“Patient specific guides aren’t ready for primetime, ” says Robert Barrack, “And being within three degrees…that probably doesn’t make a difference. “Wait, ” counters Mark Pagnano, “In a select subgroup of surgeons these guides are ready for primetime.”
This week’s Orthopaedic Crossfire® debate is “Patient Specific Cutting Blocks: Of Unproven Value.” For the proposition was Robert L. Barrack, M.D. from the Washington University School of Medicine in St. Louis. Against the proposition was Mark W. Pagnano, M.D. from Mayo Clinic in Rochester, Minnesota; moderating was William J. Maloney, III, M.D. from Stanford Hospital and Clinics in California.
Dr. Barrack: “I use these, and I think they have promise. But they’re not there yet. Variability in component alignment…in the short term it leads to complications; in the long term it leads to earlier revision. After 15 years, I don’t think navigation has had a major impact. The newer approach is patient-specific instrumentation (PSI). You get an MRI or CT, generate a model of the patient’s lower limb, and produce the patient-specific instrument, which actually is a cutting guide. All approved devices in the U.S. target neutral alignment, so they’re not patient-specific in that they all target the same alignment goal.”
“We’ve done a couple of studies that were just published, one on OR efficiency, one on accuracy and elimination of outliers. We used the same cemented CR knee in all cases. It’s over 200 knees, 100 in each group that are comparable, by a single surgeon.”
“With this component its posterior flange wedge holes allow the technician to center the holes on the flange to have neutral rotation for all postoperative measurements. We looked at a femorotibial angle with a target of five degrees, a hip-knee-ankle axis with a target of zero degrees, and a mechanical axis so that your neutral line passes within one zone of the center of the tibia.”
“The cost benefit analysis (CBA): We looked at all steps in the instrument processing; we timed every step, and we did a cost analysis of every step using our fixed hospital overhead. This is no doubt a simpler procedure. But four fewer instrument sets only translated into about $26 per case. The 12 minutes less in the OR did save about $300, but that’s a total of only $326 when the guides themselves cost almost $1, 000. MRIs…in this study the average dollars collected was about $1, 200.”
“One of the largest centers, the developer of this system in Columbus, Ohio, got their outliers down from 30% to about 15%. But does that make a difference? Does being within three degrees add any value? Mark Pagnano and his group demonstrated that if you’re close to that there’s no difference in survival among outliers.”
“Is neutral access really the ideal target for all patients? Probably not. A Knee Society Award paper showed that a third of men had constitutional varus; we’ve done a similar study using a new imaging technology, weight bearing 3D analysis on 200 normal knees. We showed that a third of patients are outside of this neutral mechanical axis. The real problem is that the joint line is oblique by about three degrees in a normal patient, so putting patients perpendicular to the joint line, to the mechanical axis, is changing their axis of rotation by up to eight degrees.”
“When imaging allows us to truly determine a patient-specific alignment, then there is a better chance we’ll be able to realize the benefits of this technology.”
Dr. Pagnano: “I’d like to focus on patient-specific total knee replacement (TKR) and look in particular at CT-based solutions. As Robert alluded to, computer assisted surgery hasn’t helped us in this area. Patient-specific instrumentation at least offers the opportunity to harness some of the gains of computer navigation, and take advantage of the advances in 3D reconstructive technology over the last decade.”
“Perhaps we move the computer part out of the OR. By doing that we may be able to save OR time and resources, but also save some mental energy so that we can focus on the soft tissue balancing parts of knee replacement. There are patient-specific instrumentation choices from multiple vendors and multiple differences between these. They differ in the alignment goals, the imaging modality, whether you get a pin guide or an integrated cutting guide, and whether that guide is all plastic or includes a metal cutting slot. There are also differences in the degree of surgeon input into the preoperative planning process.”
“CT-based data beats MRI data…it’s quicker, less expensive, you get more data, and you get real time alignment information. You get more detail from a 3D model created from a CT; that’s based on the physics…the image acquisition matrix for CT is twice that of an MRI.”
“The surgeon involvement…I think the thought process here is ‘Trust but Verify.’ You want the opportunity to review, approve, change, or redesign at any stage, if necessary. I’d rather use a cutting guide than a pin guide because you get the best accuracy and efficiency. And an integrated metal slot makes sense; surgeons are used to cutting through metal, so we’re going to get the most robust and accurate cuts. Blocks from any company give great contact against the bone, so why give that up and rely on two pins?”
“I think there is a role for these, and it’s for two separate groups of surgeons. For the high volume joint subspecialist…and then at the other end of the spectrum, a lower volume surgeon in a lower volume hospital.”
“The high volume surgeon can take that 11 minute gain in efficiency and turn that into an additional case in an operating day. That added volume is a key driver of lower cost for their institution. As for the lower volume surgeon, he may have a different OR team daily or a team that does general surgery, ENT, orthopedics. They use many vendors, so one day they’re doing a DePuy knee, the next a Biomet, etc. These patients are exposed to longer operative times. In this circumstance you can save 35-50 minutes per case, based on our data.”
“The cost depends on who you’re talking to. As a surgeon I ask, ‘Who am I responsible for?’ First, to the patient, so if these guides are going to help me either save time or be a bit more accurate then it’s useful. Second, my family…if I can get out of there a little quicker, that’s good. And finally, the hospital and the insurer.”
“The future for these instruments is going to come when we get size-specific, disposable instruments that simplify the setup and takedown; also, when the imaging technology is such that we get 3D models built from 2D plain radiographs.”
Dr. Barrack: “CT and MRI are too expensive; CT has high radiation. To go forward we’ll have to have lower radiation, lower cost imaging, and we’ll have to prove that this has some clinical benefit. I think we can, but we got through this first generation while we really didn’t have enough evidence. In the era of value-based purchasing and comparative effectiveness, we wouldn’t meet those standards today.”
Dr. Pagnano: “If you’re in an integrated system, if the hospital is charging for the CT or the MRI they’re potentially making money. That offsets some of the cost of a subsequent instrument that you’re buying.”
Dr. Barrack: “We know that the technical component…it’s a $1, 200-$1, 500 cost to somebody.”
Moderator Maloney: “So Mark, let’s say you and I are the payor and we’re going to be doing a million total knees in the U.S. We’re going to add $1, 500 per case…adding $1.5 billion to knee replacement. How to justify that?”
Dr. Pagnano: “People stood up here at these podiums in the 1990s and discussed demand matching of implants to patients. That didn’t go as far as we thought; we’ve had more and more expenditures. No question…if you take the whole system, this is adding cost. But when you say, ‘For a surgeon is it adding cost, for an individual patient is it adding cost, for a health system, the answer is different depending on the point of view.’”
Moderator Maloney: “But it is adding cost.”
Dr. Pagnano: “But for that surgeon who is doing 25 a year and saving about 39 minutes, that’s a savings also.”
Moderator Maloney: “To the surgeon personally.”
Dr. Pagnano: “But it’s his hospital system.”
Moderator Maloney: “That’s based on the fact that you’re going to either be able to add another case—which most systems aren’t able to do. Or you’re going to fire somebody, and you don’t usually have an opportunity to fire somebody because of cost savings in terms of time efficiency. Robert, what about meaningful clinical difference? In your group, it was a wash. Let’s say you’re getting two or three degrees more accurate—does that mean anything?”
Dr. Barrack: “No, I think the next big advance in knee surgery will be figuring out alignment. We have a huge range we’re shooting for—three to eight degrees. You should be able to predict who should be at three and who should be at eight, and we have the imaging technology to be able to do that. Then we have to prove that those patients will do better.”
Moderator Maloney: “Mark, we’ve all had a patient we’ve done bilateral knees on, started out with varus deformities, one we left in a little more varus than we’d like.”
Dr. Pagnano: “We’re still a fair distance away from being able to predict where someone should be. I think it’s that the dynamic aspects of gait are what drives the ideal alignment. It’s too simplistic to say that if you’re born in varus you should stay in varus. That may be true if you’re saying what’s going to give you the lowest amount of pain postoperatively or maybe the easiest range of motion. But what we’ve always battled in knee replacement is saying, ‘Well, that may be ideal for function, but does it have a penalty on durability?’”
Moderator Maloney: “Your data suggests that three degrees one way or the other, with newer materials, doesn’t really…well we don’t see bad poly wear anymore.”
Dr. Pagnano: “It’s one of those things where if you suddenly change the target for lots of patients then we must be aware…”
Moderator Maloney: “So what’s a meaningful clinical difference? The target is neutral anatomical axis; where is it, plus or minus two, three?”
Dr. Pagnano: “The problem all along has been defining it…”
Moderator Maloney: “Short answer!”
Dr. Pagnano: “The bell shaped curve…”
Moderator Maloney: “Leo, come take him off the stage. You’ve got to shoot for something in the OR, what is it?”
Dr. Pagnano: “There’s no question you should shoot for neutral mechanical axis.”
Moderator Maloney: “You’re measuring your X-rays postoperatively…what are you unhappy with?”
Dr. Pagnano: “I’m still aiming for zero, plus or minus three, but recognizing that if I hit four I can’t show scientifically that that makes a clinical difference in survivorship.”
Moderator Maloney: “Robert, what are you shooting for?”
Dr. Barrack: “We’re all shooting for the same thing. The point is that we know that some patients belong at three degrees and some belong at eight degrees. And we’re close to being able to predict that with these 3D weight bearing images.”
Moderator Maloney: “Robert said they’re not ready for primetime. Are they?”
Dr. Pagnano: “In a select subgroup of surgeons.”
Moderator Maloney: “Always hedging his bet! Thank you, guys.”
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