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Computer-assisted orthopaedic surgery, robotics and navigation: What have we learned?
--- Anthony M. DiGioia III, is director of the
Institute for Computer Assisted Orthopaedic Surgery at the Western Pennsylvania
Hospital in Pittsburgh, U.S.A, and is one of the co-founders of
CAOS-International.
Computer-assisted orthopedic surgery is at a crossroads. There have been many initiatives that have now brought these technologies from the drawing board all the way to clinical use and now commercial development. At many sites, computer assisted surgery tools are being used on a routine basis, but there are continued challenges in the clinical adoption and routine use of these surgical tools.
Computer-assisted orthopedic surgery [CAOS]-based technologies are the surgical toolbox of the future and represent a spectrum of devices including 3-D image-guided and nonimage-based navigation systems, intraoperative fluoroscopic navigation, robotic-assistive tools, and new intraoperative visualization devices. CAOS tools couple simulations with real time evaluations of surgical performance.
Currently, we have a limited ability to couple preoperative planning with surgical implementation or to integrate medical imaging directly into the operating room. We lack tools, sensors or measurement devices that provide timely and accurate intraoperative data like the position of bone, tool and cutting-guide orientation or location of implants.
The new paradigm of CAOS will couple and tightly integrate planning and imaging with the surgical intervention, permit simulation and optimization of a patient-specific preoperative plan and integration of medical images directly into the operating room, provide a new generation of measurement devices and sensors providing intraoperative information to surgeons, and become a great educational and training tool.
Possibilities, limitations
CAOS tools and technologies can assist and complement; they do not replace surgeons. With computer assisted devices and tools, surgeons can accomplish surgical tasks neither could do alone. With the recent interest in less and minimally invasive joint replacement and the rediscovery of partial joint resurfacing as well as future potential for biologic implants, CAOS-based tools have the potential to impact daily clinical practice the same way that fiberoptic technology has revolutionized the way we currently practice in many orthopedic subspecialties.
Balancing these new capabilities are the potential negative aspects of introducing new technologies into clinical practice: the real costs and time costs for preoperative or intraoperative imaging that may not normally be used in routine practice, costs of the systems themselves, increased operating time, accuracy and validation, and surgeon acceptance.
CAOS technologies have the potential to be used in different capacities: research tools, training tools, in routine clinical practice, as a commercial proposition, and as an enabler for less and minimally invasive surgical techniques. CAOS technologies will likely be important in all of these roles. However, the most powerful argument for their use may be that they enable surgeons to develop techniques that are more accurate, less and minimally invasive.
Classifications and definitions
CAOS tools range from an active robotic system capable of performing surgery autonomously to passive or navigation systems that provide additional information during a procedure but do not perform the surgical action. The surgeon controls the intervention but acts on information.
Navigation is analogous to a surgical information system. The spectrum of tools represent the classification system based on control and safety. The FDA reviews the approval process for the passive- or navigation-type systems, for the most part, as a 510(k) process because the surgeon is the end effecter and controls the surgical tools. This is in contrast to the active or robotic tools, which require obtaining an investigational device exemption. These tools work under their own software and hardware control for at least a portion of the procedure.
Over the last several years a spectrum of surgical navigation systems have been available. These range from ones that use preoperative images, such as CT scans, to systems that use intraoperative imaging with fluoroscopy, to systems that do not require any images preoperatively or intraoperatively, for these “image-free” navigation systems use information that is collected during surgery — such as centers of rotation of the hip, knee and ankle and visual information like anatomical landmarks.
Each of these approaches has certain limitations and benefits. Clinical functionality is most important. For instance, CT-based systems provide complete and full functionality. Fluoroscopic navigation systems are amenable to any application that already uses fluoroscopy to reduce the radiation exposure time. However, navigation is on the image that is obtained rather than on the patient’s true anatomy. Any limitations in the fluoroscopic images would also carry over into the limitation of the navigation system. In addition, although imageless type navigation systems provide the opportunity to do away with any images, the information collected will determine the functionality in the system and may not have the complete functionality of a CT or image-based system.
Steps to navigation
There are three steps necessary to navigate. The first phase is data acquisition preoperatively or during surgery, including preoperative images, fluoroscopic images, or kinematic information such as the determination of center of rotation or anatomic landmarks during surgery.
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The next two steps — tracking and registration — are necessary to take that information and use it during surgery. Registration may be a foreign term to surgeons, but we routinely do this process with any of our surgical interventions. Registration is the ability to relate images such as x-rays, CTs or MRIs and a patient’s 3-D anatomy to the anatomical position on the surgical field. Registration is the way to teach the navigation systems the same process.
Several techniques have been developed for this registration process. The early techniques required the use of pins or fiducials for robotic-type devices. However, these pins were placed in a second surgical procedure that needed to be done prior to the scanning and were applied in places that were not in the primary surgical field. Due to these drawbacks, pinless type registration was developed in which the unique shape of the bone was used to achieve the same goal and did not require pins or separate incisions or procedures.
This surface-based registration has become the gold standard for CT-based navigation because of its high level of accuracy and reliability. Using this technique for registration, a cloud of surface points on the bone is collected using a tracked probe. The unique shape of the bone is then used to match the preoperative plan with the position of the patient in the operating room.
In fluoroscopic navigation, the registration process is in essence automatic and is performed on-line as long as the bone and fluoroscope are tracked when the images are obtained. Registration in imageless systems is a matter of collecting the centers of rotation of joints through kinematic testing or by having the surgeon visually collect important landmark points.
Tracking becomes important because we need sensors and measurement devices that can provide feedback during surgery on the orientation and relative position of tools to bony anatomy so that we can act on that information in a timely manner. By attaching optical or electromagnetic trackers to regular surgical tools, we can convert our current tools to smart tools in which we can know the position and orientation of the tools’ alignment with respect to the bony anatomy of interest, all in real time.
Intraoperative measurement tool
Once you achieve tracking with registration during surgery, you have a real-time intraoperative measurement tool that can provide timely information to surgeons on the relative position of tools to the bony anatomy. As a secondary benefit, you have the power of the imaging modality on-line during the surgery and can access those images during the actual procedure.
One way to become comfortable with using a navigation system clinically is to first use the system as an intraoperative measurement tool. In other words, the system can be used by the surgeon just to measure what you currently do. Measure the accepted technique or guides that you currently do and use the navigation system to document your current technique. After you obtain confidence in the use of the system and the information that it provides, you then can use the system to actually navigate parts of your procedure. It is always important to validate the CAOS technique both intraoperatively and clinically, remembering that the most important factors are improving patient outcome.
There is a spectrum of navigation technologies. The clinical functionality you want out of a system determines what type of CAOS system should be best applied. We have all learned in the past that one tool cannot solve all our clinical problems. Probably, the CAOS platform of the future will include a spectrum of these tools all in one platform. What is necessary? Only the surgeon knows for sure.
So what are the costs? Costs include surgeon time both before and during the actual procedure, additional operating room time, additional technician time, and the actual cost of the hardware and software for the navigation system itself. In the end, however, the most important factors in the adoption of the CAOS technologies will be ease of use for surgeons and OR staff, and documented improved patient outcomes by obtaining more accurate and reliable alignment and less invasive techniques.