organ visualization technologies that will allow surgeons to see things they've never seen before. This industry is on the cutting edge of the next wave of surgical procedures and techniques.
In part 2, five critical success factors in the design of robotic surgical systems have been disclosed. Regardless of how sophisticated these robotic surgical systems are, their success boils down to designing human interfaces that allow surgeons to work in ways that are natural, intuitive, and unencumbered. These are fundamental human factors engineering issues that must be taken into account to develop high-fidelity robotic solutions that work the way humans think, feel, and behave.
This article was written by Dr. Bryce Rutter, founder and CEO of Metaphase Design Group Inc., St. Louis, MO. For more information, visit here.