More and more partial knee replacements are being performed with the aid of navigation systems, which come in an ever-increasing array of options. There’s computer-assisted navigation, robotic-assisted surgical technology and systems that convert scans into custom 3D cutting guides. “Image-guided can mean so many things today,” says Ronald Anthony Navarro, MD, the regional coordinating chief of orthopedic surgery at the Southern California Permanente Medical Group in Pasadena. “They all promise to make the surgeon’s technical job easier and to let us become better surgeons.”
These advances that digitize the patient’s anatomy share one thing in common. They give the surgeon greater accuracy and precision in placing the implant and aligning the leg on the mechanical axis than ever before, certainly better than relying on vision and intuition.
“Software-guided knee surgery has the potential to not only streamline the surgical process, but also to improve the mechanical alignment of the knee and thereby optimize patient outcomes,” says orthopedic surgeon John A. Peters, MD, of Kaiser Permanente South Bay Medical Center in Harbor City, Calif., who specializes in adult reconstruction of the hip and knee. Here’s a review of some of what’s available.
- Computer-assisted navigation. With fluoroscopy-based navigation systems, you tap metal markers into the knee to serve as bony anatomical landmarks, explains Dr. Navarro. A small series of fluoroscopic images capture these markers. A software program synthesizes these images to relate the surgical area in space, and identify the position of the instruments and implants. A step up from this is 3D fluoroscopy-based navigation, which lets you visualize the surgical area in the axial plane as if you had an intraoperative CT scanner. Imageless (radiation-free) navigation systems construct a model that fits the registered surface points from its many stored CT scans.
“The computer can map the coordinates of this bone in my system so I see what the true axis of the bone is with respect to the ends of the tibia and femur,” says Dr. Navarro. “I can do surgery in a way that is enhanced. I get a better understanding of the angles and directionality when I’m making my guided cuts.”
Few question whether computer navigation improves axial limb alignment and implant positioning in total knee arthroplasty (TKA) over conventional surgery. And there’s anecdotal evidence that it leads to more efficient and faster surgery. Yet orthopods are still waiting for the evidence that clinical outcomes are appreciably better when you reduce TKA alignment outliers. Most navigation system studies show improved accuracy and better post-operative imaging, but the proof that patients are experiencing less pain and better functionality is lagging. “Does this make a difference in the patient’s outcome? That’s still being debated, but I think you can assume that if you align the knee more consistently, outcomes probably will follow that,” says Dr. Peters.
- Robotics. The surgeon uses patient-specific 3D computer mapping and an interactive, handheld robotic arm system to resurface the diseased portion of the knee joint and replace it with an artificial implant. The robot technology guides the surgeon to precisely prepare the bone surface and accurately place and align the implant. Patient benefits of using robotic technology for partial knee replacement can include less bone removal, improved surgical accuracy and optimal implant positioning.
“It’s a technology I think you’ll see more and more of, since unicompartmental knee replacements are now being done frequently in surgery centers,” says David Geier, MD, a sports medicine specialist and orthopedic surgeon based in Charleston, S.C.
- Custom cutting guides. The end result here is a 3D printout of a custom jig — a plastic cutting guide — that directs the surgeon’s incisions. After you make the incision, you put the prefabricated, customized cutting block on the ends of the femur and tibia to help the surgeon position the knee components. All planning and sizing takes place pre-operatively with technology that produces patient-specific instruments. The printout is made based on an extremity MRI or CAT scan. “This is a real time saver in surgery,” says Dr. Peters, who has used custom jigs in about 15 cases. “It also takes some of the uncertainty out of your cuts because you’ve used a computer to align the leg and design your cuts exactly how you want them instead of relying on some standard angle cuts.”
A report in the September 2013 Journal of the American Academy of Orthopaedic Surgeons observes that “the use of patient-specific instruments for total knee arthroplasty shifts computer navigation for bone landmark registration and implant positioning from the intraoperative to the pre-operative setting.”
Another key benefit of the custom cutting jigs, says Dr. Peters, is that there’s less risk of fat embolism and less blood loss because you don’t have to insert metal rods inside the bones to guide the incisions. This could also shave 10 minutes off the procedure time. Plus, because you don’t need any instruments for alignment, you need fewer instruments at surgery. “You have fewer instruments to turn over and sterilize, which makes for a faster setup and faster surgery,” says Dr. Peters.
One study reported that overall surgical time was 6.7 minutes shorter with patient-specific instruments compared with conventional instruments. “If you’re doing 6 [arthroplasties] a day, you can probably do 7 cases a day using these cutting blocks,” says Dr. Peters.
For all of surgical navigation’s gee-whiz appeal and the traction it is gaining, the vital question remains unanswered: Does it improve clinical patient outcomes or reduce complications? On that, the jury is still out.