Barrack V. Stulberg: Head to Head Over Cutting Blocks

When it comes to patient specific cutting blocks “Radiographically we could not prove a benefit, ” says Robert Barrack. In fact, “we were slightly better with standard instruments than with the custom specific, patient specific instrumentation (PSI)”. The epidemiology of revisions is troublesome, says David Stulberg, so “PSI deserves a careful look because there is a clinical advantage. The costs will come down.”

This week’s Orthopaedic Crossfire® debate is “Patient Specific Cutting Blocks: No Added Value.” For the proposition was Robert L. Barrack, M.D. from the Washington University School of Medicine in St. Louis. Against the proposition was S. David Stulberg, M.D. of Northwestern University in Chicago. Moderating was William J. Maloney III, M.D. from Stanford Hospital and Clinics.

Dr. Barrack: “Variability in component alignment continues to be a major issue in total knee arthroplasty (TKA). In the short term it can cause persistent pain and dissatisfaction. In the longer term, it can contribute to every mode of failure. After a decade of clinical use I think that navigation isn’t going to be the answer.”

“A new approach: patient specific guides in which you do an MRI or CT and generate a model for each patient’s lower limb to produce the patient specific instrumentation [PSI]. Almost every company has some version of this. I’ll speak about the Biomet Signature.”

“The goals of the patient specific approach are to increase accuracy, to customize instruments for the patient, and to eliminate outliers. Secondarily, we want to get more efficient and lower the total operative time and cost. We did a series of studies—about 114 cemented cruciate-retaining knees, and we used coronal alignment assessment with a scout CT.”

“We have 57 in each group who successfully completed the scout CT and had analysis. The femoral component has a posterior flange that has wedge holes that allow you to reference so you can accurately locate the limb to get reproducible alignment.”

“We did a careful assessment of coronal alignment: femorotibial angle, Hip Knee Ankle Axis, the Zone of the Mechanical Axis, and the mechanical axis deviation. The femorotibial axis is typically between two and seven degrees. A long film is utilized to measure the Hip Knee Ankle Axis—center of the hip to the center of the knee through the center of the ankle. In a perfect case it’s zero degrees.”

“The Zone of the Mechanical Axis is where that line crosses the center of the component, and it should be in the central zone if you divide the tibia into five zones. We also measured the number of millimeters that we deviated from achieving this central zone. We determined the total tourniquet time and the total time in room between groups. All steps in instrument processing were timed utilizing industrial efficiency methodology. These times were converted to cost of materials, personnel, and fixed hospital overhead, including the time in the operating room.”

“Customized knees have about half the number of trays, and every step of the process was much quicker, so you do save money on the sterile processing cycle. But when you do this in large volumes, the cost saving is not as much as we had thought. It was only about $26 per case in fixed overhead for the hospital; the bigger savings was about $300 in saved time in the OR per case.”

“Radiographically we could not prove a benefit. We were just as good with standard instrumentation; in fact with the Hip Knee Ankle measurement we were slightly better with standard instruments than with the custom specific, patient specific instrumentation. So we couldn’t prove an advantage in a coronal alignment.”

“There are limitations. We didn’t measure the lateral view, rotational alignment was not assessed, clinical result and patient satisfaction were not measured; we have a randomized clinical trial underway to see if the patients do better because of more accurate and consistent rotational alignment, and possibly lateral alignment.”

“The cost-utility analysis—although we saved $300 per case the guide itself costs anywhere between $500-$1, 000…and then there’s the imaging cost. I will say that there’s a high acceptance among patients, the OR staff, the processing personnel. But right now, the cost benefit is hard to justify in the absence of demonstrated radiographic or clinical advantage.”

Dr. Stulberg: “The number and cost of revision TKA are increasing in the U.S., and the epidemiology of revisions is troublesome. Many of them occur very early, often within the first two years; a very high proportion of these are a result of inadequate surgical technique. The goals of navigation are to emphasize the importance of accuracy in attempting to deal with this issue. While navigation is focused on an alignment in the coronal plane and reducing outliers, its biggest goal was to reduce the number of inaccuracies in each step of the operation.”

“Navigation has not been very helpful for inexperienced/nonarthroplasty surgeons. It’s too expensive, it requires clear understanding of total knees, it requires a significant learning curve, and it uses cumbersome instrumentation.”

“My interest in this emanated from the idea that if PSI technology increased the accuracy and reduced the outliers for surgeons who weren’t arthroplasty surgeons, that maybe the reduction in cost associated with that improved accuracy—in association with the improved efficiencies that go with this technology—might offset the increased cost. The question is, ‘How accurate is this technology?’”

“Navigation is an accurate measurement tool that could be used to look at this technology. We tried to look at each step of the operation to see how accurate this technology was…because there is very little data on it. My arthroplasty partner, Raj Ghate, and I looked at our first 111 total knees using this technology…the first 31 of which I did I used computer assisted technology. We also looked at how accurate PSI planning program was in predicting the size of the femoral component, and comparing that to the accuracy of computer assisted surgery in predicting femoral component size. We also measured all of our bone resection to see whether it matched the preoperative plan. We looked at the positioning of the femoral component, both with regard to anterior/posterior positioning, as well as rotation.”

“The results: the coronal alignment is ‘on’…and if this were the reason you were using PSI technology I’d suggest it isn’t worth it because you can achieve this without really going to PSI technology. The PSI technology gives very accurate coronal and sagittal alignment—even on the tibia, which is harder to use when you’re starting this, and which we would recommend using an external guide when you’re placing that initial PSI guide.”

“Still, it was extremely accurate in the frontal and sagittal plane. But the money is here: the PSI predicted femoral component size virtually every time (92% of the time versus 43% with computer assisted technology. Moreover, the PSI technology tends to place a component dead-on in the anterior/posterior (A/P) plane…and it positions it very accurately in rotation as a result of the preop plan using accurate anatomic landmarks. So if you’ve got a precise femoral size and you have precise A/P placement and precise rotation then you have the makings of a very accurate flexion gap.”

“PSI deserves a careful look because there is a clinical advantage. The costs will come down. The PSI technology focuses our attention on making TKA more efficient and cost effective. The financial benefits of reducing revision rates must be included in any cost analysis.”

Moderator Maloney: “Robert, a minute to rebut.”

Dr. Barrack: “The buzz words we’ll be hearing are value-based purchasing and comparative effectiveness. And when we introduce an expensive new technology we must be able to produce data showing that it accomplishes something. We’re still dealing with early generations. We are arthroplasty specialists, so this may do better in the hands of less experienced surgeons. But you don’t want people to become totally dependent on this because if they don’t get a great fit with their cutting block then they won’t have the experience to bail themselves out.”

Moderator Maloney: “David?”

Dr. Stulberg: “We’re just beginning to understand the impact of this kind of technology. There are other ways of achieving fewer instruments in the room and faster turnover. The kind of efficiency embodied in this first generation is going to be the way we go; add that to an accurate technology that’s user friendly and efficient, then you’ve got a winner.”

Moderator Maloney: “Robert—sources of error…one of them is that the surgeon must approve the preoperative prescription. How cumbersome is that?”

Dr. Barrack: “It adds 10/20 minutes. You look at the cut plan and see if it makes sense.”

Moderator Maloney: “You said the overall time savings was in the OR, but what about when you add the preoperative planning phase? Does that make the time a wash?”

Dr. Barrack: “No, because it’s web based…you can go online anywhere in the world and make sure it makes sense.”

Moderator Maloney: “What’s the time lag from the time you get the scan to the time can actually get the implants?”

Dr. Barrack: “Four weeks.”

Moderator Maloney: “David, is computer assisted total knee arthroplasty a dead horse?”

Dr. Stulberg: “No, it’s not dead.”

Moderator Maloney: “Is it on life support?”

Dr. Stulberg: “It’s relegated to a small volume of what we do.”

Moderator Maloney: “Robert, as for the cost, you’re adding on somewhere between $1, 000 and $2, 000 for the scan. I suspect the system/Medicare won’t look upon that positively.”

Dr. Barrack: “The cost of the plastic itself—I think it will come way down. Although there is some software planning—a technician has to review and generate…”

Moderator Maloney: “When you send a patient for an MRI for a total knee replacement, what do you use as a preop diagnosis? Osteoarthritis isn’t something typically that they’ll accept as a reason to get an MRI or a CT.”

Dr. Barrack: “You’d be surprised. They will.”

Moderator Maloney: “They must not be looking at this very carefully yet. David?”

Dr. Stulberg: “If you put down ‘preoperative planning, ’ that will be the catch word—at least for United Health. My view on it is that most surgeons don’t do very good preoperative planning anyway…and they do it on a technology—X-rays—that is highly inaccurate. Now we have a very accurate imaging tool and the preop plan that you get back is probably much better than most of us would do.”

Moderator Maloney: “I would agree. David, you stated that the rotation alignment was significantly better with the PSI, but there was no data up there. Did you measure that or was that a hypothesis?”

Dr. Stulberg: “CT would be one way to look at it. We looked at it with Whiteside’s line as our preoperative alignment guide and we matched that with an intraoperative assessment.”

Dr. Maloney: “So that was a guesstimate in the OR. Robert, how do we measure rotational alignment and should we?”

Dr. Barrack: “We’re doing it clinically. Patients don’t care if their components parallel the epicondylar axis…they care if they have stiffness or pain. The corollary is that if you’re right on with the position then they should get their motion back quicker, and they should have less residual symptoms.”

Dr. Maloney: “So you’re not objectifying that with a CT scan to look at the rotational axis?”

Dr. Barrack: “No. We all know that the secret among arthroplasty surgeons is that 20-30% of patients aren’t crazy about their knee—and I think that they are most likely malpositioned.”

Dr. Stulberg: “Intraoperative assessment: one way is by seeing whether the measured cuts are actually what was predicted because that will tell you whether you’re close. The other is to use an intraoperative sensor to see whether you’re balanced.”

Dr. Maloney: “That doesn’t tell you whether you’re actually matching the rotational axis that you were shooting for. Thank you to both debaters.”

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