Surgery comes from the Greek word cheirourgia, which means “performed by the hands” and it is a healing practice that goes back thousands of years. The literature offers insights on early surgical techniques performed in different historical periods of human development, which reveals that the physical manipulation of human body structure was on the agenda of many ancient civilizations.
Nevertheless, the lack of effective antiseptics, anesthesia, and medical accuracy was a severe limitation to the scope of surgery, which was considered as a last resort for patients and practitioners. Due to the painful and brutal nature of the procedure, added to the high chance of not surviving in the operation table, some patients chose to die from their medical conditions or commit suicide than undergo the surgeon’s knife. Surgical procedures evolved over the centuries with respect to instruments, pain control, infection prevention and, most importantly, surgical techniques, resulting in enhanced medical treatment and ultimately extending human lifespan.
Fast forwarding to the late twentieth century, minimally invasive surgery (MIS), a.k.a. Laparoscopy is a modern surgical technique that allowed interventionists to perform operations through small incisions (usually 5 – 15 mm) using laparoscopic instruments. There are a number of advantages of laparoscopic surgery versus open procedure for the patients including reduced hemorrhaging and pain, minimized exposure of internal organs to contaminations and ultimately short postoperative stay in the hospital.
Whereas laparoscopy is visibly advantageous in terms of patient outcomes, there are still some obstacles from the surgical practice perspective that prevent this procedure from being the surgeons’ first choice for some surgical interventions. Firstly, advanced laparoscopy is more difficult to learn, perform and master when compared to traditional operations. Other inherits drawbacks are (a) limited motion (degrees of freedom) due to straight laparoscopic instruments and fixation enforced by the small incision in the abdominal wall; (b) impaired vision, due the two-dimensional imaging impeding deepness perception and unstable video camera manipulated by inexperienced camera-holders; (c) usage of long instruments amplifies the effects of surgeon’s tremor, hindering suture and tissue grasping; (d) poor ergonomics imposed to the already mentally and physically stressed surgeon; and (e) loss of haptic feedback, which is distorted by friction between the end-effector instrument and trocar, reactionary forces from the abdominal wall and friction on the grasping mechanism.
The Minimally Invasive Robotic Surgery (MIRS) offers solutions to either minimize or eliminate many of the pitfalls associated with traditional laparoscopic surgery. Current available MIRS platforms, such as, for example, the Da Vinci Surgical System approved by the U.S. Food and Drug Administration in 2000 was clearly a historic mark on the surgical treatment. The ability to leverage laparoscopic surgery advantages whereas augmenting surgeons’ dexterity and visualization and eliminating the ergonomic discomfort of long-lasting surgeries, makes MIRS undoubtedly an essential technology for the patient, surgeons and hospitals.
However, despite all improvements brought by currently commercially available MIRS, haptic feedback is still a major limitation reported by robot-assisted surgeons once all-natural haptic feedback is eliminated because the interventionist no longer manipulates the instrument directly. Haptics is a conjunction of both kinesthetic (form and shape of muscles, tissues and joints) as well as tactile (cutaneous texture and fine detail) perception and is a combination of many physical variables such as force, distributed pressure, temperature and vibration. Direct benefits of sensing interaction forces at the surgical end-effector are (a) improved organic tissue characterization and manipulation, (b) assessment of anatomical structures, (c) reduction of sutures breakage and (d) overall increase on the feeling of assisted robotics surgery. Considering that learning curve and surgical dexterity are two parameters that are used to compare surgical methods, haptic feedback also plays a fundamental role in shortening the learning curve for young surgeons in laparoscopy surgery training. That said, performing surgery without such sensory information could lead to increase of vital organic tissue damage and limit the widespread adoption of MIRS.
Added to the inherent complexity of measuring haptics, being the latter a multi-variable physical quantity, engineers and neuroscientists also face important issues that require consideration during sensor design and manufacturing stages. The placement of the sensing element, which significantly influences the quality of the force measurement, leads sensors designers to a dilemma: either placing the sensor outside the abdomen wall near the actuation mechanism driving the end-effector (a.k.a. Indirect Force Sensing), or inside the patient at the instrument tip, embedded on the end-effector (a.k.a. Direct Force Sensing). The pros and cons of these two approaches are associated with (a) measurement accuracy, (b) size restrictions and (c) sterilization and biocompatibility requirements. Table 1 compares these two force measurement methods.
Table 1: Comparison between Direct vs. Indirect Force Measurement.
Tissue contact forces are masked by friction between the instrument trocar and the insertion port. Measurement distortion is also caused by mechanical linkages connecting the end-effector and the actuator (strings) and gravitational effects of mass along the instrument axis.
This method does not consider gripping forces at the end-effector.
Frictions and transmission disturbance forces does not affect the haptics feedback measurement once the sensor is located near the end-effector.
This approach allows the measurement of gripping forces at the jaw of the end-effector.
The sensing element needs not to pass thru the insertion port (abdominal wall), meaning there are not many dimensional and material constraints.
Abdominal laparoscopic insertion ports range from 5 to 15 mm, which severely limits the sensor to only ~12 mm in diameter.
Sterilization and Biocompatibility
Components that lie outside the abdominal cavity need not be sterilized to complete destruction of microorganisms before its utilization.
Must follow standard sterilization used for surgical instruments. Sterilization protocol in an autoclave determines 121 °C and 205 kPa steam for 4 to 15 minutes.
Bonding agents, microelectronic components, strain gages, and electrical conductors must be able to withstand these temperatures and pressures.
In the MIRS applications where very delicate instrument-tissue interaction forces need to be precisely feedback to the surgeon, measurement accuracy is sine qua non, which makes direct sensing the ideal option. An indirect benefit of accurate real-time direct force measurement is that data collected from these sensors can be utilized to produce accurate tissue and organs models for surgical simulators used in MIS training.
However, this novel approach not only brings the design and manufacturing challenges depicted in Table 1 but also demands higher reusability. Commercially available MIRS systems that are modular in design allow the laparoscopic instrument to be reutilized approximately 12 to 20 times. Adding the sensing element near to the end-effector invariably increases the cost of the instrument and demands further consideration on the design stage in order to enhance sensor reusability. Appropriate electronic components, bonding material, gages and conductors are needed to withstand additional autoclavable cycles. Special design requirements might increase the unitary cost per sensor, however extended lifespan consequently reduce the cost per cycle and brings commercial affordability to direct measurement method.
The surgical robotics industry undergoes a significant momentum in which fresh capital is not only coming from venture capitalists or private equity funds but also giants of medical industry and technology firms are making a bet in the increase in need for automation in the healthcare sector. An extensive list of surgical robotic companies is pursuing a marketable product including haptic feedback whereas few specialized sensor technology companies combine the competences to offer a measurement solution that meets all design requirements imposed by direct force measurement in MIRS: miniaturization, biocompatibility, autoclavability, high reusability and measurement accuracy.
The Greek word cheirourgia still holds true in the modern surgery practice and the hands of a well-trained interventionist can still not be substituted for a surgical robotics platform. Nevertheless, the evolution of MIRS and the addition of new technologies such as haptic feedback and direct force measurement, undoubtedly benefits the surgical practice, patients and unveils new frontiers in medicine.