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.