Computer-assisted orthopedic surgery, robotics and navigation: What have we learned?

DiGioia and his colleagues use the HipNav navigation system to track the acetabular guide and pelvis during cup alignment and insertion. COURTESY OF ANTHONY M. DIGIOIA

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 OR, 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

Typical operating room set-up for modern virtual fluoroscopy system (iON-FluroNav, Medtronic/Smith&Nephew, Memphis, Tenn.) The camera is at the upper left and looks down onto the surgical field. A retrofitted calibration target is mounted on the conventional fluoroscopy unit. The workstation is visible in the background. COURTESY OF DAVID M. KAHLER

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.

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

The touch screen interface of the virtual fluoroscopy system. The surgeon can manipulate up to four radiographic images on the screen. The external fixator, reference frame with passive reflectors, and active drill guide are visible. COURTESY OF DAVID M. KAHLER

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.

MODERATOR Anthony M. DiGioia III, MD Renaissance Orthopaedics, PC Institute for Computer Assisted Orthopaedic Surgery, The Western Pennsylvania Hospital Pittsburgh, Pennsylvania William L. Bargar, MD Medical Director Sutter Joint Replacement Center Assistant Clinical Professor UC Davis School of Medicine David M. Kahler, MD Associate Professor Department of Orthopaedic Surgery Director of Trauma University of Virginia Charlottesville, Virginia Richard S. Laskin, MD Co-Chief of the Knee Service, Hospital for Special Surgery Professor of Clinical Orthopaedic Surgery, Weill Medical School of Cornell University New York, New York S. David Stulberg, MD Professor of Clinical Orthopedic Surgery Northwestern University Chicago, Illinois

In this round table on computer assisted orthopedic surgery, I have directed questions about CAOS technology to several experts. We will discuss the major considerations for adopting CAOS, such as cost and time; how CAOS can improve clinical outcomes; and the current status and future of these technologies in orthopedic practice.

Anthony M. DiGioia III, MD: Dr. Kahler, what does the clinician need to understand when he considers adopting CAOS into his practice?

David M. Kahler, MD: Those of us who were interested in this field in the early years felt that orthopedic trauma would probably have the most compelling applications for this new technology. Based on the exhibits at this year’s AAOS meeting, it seems clear that the implant companies are devoting most of their resources toward developing total joint applications. Nonetheless, image-guided surgery allows us to perform some pelvic trauma procedures with decreased invasiveness and more routine procedures such as intramedullary nailing with decreased radiation exposure. Despite the additional setup time required with CAOS, we have shown we can actually save OR time during iliosacral screw insertion.

Fluoroscopic navigation has now been commercially available for nearly four years. I am not sure why this technology has not yet been embraced by our traditionally techno-friendly specialty. I think that orthopedic clinicians in general are still quite wary of CAOS applications. There remains a widespread perception that CAOS systems are complicated and costly, and that they add little value to the practice of a capable surgeon.

The implant industry is very competitive, however, and will drive these systems to become less costly and easier to use in the near future. My gut feeling is that application-specific software, instruments and implants for CAOS will soon be readily available and that most orthopedic surgeons will be using them for some part of their surgical practice within the next decade. The advantages of this technology in terms of improved accuracy and decreased intraoperative radiation exposure are simply too great to ignore.

DiGioia: Dr. Bargar, what do you think clinicians should understand about CAOS applications?

William L. Bargar, MD: First of all, they should be aware that this is definitely coming. It is not a fad. CAOS will be required to meet the new goals of less invasive surgery with more rapid recovery. The patients will demand it.

Second, it will be take more time. Our challenge will be to minimize the extra time required, but there will be a required time investment both in the OR and in learning and preparation. Some additional preoperative or intraoperative imaging will be necessary for most systems. There must be an obvious return on that investment in time, both in better outcomes and lower complications.

DiGioia: Dr. Stulberg, do you agree?

S. David Stulberg, MD: Yes, CAOS is becoming available for a number of subspecialties in orthopedics, including spine surgery, trauma, sports medicine and joint reconstruction. Different forms of CAOS (image-based and image-free) may be appropriate for these different subspecialties.

At this time, I think that the practicing orthopedic surgeon should become aware of the general issues related to CAOS and should start to focus on those specific systems and applications that are most related to their practice. I believe that the first application a clinician should try is one that is related to an area of practice with which the surgeon is already quite familiar and comfortable.

Richard S. Laskin, MD: Accurate surgery is the goal in the operating room, and CAS is the facilitator that helps the surgeon reach that goal. It is a tool much akin to the image intensifier that we have used for more than 20 years of fracture care. During my orthopedic training, accurate placement of hip nails was a hit-and-miss procedure, and it was unhappily accepted that a certain percentage of fixed hip fractures would fail.

When I first began using the image intensifier to guide placement of the fixation devices 30 years ago, I was told that this was not necessary, was expensive, too costly, and just too difficult and high tech for the average orthopedic surgeon. Within five years it had become the standard. The same arguments are now being hurled when one discusses CAS for knee replacement, and now, as they were 30 years ago, will be proven wrong.

DiGioia: What clinical outcomes does it improve or show the most promise to improve?

Kahler: Good outcomes in trauma are almost always directly related to the avoidance of complications. In traditional ORIF of acetabular fractures, most of the reported complications result from surgical exposure of the fracture or inaccurate screw placement rather than from the original traumatic event.

We think that decreased output time and minimal invasiveness of CAOS, as well as improved accuracy in implant placement, will result in better outcomes due to avoidance of complications. It will take some time to demonstrate this conclusively.

Bargar: The most improvement will be in short-term outcomes. This represents a real shift in our thinking. We have always looked to long-term outcomes in orthopedic surgery, especially in the field of joint replacement. These short-term outcomes will be related to the coupling of CAOS techniques with less invasive surgery, such as less morbidity, shorter hospital stays and more rapid return to function.

The other area of outcome improvement will be in lowering the incidence of complications related to technical errors. This, of course, is an area of promise but is not yet proven. It is also possible that new complications may arise as a result of our dependence on this technology. It is incumbent upon the developers of these technologies to minimize the chances of CAOS-related complications. We must insure that our applications are as safe as possible. ‘First, do no harm.’

Laskin: I am obviously speaking as a knee arthroplasty surgeon answering this question. I feel that it will (and has already) helped us with more accurate alignment of the femoral and tibial components in the coronal and sagittal planes, as well has helping us more accurately place the femoral component in proper rotation.

Even more important, however, and more exciting for me, is the ability to use navigated instrumentation and trial components to aid in ligament balancing. Ligament balancing is difficult to teach because it requires so much subjective input for the surgeon. CAOS is now beginning to enable us to use objective measurable endpoints to determine ligament balance.

DiGioia: What are possible improvements in joint reconstruction, Dr. Stulberg?

Stulberg: In the area of joint reconstruction, CAOS has been consistently shown to make possible the alignment of implants and limbs that is as accurate or more accurate than the alignment achieved with mechanical instruments. More importantly, a number of studies (Jenny, et al.) have indicated that the number of outliers, ie, results outside of the accepted range of alignment, declines substantially when CAOS is used.

Moreover, the number of steps of each procedure that are accurate increases when CAOS is used. Some studies (Stulberg, et al, DiGioia, et al.) suggest that the use of mechanical instruments is improved when CAOS techniques are used. In addition, the use of CAOS in TKR results in a marked decrease in the need for ligament balancing procedures (Stulberg, submitted for presentation, AAOS, 2004).

DiGioia: What are the cost and time considerations?

Kahler: The systems that I have used for orthopedic trauma are costly — about $250,000. This doesn’t seem so extravagant when you realize that this is similar to the cost of a good, portable C-arm unit. I saw PC-based systems at AAOS this year that will cost less than $75,000 for the hardware.

After the initial hardware cost outlay that is absorbed by the hospital, most surgeons are concerned about adding operative time during setup of the computer guided surgery system. It takes only about 10 additional minutes at the start of the case to bring in a CAOS system. Attaching a reference frame to the appropriate portion of the patient’s anatomy adds another five minutes or so. The best systems have touch-screen interfaces that are entirely surgeon driven and eliminate the need for an assistant or technician.

We essentially always recoup the setup time by decreasing our reliance on intraoperative fluoroscopy and by gaining improved first-pass accuracy in implant placement. My residents have been quick to recognize these advantages in the past year and are starting to set up the system for routine fracture use, such as cannulated screw fixation of femoral neck fractures.

DiGioia: Dr. Bargar, what do you see as the increased cost?

Bargar: The increased costs will fall into three areas: imaging, OR time and equipment costs. If the imaging is done preoperatively, this cost should not have to be borne by the hospital since it will be done as an outpatient. If the imaging is done intraoperatively, this will represent another potentially uncompensated cost for the hospital. If it is done preoperatively, however, we will need to convince the third-party payers that it is worth it.

The cost of the equipment will most likely not be a capital equipment cost. Instead we should expect a charge by the CAOS company on a per-use basis. This will have to be worth the investment in terms of decreased length of stay. This may result in a real dilemma: Third party payers may pay the hospital less for these procedures specifically because there is a shorter length of stay. Hopefully, this can be compensated by the reduction in cost accompanying the shorter stay.

Stulberg: Image-free systems used to perform TKR currently cost between $100,000 to $150,000. It is anticipated that these costs will drop as usage increases and the cost of the computer hardware decreases. Moreover, as multiple applications become possible on a single unit, the cost per application will decrease.

The costs of these units can also be decreased if their used is related to a specific implant (eg, TKR). It takes approximately 10 cases to become reasonably comfortable with a typical image-free TKR system. During this period, the increase in time/case may be considerable (30 to 45 minutes). Initial cases should be scheduled with this in mind. Once the surgeon is familiar with a given image-free TKR application, the procedure using CAOS takes about 15 minutes longer than the procedure without it. This additional time results from the need to carry out the registration process. The time that it takes to actually perform the TKR using CAOS is not increased.

Systems vary substantially with regard to the complexity and length of time required to carry out the registration process. Surgeons should be aware of this when deciding which system to use.

The screen output of the virtual fluoroscopy system allows simultaneous viewing of four images to determine optimal trajectory for cannulated screw placement. The anterior column fracture line is best seen in the image at upper left (image 4). The virtual position of the drill guide is represented as a red line; the green line represents the predicted trajectory of the implant, the length of which is controlled by the surgeon. COURTESY OF DAVID M. KAHLER

Laskin: There are initial and ongoing costs. The initial costs related to purchase or leasing of the equipment are usually in the range of $100,000 to $250,000 for the surgical navigation console and screen purchase. Exact leasing costs depend on many factors including the system used and the length of the lease. Ongoing costs are usually minimal and cover the use of registration pins (which are now single-use items) and registration glions.

Using surgical navigation, since it adds several steps that are not used in a non-navigated system, adds some time to the procedure. For total knees there is the time required to insert the registration pins in the femur and tibia (about five to eight minutes), and localization of the hip and ankle joint through dynamic referencing (which takes about two to three minutes). Surface registration of surface landmarks can take from one to 10 minutes, and instrument registration another one to five minutes.

The extra time can be offset by its elimination of recutting that may occur when noncomputer navigated instruments are used. At the conclusion of the procedure, another one to two minutes are required to remove the pins and dress the pin sites. As the experience of the surgical team increases, these times will usually decrease; however, it will never take less time to perform a computer navigated TKR than it will a nonnavigated TKR.

DiGioia: Where does it fit into general orthopedic care currently and in the future?

Kahler: The most compelling early applications in orthopedic trauma involve pelvic and acetabular fractures. As the implant companies provide us with CAOS-specific instrument sets for more routine procedures, such as cannulated screw placement, I.M. nailing and osteotomies, CAS will find more widespread use in routine fracture care.

Bargar: Currently, the applications are limited. We have not yet successfully coupled CAS with MIS techniques. Navigation systems are only now coming on the market. These are first-generation systems that will need much refinement to smoothly integrate into current care models. Some pioneers and interested techies are already using them, but this is a small percentage of practicing surgeons, and represents an even smaller percentage of the total number of orthopedic procedures done today.

In the future, by coupling with MIS and by refining and streamlining the systems and how they interface with the surgeon, I believe CAS will become a necessary and integral part of the best surgical techniques.

Laskin: Our accuracy in making the bone cuts in a total knee replacement for a patient with a nondeformed knee is normally very good. The accuracy of the resections, especially in the sagittal plane, decreases on the tibial side especially in obese patients. Likewise, in a study we presented at the AAOS in 2003, we found that our accuracy in patients with severe valgus knees (that is with anatomical axes greater than 15º) diminished greatly using standard intra- and extramedullary femoral referencing instrumentation.

These types of deformities and knees in obese patients are areas that, I feel, will be good indication for using some type of surgical navigation.

Stulberg: I believe that CAOS is a useful tool for the orthopedic surgeon who does a reasonable number (30 to 50/year) of a given procedure and wishes to improve his/her skills in this area.

DiGioia: What will these enabling tools allow us to do now and in the future?

Kahler: Currently available image-guided surgery (IGS) technology allows unparalleled accuracy in implant placement. Once a fracture is reduced, it is no longer difficult to place a cannulated screw exactly where we want it. This is especially useful around the irregular anatomy of the pelvis, where we now have sufficient accuracy to place screws within 5 mm of the intended target in nearly all trajectories.

There has recently been increased concern about intraoperative radiation exposure to both patient and surgeon during C-arm fluoroscopy. Measurable adverse health effects can result from the amounts of radiation that we and our patients absorb during fluoroscopic procedures. IGS technology greatly reduces intraoperative radiation exposure by decreasing the number of individual images required during implant placement.

The holy grail of IGS for fracture care has always been virtual fracture reduction, or the ability to track individual fracture fragments during reduction maneuvers without using real time fluoroscopy. Instrumented reduction rods that are tracked by the computer currently allow virtual fracture reduction for long bone fractures.

I have also seen fracture reduction software packages that will allow virtual reduction of fractures by marking docking points and matching them up during manipulation of the fragments. These will hopefully be validated soon for clinical use.

The surgeon must still guide the tool and perform the surgery. COURTESY OF ANTHONY M. DIGIOIA

Bargar: At this time, most of these tools are navigation guides that act like GPS systems for the body. They can provide us information about where a tool is in space relative to a particular bone. The surgeon must still guide the tool and perform the surgery. Although this is attractive because it maintains the traditional role of the surgeon, it still allows for human error. It also means that the surgeon must deal with new information that requires multiple choices and decisions not before encountered. This can slow the surgery and creates a significant learning curve.

Active robots, however, provide the opportunity to eliminate human error and execute the surgical plan in a precise and reproducible manner. ROBODOC, the first (and currently only) active surgical robot is completing its second multicenter study and should be on the market next year.

In the future, you will see the combining of navigation and active robotics. Parts of some procedures lend themselves more to navigation to provide tool tracking for the surgeon (eg, acetabular cup placement), whereas other parts require more precision execution that is offered by active robots (eg, femoral stem preparation). By combining these tools the surgeon can most efficiently take advantage of what they have to offer.

Stulberg: Currently available CAS tools in selected areas (eg, TKR) allow surgeons to reduce the variation in alignment of each step of the procedure and allow surgeons to actually measure the precision with which each step of the procedure is performed. In the not too distant future, CAS will facilitate the performance of various MIS procedures. They also lead to improvements in instrument and implant design. Current tools reduce the need for often difficult to perform soft tissue balancing procedures.

DiGioia: What will be the impact of CAOS tools in MIS techniques?

Laskin: Surgical navigation and minimally invasive knee replacement are a natural partnership. Navigation will allow “visualization” of landmarks that might otherwise be difficult to discern through a smaller incision. We have found that a modification of the technique is needed, however, in which the femoral pins are inserted percutaneously since our incision rarely extends further proximal than 1 cm to 2 cm from the patella.

Kahler: MIS has been the catch phrase for trauma for over a decade. If the surgeon can indirectly reduce a fracture and then obtain good images in multiple planes, many pelvic, acetabular, and long bone fractures may be treated using IGS with minimally invasive technique. In all cases, the surgeon must have the diligence to obtain good images and the discipline to abandon the MIS procedure and convert to conventional open technique if necessary. Surgeons in the next generation will need to be trained in both conventional and minimally invasive IGS techniques.

Bargar: MIS is an application of CAS that will demonstrate that these new tools are truly enabling. MIS by definition is surgery with less exposure. We were all taught in training, however, that the three most important things in surgical technique are exposure, exposure, exposure. By eliminating many visual cues, MIS demands that we find other ways to ensure exact surgical technique. CAS tools will provide needed information to the surgeon, shorten the learning curve and avoid errors in technique. Not only will current MIS techniques become better and more accurate, but with these enabling tools new techniques will evolve and allow surgical procedures not yet imagined.

Stulberg: In situations in which imaging is required to carry out a MIS technique (eg, pelvic trauma, two-incision THR), CAOS will reduce the amount of time this imaging modality needs to be used (eg, fluoroscopy). CAOS may also make possible the use of smaller incisions by allowing relevant anatomy to be seen with CAOS techniques. Soft tissue trauma, an important consequence of MIS, will be reduced by CAOS as a result of the precision with which exposure of relevant anatomy can take place and as a result of the increased accuracy of implant position that reduces the need for additional soft tissue trauma, eg, soft tissue balancing in TKA.

DiGioia: How should a surgeon learn a CAOS technique?

Stulberg: He should become proficient in a given area of orthopedic surgery using currently available instruments, visit and observe a surgeon who uses the CAOS technique that he is interested in trying, use CAOS as a measurement tool with the mechanical instruments that he currently uses, and use the specialized CAOS tools to do the specific procedure.