A cut above

From the September 26, 2004 issue of the Roanoke Times.

A new computer system at Carilion Roanoke Memorial Hospital means better knee surgery … and longer-lasting knees. trtlogoIt’s a good thing Lois Stafford is unconscious. She probably wouldn’t want to hear what Dr. Joe Moskal is saying as he’s operating on her knee. “Can I get the wrench, please?” he asks at one point. And besides the usual surgeons’ requests of “scalpel” and “clamp,” Moskal asks for a “mallet,” “drill, ” “saw” and “rasp.” Moskal is an orthopedic surgeon, and he’s performing an arthroplasty, otherwise known as a total knee replacement – one of about 400 he does every year. More than 200,000 “TKRs” were performed nationwide in 2003, most as the result of osteoarthritis – when the knee simply wears out as the bones rub against each other. This is what happened to Stafford, 69, who had already undergone arthroscopic surgery and steroid injections for her knee, but only got temporary relief. Doctors decided that a replacement was her best option. What makes Stafford’s surgery noteworthy is not the low-tech part – drills, saws and wrenches – but the high-tech machine that’s guiding Moskal in using them. It’s called the Ci System, and it allows Moskal to create an electronic map of a patient’s knee and leg. That map lets the system’s computer guide his cuts more precisely than ever, giving a better fit and a longer-lasting knee. “There’s a ton of literature that says your longevity improves the better your alignment is,” Moskal explained. That’s common sense: Just as ill-fitting shoes soon begin to hurt, an ill-fitting artificial knee will have more friction and wear out sooner. The difference between a good fit and a bad one is tiny – we’re talking fractions of an inch here – but those fractions make a huge difference down the road. “If you can go from 90 percent accurate to 95 or 96 percent, you’re going to really improve your result,” Moskal said. That’s important, considering that a typical knee replacement may not last more than 15 or 20 years. According to Moskal, the 10-year success rate is about 95 percent, but that drops to 90 percent after 15 years. And those figures are becoming less accurate as younger people get new knees. They’re living longer and they’re putting more pressure on their knees, Moskal explained. “What will last 15 years in a 70-year-old may not last 15 years in a 40-year-old,” he said. That leaves doctors thinking about their patients’ ages from two sides: A younger patient will wear out a replacement knee faster, and an older patient – someone in his 50s – might need another operation when he’s in his 70s or 80s. And with age comes danger. The $170,000 Ci System makes some of those choices easier. Developed by Johnson & Johnson subsidiary DePuy, it debuted at Carilion Roanoke Memorial Hospital in April, and Moskal has already completed more than 30 procedures using it. Each costs between $21,000 and $53,000, according to Carilion spokesman Eric Earnhart. And yes, they’re covered by Medicare and most private insurance plans. Advances in medical technology are often blamed for raising health insurance costs, but this procedure is no more costly than the one it improves upon, Earnhart said.

When ‘good enough’ isn’t

In essence, a knee replacement is simple, although not something the squeamish want to think about. The two bones above and below the knee – the femur on top and the tibia below – meet at a ball-and-socket joint: the knee itself. (It’s also covered by a third bone, the patella or kneecap.) To replace a knee, the surgeon saws off the ball, saws off the socket, shapes the ends of both bones and the kneecap, and inserts a metal ball and socket as a replacement. The problem is that there’s no such thing as a standard knee. Every one is different, as is the shape and curvature of everyone’s leg bones. So not only is there no one-size-fits-all artificial knee, the best placement of the parts will depend on a lot of factors. It’s easy to install a knee replacement that’s almost right. Without the computer’s help, a surgeon would make an educated guess based on basic measurements of the patient’s anatomy, then try to fit the new parts based on the average. In some cases – people whose bodies were far enough outside the center of the bell curve – the patients would find their new knees not lasting long, or their range of motion reduced, Moskal said. The goal of the system is to take some of the guesswork out of the placement of the artificial knee joint, thus giving a better and longer-lasting fit. “It’s like the difference between flying an airplane with or without instruments,” Moskal said. “It’s able to tell us the exact size [replacement] to use, the position, and any deformities.” Carilion is now the only hospital in the Roanoke Valley using the Ci System, although Edward Murphy, the company’s president and CEO, said, “It’s not about being competitive. We try to make investments in technology that will truly improve and enhance patient care, because that’s our mission.” Although computer assistance doesn’t add to the cost of an operation, it does add significant time – time spent getting the placement exactly right. But, although it might require a patient to spend a half hour or more under anesthesia, Moskal said, “I’ve never had a patient tell me to hurry up.”

Tool time

Once Stafford is unconscious and her knee is prepped and opened, Moskal must first attach two “arrays”: one each above and below her knee. Sticking out of these, like tiny antennas, are three special reflectors that look like the ball inside a computer mouse. A few feet away, a computer with an infrared emitter is able to see the positions of those arrays to within a fraction of an inch. Using a drill that’s almost indistinguishable from one you’d buy at Lowe’s – were it not for the stainless-steel sheen – Moskal attaches these arrays to Stafford’s tibia and femur. Because they’re firmly attached to her leg bones, these will serve as points of reference for the rest of the procedure. At the computer, Richard Nichols, a technical sales representative from DePuy, verifies that the system is sensing the arrays properly. (Someone from DePuy is present at every operation involving the Ci System to assist the surgery team.) The computer needs to know the exact shape, size and position of Stafford’s knee bones. To do that, Moskal uses a pointer – also sporting reflective balls – to tell it the location of some specific points, following instructions from the machine such as “Pivot [the] pointer at the most medial part of the tibia.” On the screen, an animated image of Stafford’s knee begins to take shape as Moskal virtually “paints” the bones. “The [surgeon] picks the points and it morphs into a representation of the patient’s knee,” Nichols said. “It has a huge database of knees,” he explained, and it compares those to what Moskal is telling it about Stafford’s. Once the Ci System has a complete picture, it then consults another database: one of knee-replacement components. Just as you can get a number of different tires for your car, there are several brands, models and sizes of artificial knees. But only one is likely to be the best fit. “The software knows the exact specifics of the components; it tells you exactly what to use,” Nichols said. In Stafford’s case, it recommended a DePuy pfc Sigma Rotating Platform, size 2.5; Moskal has the option of concurring with this or telling the computer he wants to use something else. (He concurred.) Then comes what’s arguably the greatest benefit of the Ci System: It displays, in color and 3-D, exactly where Moskal should place his cutting guide (what woodworkers call a jig). Without the computer’s help, Moskal would have to make a best guess. Although his experience means that guess would be a pretty good one, the computer allows him to be even more accurate – to within a millimeter or less. The Ci System displays the position the jig should be in along with its actual position. Carefully watching the screen, Moskal has to move his jig (its position is indicated by a yellow disk on the computer’s display) to match the computer’s calculated best position (indicated by a blue disk). This means making tiny adjustments in three dimensions, which is one of the most time-consuming – and critical – phases of the procedure. Eventually the blue and yellow disks are aligned, and the cutting jig is clamped down. Minutes later, the room is filled with an acrid tang as Moskal saws off the end of Stafford’s tibia. He checks with the computer to make sure the cut was accurate. Once assured, he repeats the process with her femur. Then both ends, and the kneecap, are cleaned and prepared to have the implant attached, and a hole is drilled deep into her leg bones to mount it. Moskal first fits the sides of the implant without attaching them, the way you might hold a picture on a wall before deciding where to put the nail. He tests their position and carefully moves Stafford’s leg to ensure she’ll have the right range of motion. Satisfied that the implant will fit correctly, one of his team members mixes a special cement that will hold it in place. The implant is then cemented in place, checked again, and the incision is closed. Recovery time for a total knee replacement can vary widely. What’s certain is that Stafford will require physical therapy both in the hospital and at home, as well as medications for pain, inflammation, and to prevent infection. But the end result is likely to mean a shorter recovery and longer-lasting knee thanks to the computer assistance her surgeon received.