Sculpting a better fit for knee and hip implants
Orthopedic surgeons are doctors, but they are also artisans, sculpting bone so that it fits snugly with artificial hips and knees.
But even the best artists make mistakes, says Dr. William Bargar, an orthopedic surgeon at Sutter General Hospital in Sacramento, and the imperfections that are charming in handicrafts have no place in modern medicine. That’s why he invented the bone-drilling Robodoc.
The robot, which excavates bones to make room for knee and hip replacements, is made by Curexo Technology Corp. in Fremont, Calif. It and the Robotic Arm Interactive Orthopedic System (called RIO) made by Mako Surgical Corp. of Fort Lauderdale, Fla., are designed to minimize human error and turn surgical art into operating-room engineering.
“When I use a robot and I walk out of the operating room, I know it’s right,” says Dr. Larry Dorr, an orthopedic surgeon at Good Samaritan Hospital in Los Angeles who helped develop a new hip socket-shaping tool for RIO.
For a hip or knee replacement to be comfortable and useful, the implant must fit precisely into the bone. But standard methods for shaping or excavating bone are downright crude, Bargar says. During hip surgery, for example, surgeons hammer down on a small-to-large series of cutting tools called broaches. “You just slam [them] right in,” Bargar says.
That force can cause fractures. And if a surgeon makes a hole at the top of a leg bone that’s not a perfect fit for the hip implant, it may cause pain or make the person’s leg longer.
It’s not a rare event: Bargar estimates that poor fit in the leg bone happens in 10% to 20% of hip replacement surgeries. On the other end of the implant, fully half of all patients wind up with a device that doesn’t fit perfectly with the hip socket, according to a February study in the journal Clinical Orthopaedics and Related Research.
Precision cut
Robots, Bargar says, can help eliminate those ill-fitting implants and give more people good results with their new joints.
RIO is a $1.3-million robotic arm that helps the doctor drill precisely the right cavity. Surgeons have been using the device to perform more than 8,000 partial knee replacements at 86 locations across the country since 2006, and the company began offering a hip-socket attachment in September.
The surgeon uses a CT scan to decide ahead of time where the implant will go, then uploads that plan to the boxy, one-armed robot. In the operating room, when it comes time to shape the bone, the surgeon guides the robot’s drill by hand -- but when it gets close to the edge of the planned cavity, the robot offers resistance and won’t let the doctor cut beyond the planned space.
Without the robot, a partial knee replacement -- which preserves more of the joint’s motion -- is difficult, says Dr. Maurice Ferre, Mako’s chief executive. Even if partial replacement is an option, many surgeons prefer to replace the entire knee, he says. Partial replacements account for 8% of knee replacements, according to a 2008 paper in the Journal of Arthroplasty.
The implant for a knee replacement should be placed at a right angle atop the shin bone, says Dr. Jess Lonner, an orthopedic surgeon at the Rothman Institute in Philadelphia who is a Mako lecturer and shareholder. Last year, Lonner published a study that showed the robot does this better.
Along with colleagues, he compared 31 partial knee replacements assisted by RIO with 27 traditional operations on similar patients with similar knee problems. With traditional surgery, Lonner found that the implant placement was off by an average of 2.7 degrees. But in his first surgeries with the robot, he was only off by 0.2 degrees. The results were published in Clinical Orthopaedics and Related Research.
On the market
Scientific studies on the efficacy of the hip tool are just beginning, Dorr says.
While RIO is designed to assist the surgeon, the Robodoc works on its own. It follows a pre-set program to drill a precise cavity for an implant while the surgeon stands by to observe and move muscle or other tissue out of the robot’s way.
The Robodoc, with an overhead drill and two spindly arms that hold the patient’s hip in place, was developed in the late 1980s and early 1990s (it was named around the time the 1987 film “RoboCop” was playing in theaters). Worldwide, doctors have used Robodoc in more than 24,000 hip and total knee replacements, according to the company.
Robodoc has been on the market in Europe since 1994 but was not approved by the U.S. Food and Drug Administration until 2008. The application, which Curexo made in 2007, was delayed in part by FDA concerns about a robot that acts on its own, Bargar says.
The FDA wanted to ascertain that the robot, as the first tool of its kind, provided as precise a fit and was as effective, in the long term, as manual surgery, FDA spokeswoman Karen Riley says.
Only one study, in the Journal of Bone and Joint Surgery in 2003, has shown complications with the Robodoc. Bargar thinks those doctors did not take care to prevent the robot from cutting soft tissues.
Curexo is now selling the robot for approximately $750,000, says Raymond Dimas, the company’s vice president of sales and marketing. So far, the one at Sutter General is the only one in the U.S. The company hopes to gain FDA approval for total knee replacements by the middle of next year, Dimas says. In the future, he adds, the robot might be useful for other bone surgeries, such as spinal operations.
In a 1998 study published in Clinical Orthopaedics and Related Research, Bargar reported that hip implants fit better overall in 63 people who were operated on by Robodoc than in 64 patients who had implants fit by hand. The team assigned a score of 1 to 5 to assess fit; the majority of Robodoc patients had top scores of 4 or 5 while manual surgery patients most commonly had scores of 2 or 3.
“No one can be as accurate as a robot can,” Dimas says.
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