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CAS adds precision to several types of orthopedic surgery
Computer-assisted navigation technology takes the guesswork out of some orthopedic operations.
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While experience and practice help considerably, they can never entirely remove the imprecision from human hands and eyes. Some orthopedic surgeons have begun to turn to computer-assisted surgery instruments to eliminate some of that inaccuracy and guesswork.
“There have been [several studies] that have looked at experienced orthopedic surgeons, and they get the [acetabular] cup in right most of the time, but not all the time. Researchers ask, ‘Why does someone who has done 2000 of these still not get it right?’ It’s because patients are rolling back and forth,” said Richard Laskin, MD, of the Hospital for Special Surgery in New York. Laskin performs many total knee replacements as well as total hips, and he uses computer-assisted navigation to remove those possible errors from his operations.
Computer-assisted surgery (CAS) systems provide a map of the operative area, be it the femoral or acetabular side of a total hip replacement (THR), the knee joint, the spine or various sites for trauma applications. Some systems use CT scans to create the image needed for the computer to assist, while others rely on handheld probes to preoperatively map out the bone. Laskin said he prefers the imageless systems to those that use CT scans or fluoroscopy.
“For spine surgeons, a CT scan is fine since a CT is usually a part of the preop work-up of the patient,” Laskin told Orthopedics Today. “But for a total knee surgeon, to have to now get a CT scan on a patient becomes very difficult. It is time consuming, and no one has yet answered who’s going to pay for it.”
Likewise, “Trauma surgeons often routinely have a fluoroscopy unit in the OR, so they are comfortable with a fluoroscopy-based CAS system. For most total knee and hip replacements, however, I think that an image-free system is accurate and is more preferable,” he said.
Advantages of CAS
CAS provides several advantages over traditional instruments in joint replacement surgery, Laskin noted. With standard instrumentation, the accuracy of the bony cuts generally falls around ±2º; CAS cuts can improve this number to 0.5º or 1º.
Laskin said that this improvement in accuracy, while significant, has not yet been shown to improve the longevity of the arthroplasty, but ongoing studies are looking into this. A more important advantage may be the ability to better balance the soft tissues in knee replacement.
“Soft tissue balancing is always the hardest part to teach a new surgeon because there are no real instruments to balance the soft tissues. That’s a big advantage of CAS. One can tell whether one side is too loose and gapping or if it is too tight,” Laskin said. “It helps surgeons titrate and look at soft tissue balance in a way that we could not do in the past.”
CAS also eliminates the need to insert instruments in the intermedullary canal, according to Laskin.
“If you put alignment rods in the intermedullary canals, there is a small but real chance of developing fat embolism syndrome. This risk is markedly diminished using CAS,” he said.
Obstacles and challenges
More surgeons are using navigation technologies in the orthopedic OR, but there are still obstacles to complete integration. The systems are still costly, somewhat cumbersome to use, especially in a laminar flow enclosure, and more importantly, they add time to the operation. Laskin said that at present, surgeons can expect to spend from 10 to 30 minutes longer on a CAS operation than on a traditional surgery.
“As we continue to work on making the navigation screens more intuitive and the tracking instruments easier to use, surgeon adoption will increase,” he said.
“I think they’ll become routine only if we can make it so that the average orthopedic surgeon can do a CAS procedure and not add a significant amount of operative and anesthesia time to the surgery,” he said. “Surgeons may not use computer navigation for every case, but they may find it beneficial in patients with deformed limbs or in those who had prior surgery.”
Laskin is also studying their use in combination with a minimally invasive technique that he refined and reported on at the recent American Academy of Orthopaedic Surgeons (AAOS) meeting in Washington.
Michael Fracchia, MD, president of Long Island Bone and Joint in New York, said that the computer systems add 10 minutes, but performing minimally invasive operations with this technology can add another 10 minutes as well.
“I think the advantages to the computer are, without question, worth [the extra time]. I think there’s increased accuracy, I think there is faster rehab with the computer, and the computer allows us to do things through a smaller incision,” Fracchia said. “I’m not sure that we should be doing MIS on every patient, but I have no problem using the computer on every patient.”
In recent years, companies have improved the usability of the screens, instruments and programs, all of which reduce operating time, he said.
“Will it ever take less time than a regular operation? No. I’m aiming for the same or maybe five or 10 minutes more at max,” Laskin said. “We’re pretty close to that, and not for me, because I’ve done lots of them, but for the guy who’s doing 35 or 40 knees a year. If we get to that point, I think there is no question [CAS] will become part of the OR.”
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The ability to verify
S. David Stulberg, MD, a professor of orthopedic surgery at Northwestern University Feinberg School of Medicine, said that the extra time comes largely from the new ability to check and recheck the accuracy of cuts.
“The time is not so much in the actual issues related to using the computer, such as putting on the pins and doing the registration. Where you add time is in the constant checking that’s available to you,” he told Orthopedics Today.
“When you have the option of seeing how you did and seeing if it all fits, it does take longer because you’re thinking about it more and because you’re checking more. But I have a little trouble thinking that’s a bad thing.”
Another possible barrier to spreading the use of CAS lies in the lack of adequate support from the companies who make the equipment and software, Stulberg said.
“Orthopedic companies, with the exception of a couple, are really not equipped to instruct or support surgeons in the use of this technology. When you do a total knee these days, you have a tech in the room who knows the instruments, he knows the implants, he can extensively assist you in the procedure. That support is, by and large, not available [for CAS],” he said.
“What happens is that these units get dropped off at surgeons' ORs, and the surgeon may have a support staff there for one or two cases, and that’s basically it. That is a significant barrier to allowing a surgeon to get comfortable with this [technology]. So, until the industry gets on top of that as a whole, it’s going to be difficult,” Stulberg said.
Trauma applications
While the added time may present a problem in joint replacement applications of CAS, trauma surgeons can perform certain operations either at the same rate or faster than without the navigation. David Kahler, MD, of the University of Virginia, uses CAS for percutaneous treatment of pelvic and acetabular fractures.
“We’ve thought for a long time that trauma really has the most appealing applications in all of the orthopedic fields in terms of the applicability of CAS, just because we can decrease the invasiveness and improve the accuracy with the placement of implants, and also decrease radiation exposure pretty dramatically, to both patient and surgeon. Up until recently all we had was the ability to show a trajectory of a drill guide superimposed on stored images of a fractured bone. And although that’s very useful it doesn’t do the things that we need to be able to do better in the OR, and those are reducing fractures and placing implants other than guidewires and screws,” Kahler told Orthopedics Today.
Several companies have recently begun to focus on trauma applications, however, and Kahler thinks these uses will pick up steam. The development of application-specific software packages will allow surgeons to use a program specifically for a certain operation, such as femoral nailing. He pointed out that studies have shown that as much as 30% of repaired femoral fractures are malrotated, and CAS can largely eliminate this problem.
During fluoroscopic navigation, several fluoroscopic images are taken before beginning the operation, and the software uses these images to guide the surgeon through the operation step by step. Perhaps the biggest change is in the dramatically reduced radiation exposure. “You have the potential to do the whole thing with as few as six individual fluoroscopy shots, as compared to the usual three or four minutes of C-arm time for femoral nailing.” Kahler presented a study at the AAOS annual meeting that found equivalent operative times and more than a 50% reduction in radiation exposure using CAS for insertion of a single screw across the SI joint.
Looking ahead
While CAS has yet to catch on among some surgeons, an even smaller group has made an even bigger leap to using robotics for certain operations. William Bargar, MD, of Joint Surgeons of Sacramento, Calif., has been involved in the development and use of robotic orthopedic surgery systems since the mid-1980s. This and other robotic systems combine the concepts of navigation with computerized arms and instruments that perform the delicate parts of surgery without the aid of human hands.
“There’s no question that robotics will play a role in almost all surgeries further down the road,” Bargar said. “There are certain things at which a machine is better than a human. I actually think, compared to modern engineering and manufacturing techniques, we’re relatively antiquated.”
In order for robotics to move forward, however, costs must come down and surgeons must be prepared to relinquish a sense of their hands-on control in the OR — something many surgeons are unwilling to do.
For now, surgeons and companies are focusing on navigation systems and expanding their indications.
“I think navigation is here to stay; I don’t think it’s a phase,” Fracchia told Orthopedics Today. “I think people are intimidated by it, but I don’t think they should be. With the right software, it’s a relatively quick learning curve.”
As the systems continue to improve and surgeons learn to use them more effectively, the orthopedic OR of the future doesn’t seem so far off.
Dr. Kahler is a paid consultant to BrainLab.
For more information:
- Berger RA, Bonutti PM, Laskin RS, et al. Less and minimally invasive joint replacement: fact and fiction. Instructional course #201.
- Kahler DM, Polstra K. Computer-assisted fixation of posterior pelvic ring disruption compared to standard fluoroscopic technique. #221. Both presented at the American Academy of Orthopaedic Surgeons 72nd Annual Meeting. Feb. 23-27, 2005. Washington.