“It’s 2011 and we’ve got no proven benefit of computer assisted total knee surgery. And we’re well into the second decade of use, ” states Robert Trousdale. “Wait, ” says Arun Mullaji, “There are absolute pros to this. Intraoperatively we know that it helps alignment, but more importantly it helps balance the knee. And there is more.”
Computer Navigation in TJA: Thumbs Up or Down?
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Great Debates
This week’s Orthopaedic Crossfire® debate is “Computer Navigation in TJA: More Bother Than It’s Worth.” For the proposition was Robert T. Trousdale, M.D. from Mayo Clinic in Rochester, Minnesota. Against the proposition was Arun Mullaji, F.R.C.S. (Ed), M.S. of The Arthritis Clinic in Mumbai, India. Moderating was Thomas S. Thornhill, M.D. from Harvard Medical School.
Dr. Trousdale: “In 2011 we’ve got no proven benefit of computer assisted total knee surgery. That might be alright if it was a new technology, but we’re now well into the second decade of use.”
“There’s been a meta analysis looking at 11 level one studies—randomized controlled trials—and their conclusion was that, ‘Navigated knee replacement provides few advantages over conventional surgery. Its clinical benefits are unclear and remain to be defined.’”
“What has been demonstrated with the computer is that it’s a better tool to hit a specific target than manual instruments. The problem is that we don’t know what the right target is for each individual patient. And there may be factors other than mild malalignment that may be important for durability. But it’s a good tool for research information, and it can help us learn what the optimal alignment of a total knee replacement is.”
“Demonstrated negatives to computer assisted surgery (CAS): increased surgical times, increased cost, and an increased prevalence of specific complications. The fundamental premise of CAS is that it will improve our alignment for a large cohort of patients, and that is going to improve survivorship of our knee replacements. I’m not sure that’s been well shown.”
“As for the data looking at survivorship relative to overall knee alignment, the studies have been relatively poor…using short X-rays. And John Moreland’s was a review…not a great way to look at the mechanical axis. Mark Pagnano spearheaded this study, which had 399 knees and 275 patients.”
“Postoperatively, we broke down the patients into five zones: 300 [knees] were in the middle, 60 were in a bit of valgus and 35 were in varus. At 15-year follow-up we were unable to show any survival free of revision for any reason on postop alignment…any difference between the well aligned knees and the outlier knees. So the survivorship at 15 years—with revision as the endpoint—was the same. Survivorship, using aseptic loosening or wear osteolysis as an endpoint—again, no difference. The malaligned knees did the same as the well aligned knees.”
“This study told me three things: one, that there may be factors other than alignment that may be important for a 15-year survival. Also, total knees can do alright in the long term with mild malalignment. Lastly, we don’t know where the alignment should be in our total knee replacements.”
“Navigated knees can be tricky. In the OR we now have tracking devices, camera, additional OR traffic. I think the future of computer/robotic assisted surgery is going to be out of the OR. If you move the computer out of the OR it will save time and resources. And it will save your mental energy to do the important part of the operation which is the soft tissue balancing.”
Dr. Mullaji: “Let’s start with the cons. Does CAS take more time? Most surgeons don’t take a lot more time—0-5 minutes at most. There are two studies showing that most surgeons become time neutral within 20-30 total knees. We also have much faster software and much smarter hardware.”
“There are a lot of studies showing that there is a cost effectiveness to the use of navigation for total knee replacement. This is impacted by the hospital volume and the initial cost of the equipment. Is there a learning curve? There are two recent studies showing that when you take experienced versus novice surgeons or centers, there is no difference in accuracy, outcomes, or complications from the first case onwards. In my own series of nearly 1, 500 CAS total knee cases there has been no learning curve and you get very good results in terms of alignment.”
“Intraoperatively we know that it helps alignment, but more importantly it helps balance the knee. It also helps in the assessment that you’ve corrected the deformity. There are many papers saying that alignment is achieved with navigation. There is our own paper of nearly 500 cases where we’ve shown that navigation can reduce the number of outliers. And we’ve extended these over a much larger series, and we’ve reduced the outliers to under 8%.”
“It has particular value in the obese; you can’t really determine where the femur is, where the hip center is in these cases. There are two studies showing that in conventional surgery when you analyze these patients there are nearly 40% outliers with conventional methods…we can drastically reduce this with navigation.”
“You can verify your accuracy before and after you perform the cuts—you can’t do that with patient specific instrumentation. More importantly, it helps to reduce the number of femoral components which are internally rotated as compared to conventional surgery.”
“Soft tissue balancing: You can check your medial and lateral gaps, not only at 0 and 90 degrees of flexion, along with the alignment, but throughout the range of motion. Once you’ve achieved a rectangular extension gap, CAS can help to achieve an equal flexion gap. You can play on the computer screen, anteriorly or posteriorly shift the component, flex or extend it, up/downsize the femoral component, ensure your gaps are perfectly equal and then cut.”
“There is a study showing that if you have better aligned knees, the International Knee Scores are better, the SF-12 Physical Scores are better, as well as the SF-12 Mental Scores. Gait analysis studies have shown improved outcomes with daily activities when you use navigation versus conventional surgery. Moreover, you have reduced blood loss, a reduced incidence of fat emboli, and a reduced incidence of notching.”
“As for the long term, the main indication for navigation is to try and stem this rising tide of revisions. If you look at 60, 000 revisions performed across the U.S., 42% are due to mechanical causes…so alignment and stability do matter.”
“We’ve shown with radiostereometric analysis studies that there’s less tibial subsidence if you use navigation as compared to conventional means. And I’ve looked at my own revision rate for mechanical causes before we started using CAS (so in the last 1, 000 conventional total knees) and we had 15 revisions. Compare this to our first 1, 000 with navigation where we reduced it to just three revisions for mechanical causes.”
“When you combine technique with technology you have an unbeatable combination. People may tell you it takes time…find the time!”
Moderator Thornhill: “Thirty second rebuttal, Rob?”
Dr. Trousdale: “In specific circumstances a computer can help, such as with previous complex hip surgery or malalignment from trauma to the femur or tibia. Having said that, we don’t know where exactly to put the mechanical axis. We don’t know where the rotation of the femoral tibial component should be. Nor do we know where the balance should be. This is a tool that may help us get there, but in 2011 it’s not for routine clinical usage.”
Moderator Thornhill: “Arun?”
Dr. Mullaji: “We don’t know what the exact mechanical axis should be, but that’s not a fault of the tool. But if you have data as to what is the best axis to target I think there’s no better tool than navigation. Even if you want to go by the soft tissues and say, ‘This is how I want to balance my knee. I want to leave it in two degrees of varus, ’ then this is a tool that’s going to be able to get you there.”
Moderator Thornhill: “Rob, when would you use it?”
Dr. Trousdale: “I’ve used it for big deformities, I would use it for big varus bow of the femur/tibia. If you don’t have access to that then intraoperative fluoroscopy is not as precise as the navigation, but it’s certainly more precise that eyeballing the cuts and intramedullary guides. I’d have no qualms about intrapoperative X-ray either if I didn’t have access to navigation.”
Moderator Thornhill: “What would it take for you to use it routinely in the OR?”
Dr. Trousdale: “A lot of medicine for myself.”
Moderator Thornhill: “You’re on a lot of medicine, right?”
Dr. Trousdale: “It would have to be time neutral and efficient and show proven long-term benefits.”
Moderator Thornhill: “I’ve never seen—when I add equipment—that the cost remains neutral?”
Dr. Mullaji: “There are enough studies to show that if you factor in your hospital volume, your initial costs are not that high. The economists are saying that it is a very cost effective tool.”
Moderator Thornhill: “But aren’t they saying that it will increase your hospital volume?”
Dr. Mullaji: “I don’t think the studies are showing that, but if you have a large number of cases then your initial cost is reduced.”
Dr. Trousdale: “I think some of those make the assumption that it may decrease your revision rate. You’ve got to prove that before you can make that assumption. But on the front end it’s a more expensive technology.”
Moderator Thornhill: “Will we all be using some form of navigation in the future?”
Dr. Mullaji: “Yes, whether you’re going to be using navigation from home trying to figure out these cutting blocks or intraoperatively. I suspect that a lot of us will continue to use navigation for every case, especially as it gets more portable and the software is improved.”
Moderator Thornhill: “I’ve not used navigation, but I’ve been told that you’re not as good with soft tissues with navigation. If it’s a loose knee I put it in tighter than I would in a knee that is tight. Do you agree that you can balance the soft tissues as well?”
Dr. Trousdale: “With navigation?
Moderator Thornhill: “Yes.”
Dr. Trousdale: “I didn’t use it for soft tissue balancing. I just use it for sagittal and axial alignment. Arun, why don’t you think there is penetration in the U.S. and Canada with that technology if it’s that great?”
Dr. Mullaji: “It’s partly related to the perception people have that navigation is more cumbersome, more time consuming, and that it’s not easy to learn.”
Dr. Trousdale: “Every surgeon has different error points. Mine in total knee surgery appear to be on my tibial slope and that is where navigation did help me.”
Dr. Mullaji: “In our cases we have a lot of deformity in the femur…in the coronal plane…and this technology helps us put the distal resection at 11 degrees if necessary, something you can’t do with conventional surgery.”
Moderator Thornhill: “Thank you.”
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Discussion
This is a fascinating development. In my practice we've seen similar outcomes with the revised protocol. The key differentiator seems to be patient selection criteria. Has anyone else noticed the correlation with BMI thresholds?
Great point. I'd push back slightly on the conclusion, the sample size in the cited study is too small to draw population-level inferences. That said, the directional signal is compelling and worth a larger RCT.
We implemented a similar approach last year. Early results are promising but we're still gathering 12-month follow-up data. Happy to share our protocol if anyone is interested.
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