Leo Whiteside says, “Neutral mechanical alignment is the way to go.” Dunbar counters, “But in the future, a patient specific approach to knee implantation strategy is the future of TKA [total knee arthroplasty].”
This week’s Orthopaedic Crossfire® debate is “Straight and Balanced: Gimme That Old Time Religion.” For the proposition is Leo Whiteside, M.D. of the Missouri Bone and Joint Center in St. Louis; against the proposition is Michael J. Dunbar, M.D., F.R.C.S.(C), Ph.D. from Dalhousie University in Halifax, Nova Scotia. Moderating is Daniel J. Berry, M.D. from Mayo Clinic in Minnesota.
Dr. Whiteside: “The knee is so complex that nobody really understands it…just like the universe. Religion is often used to describe how it works, and people’s opinions on total knee replacement begin to sound like religion.”
“I speak to God a lot, sometimes loudly in the OR. The road to salvation is straight and narrow and you get there one step at a time. Excellence is expected…but not perfection.”
“This is how a good knee should work: as the hip and knee flex, the tibia stays in the AP axis and it rotates around the epicondylar axis. As you flex the knee you can see up the tibia, down through the AP axis of the femur and right to the femoral head. A good knee is a little looser laterally than medially in extension; in flexion it’s a bit looser than in extension and looser laterally than medially.”
“The way to do this is bone landmarks aligned separately in flexion and extension with tight ligaments released based on function. Then you cut by the pre-valgus angle of the femur, perpendicular to tibia. The AP axis of the femur is your alignment landmark on the femur, on the bone, in the knee. Stay on the bone and out of trouble. For matched resection, resect the thickness of the implant from the intact surface and that gives you a knee that is balanced in flexion and extension.”
“Let’s look at a varus knee. You find a reliable landmark such as the AP axis. Down the center of the canal we make a hole with the reamer and ream down the cement center of the tibia as well. And you must aspirate the medullary canal of the femur. Then the intramedullary rod is inserted. The AP axis marks the femur in flexion; the intramedullary rod is inserted into the tibia down to the ankle. You make cuts based on the medullary canal, and you correct the deformity. Then, osteophytes are removed, the tight ligaments are released, and you stabilize it with a thicker polyethylene.”
“It’s similar with a valgus knee. The tibia is outside the AP plane; you’re going to put it in the AP plane by following the AP axis. When you hold the leg straight, the AP axis is perpendicular to the floor. That is going to correct the deformity on the femoral side. You put the medullary rod in and cut based on the intact surface—even if there is a defect left on the lateral side. Then apply the cutting guides, which are aligned relative to the AP axis. Then you finish your cuts, correcting deformity on the femur based on the AP axis of the femur; you put the intermedullary rod on the tibia.”
“Now it’s loose medially in flexion and tight laterally. And we have a complex series of ligaments to deal with. You do a gradual release from front to back for flexion on the epicondyles, which creates partial correction. And finally the epicondylar release. The posterior/iliotibial band gives a knee that is correct in flexion and extension.”
“Rule number two is that the road to hell is paved with good intentions…and I mean tensioners, constitutional varus, magic instruments that eliminate ligament balancing, navigation, bogus Internet advertising, and taking money for doing nothing. Then God Almighty will show up at your office in the person of plaintiff’s attorneys, angry patients, and the Department of Justice.”
Dr. Dunbar: “Bless me, Father Leo, I have sinned. I no longer follow the tenets of the gospel that has been laid out. While a neutral mechanical axis is still the gold standard until proven otherwise, it won’t be the gold standard for all patients in the future.”
“Why do we stick to a neutral mechanical axis? The most widely quoted paper in recent literature is the 1991 paper from the UK with 115 Denham knees followed up from 1976-1981 and using an intramedullary alignment. The participants were mainly female and about half of them were rheumatoid patients. They found that if you left the knees in neutral only about 2.5% of them failed; if they were more than 3 degrees of valgus then 12.5% failed. If they were greater than 3 degree of varus then 33% failed.”
“The prosthesis used in that study is obviously not what we are using today. This had a 7 degree fixed valgus angle on the femoral component. The process was to drop the intramedullary rod in while you cemented the tibial component and then shave it with a pair of shears.”
“The most important argument as to why we need to consider an alternative to neutral mechanical alignment is the fact that around the world the number of patients dissatisfied with their knee replacement is 18% (the UK, Sweden, and Canada). It goes back to the basic epidemiology we learned in grade school about frequency distributions in populations. So as we take the straight and balanced approach we are covering the majority of the curve, but missing the tails—those who are never in neutral mechanical alignment, and who don’t like being in neutral mechanical alignment.”
“An important paper by Johan Bellemans, M.D., Ph.D. et al, spoke to this. They studied 500 healthy individuals in their twenties, and they looked at them with long length standing films. It turned out that on average, the alignment of this group is 1.3 degrees varus. Broken down by gender, 1.9 degrees varus for males and 0.8 degrees of varus for females. A full 32% of the males were greater than three degrees of varus; 17% of women were greater than three degrees of varus.”
“Despite this, we stick to the tenets of St. Leo and decide that even though only 2-3% of the population has a tibia that’s neutral to the floor, we must do a neutral cut on the tibia. And once you do that you must make a compensatory gap in extension where you take asymmetrical cuts. More importantly, in flexion we have to go through machinations to rotate this femoral component in a position it wasn’t meant to be in so that we can balance this flexion/extension gap. Perhaps if you don’t follow this tenet, and you do put the components where they perhaps should be in other than Leo’s alignment, then you may not have to do these releases.”
“In 2011 at this conference Adolph Lombardi said, ‘Although technology has improved surgical precision, it has not eliminated the human factor, and aiming for neutral provides the safest margin for error. The foremost objective of TKA is a durable and well-functioning joint, not necessarily one that replicates normal or the patient’s native condition.’ This is what patients are complaining about. They say their knee doesn’t feel normal and we told them, ‘Too bad because you’re in neutral mechanical alignment and your X-rays look good.’”
“The renaissance is a 3D perspective. There are different morphological variations of femurs that we’re operating on daily, and we don’t compensate for this as we approach. Another blasphemous tool that I’m keen on is navigation, which shows us that patterns of alignment through range of motion (ROM) are important. Normally, when we approach a varus knee we think that it’s varus through ROM, but after looking at thousands of these we know that some patients start in varus and by the time you flex them they’re into valgus.”
“Lastly, there are two different kinds of outcomes. In the St. Leo tenet you take an unstraight knee and after your cuts they are straight. But there’s a compelling example of other types of patients who have this sinusoidal morphology…and after you’ve operated on them, wittingly or unwittingly, all you’ve done is shift their curve. They have kept the same morphology. In the end, a patient specific approach to knee implantation strategy is the future of TKA.”
Moderator Berry: “Is this just an esoteric argument or are we just not good enough to measure it yet?”
Dr. Whiteside: “The study from Merrill Ritter’s group shows that a knee that is significantly out of alignment does much worse than those within a reasonable level. Sometimes five degrees of mechanical axis of varus is not easy to detect by eye. The Mayo Clinic study suggests that three degrees of varus or valgus mechanical axis malalignment is alright. I agree, but remember that three degrees is 1.5 on the femur, 1.5 on the tibia. If you can get more accurate than that you’re better than I am.”
Dr. Dunbar: “It’s not an esoteric question at all. The renaissance is all these tools (4D assessment, gait analysis, etc.). Merrill Ritter’s paper looked at short, 2D films—a 110 year old technology.”
Moderator Berry: “So Mike, you think that eventually we’ll be able to do better and we will be able to individualize optimal implant position, balancing, and alignment? Is it also fair to say that right now we don’t know how?”
Dr. Dunbar: “Yes, that’s why I started my talk by saying that neutral mechanical axis is the gold standard.”
Dr. Whiteside: “I love you computer/navigation guys and I can’t wait for you to come up with something that we can use.”
Dr. Dunbar: “I don’t know what to do with the data, but it is compelling that there are differences between the patients. I imagine that pilots had this argument 25 years ago: ‘There’s no way that computer is flying my plane!’ But no pilot would be allowed to take off if the computers weren’t working. Not because the pilot can’t fly the plane, but because the margin of error goes down and outcomes improve.”
Moderator Berry: “Everybody’s emphasized the importance of proper femoral rotational alignment. Leo, when you’re doing the AP axis of the femur; are there any ways you can get fooled?”
Dr. Whiteside: “By trying to use deformed anatomy to adjust your line. Center the intercondylar notch posteriorly and if you have to, remove the osteophytes. The deepest part of the patellar groove just above the intercondylar notch…use that as a basis to make your line further anteriorly and ignore any deformity in the patellar groove.”
Moderator Berry: “If the patella has eroded the trochlea does it mess it up?”
Dr. Whiteside: “It does not because that deepest part of the groove is still there.”
Moderator Berry: “Mike, how do you set your femoral rotation?”
Dr. Dunbar: “I do it off the navigation and trying to get equal resections posteriorly off the femoral condyle.”
Moderator Berry: “Thank you both.
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