Sculco v. Nam: Neutral Mechanical Alignment: Stickin’ With the One That Brung Ya

This week’s Orthopaedic Crossfire® debate was part of the 18th Annual Current Concepts in Joint Replacement® (CCJR®), Spring meeting, which took place in Las Vegas. This week’s topic is “Neutral Mechanical Alignment: Stickin’ with the One That Brung Ya.” For is Peter K. Sculco, M.D., Hospital for Special Surgery, New York, New York. Opposing is Denis Nam, M.D., Rush University Medical Center, Chicago, Illinois. Moderating is Thomas S. Thornhill, M.D., Brigham and Women’s Hospital, Boston, Massachusetts.

Dr. Sculco: Just to start off saying that I’m honored to be debating Denis Nam. We were co-residents to together at HSS and he was my chief resident. I think we’ve aged pretty well over the past few years. I consider Dr. Nam to be a research friend and colleague but today he is my CCJR foe and he is a formidable opponent because he has already won awards from Seth and already debated in previous debates and honed his research skills.

I am sure many of you look at me and think that I have met my match and that I am out brained and out brawned, but I would contend that I will win due to the fact that I am supporting mechanical alignment and he will fail due to the kinematic alignment weakness of his argument.

What are the keys to a successful total knee arthroplasty?

First, you need long term implant survival. Then we need improved function and overall quality of life.

Recently, there’s been growth in alignment paradigms and today we are going to focus on neutral mechanical alignment and kinematic alignment.

When we look at neutral mechanical alignment and we look at large, long term studies from various registries, we do have good 10-15-year data showing greater than 90-95% survivorship for a number of different total knee implants.

In terms of pain and function, there was a recent meta-analysis (Shan, JBJS-Am 2016) looking at a number of studies that showed that neutral mechanically aligned total knees have a large and sustained positive effect on improving pain and function in patients and are very effective in treating knee osteoarthritis.

So, you are probably, wondering why are we even having this debate today? What’s the problem with our current methods?

Of course, we have that 10-20% patient dissatisfaction and Denis has published previously that while 90% of patients are satisfied, only 66% of them thought their knees felt ‘normal.’ While we know that patient satisfaction is a multifactorial, very complicated problem that is not always related to the knee itself, it does raise a question whether neutral mechanical alignment could be contributing to this dissatisfaction.

For a patient who is potentially unhappy with his neutrally aligned total knee we have Dr. Howell. He believes that kinematic alignment is the answer to this patient’s problems. Why is it the answer? It corrects the knee to its pre-arthritic alignment, restores the native articular surface, the native joint line obliquity, the native joint laxity, and minimizes soft tissue releases.

But what is the penalty for doing this?

The problem is that the alignment from the hip, knee, and ankle axis is secondary to restoring their pre-arthritic alignment, so you have to put a tibia in varus and a femur in valgus. This could be somewhat concerning.

Does alignment matter for total knee survivorship and is there a penalty for placing your knees outside the “safe zone”?

Mayo Clinic had a marquis paper in 2010 in JBJS-Am (Parratte, et al) which looked at the +/- 3-degree safe zone and the long-term outcomes for 398 cemented total knees. They reported no difference in survivorship at 15 years for total knees outside the “safe zone.”

But then you look a little closer, 91% of patients were within +/- 4 degrees and there were fewer than 20 patients who were in varus overall alignment. I think we should caution making broad generalizations on the risk factors of the safe zone when we have less than 20 patients.

In a study of over 3,000 patients (Berend, et al, CORR 2004), it paints a slightly different picture. Looking at the effects of putting a tibial component in >3 degrees varus, it results in a 17 times increased risk of failure over time and when you combine varus with a BMI greater than 33, which is many of those patients in the U.S., the failure rate goes up exponentially (168x).

There are multiple papers; historically, we have seen an association between varus alignment and total knee failure. You have a meta-analysis (Liu, et al., Knee Surg Sport Traumatol Arthrosc 2016) with more contemporary knee designs of over 12,000 knees showing that varus overall alignment shows a higher rate of failure. Alignment matters for survivorship.

Looking at retrieval data (Collier, JBJS-Am 2007 and Werner, J Biomechanics 2005), there is increased polyethylene wear when knees are in varus even when hips, knees and ankles are in neutral. Alignment matters.

Looking at finite element analysis data (Innocenti, J Arthroplasty, 2016), tibias in varus have 45% increased stress on medial bone and having a varus tibial component is always detrimental. So, alignment matters.

Cadaveric studies (Green, J Arthroplasty 2002); you place your tibial component in varus, you load your knee with a tester and you have a posterior-medial hotspot and that classic posterior-medial collapse. Alignment matters.

So, why is Dr. Howell still smiling?

Because in his one long-term outcome study of 233 kinematic knees at 6.3 years, his knees perform extremely well—97.5% implant survivorship at 6.3 years even though 80% of those tibial components were in varus, some of which were up to 7 degrees.

But, at 6.3 years in the other varus studies presented, those knees, also in 3 degrees of varus, were performing exceptionally well.

I would say that Dr. Howell’s patients are right at the point of a potential change, which means a ticking time bomb.

In conclusion: long term implant survival…neutral mechanical alignment is guaranteed with good data. Kinematic alignment is unknown; it could be a ticking time bomb. There is no difference in function in a well-controlled randomized controlled trial so in 2017 neutral alignment is the gold standard. Kinematic alignment requires continued close surveillance; additional testing, new implant development and limited adoption until more data is available.

Dr. Nam: It’s an honor to be debating Peter Sculco. He stated that we were residents together and his dad is one of my mentors, so I apologize to the Sculco family for taking you guys down today.

I think Peter gave an excellent talk and there is not a lot I can disagree with there. But I think it is important that we push forward and question the norm. We should ask what we’ve been doing over the last few decades and whether or not it is actually good enough. Are total knee replacement outcomes good enough?

I would argue that we are not doing a good enough job to get consistent patient satisfaction.

Doesn’t neutral alignment improve outcomes? I would argue that studies show it does not necessarily guarantee a good outcome after knee replacement.

I question why we should be making every knee look the same. This principle never made sense to me even when I was learning to do a knee replacement during residency and fellowship. We have varus knees, we have valgus knees, and we have severe contractures, yet we are still trying to shoot for the same target for everyone.

Peter already mentioned that 19% of patients are not satisfied with their outcome after knee replacement. There are numerous other studies that have shown similar dissatisfied results. Does improved accuracy increase improved survivorship? Well, Peter also mentioned this study (Paratte, et al., JBJS-Am, 2010) from the Mayo Clinic, where he did his fellowship.

And recently, Matt Abdel published the 20-year results of this cohort which showed no difference in survivorship looking at aligned versus outlier knee replacements relative to a neutral mechanical alignment. There is no difference in 15-year survival based on achievement of a neutral mechanical alignment.

I will not argue that alignment does not matter. But I do argue that trying to fit people into this dichotomous box of neutral or malaligned is kind of a ridiculous target when looking at knee replacements.

Does improved accuracy improve clinical outcomes? Well, I don’t think that’s the case.

We have seen where neutrally aligned knees do not do well. I think we would all agree that computer navigation improves alignment accuracy. But have we been able to show that computer navigation therefore improves clinical outcomes? I would argue that that is not the case.

A study out of Korea (Kim, et al., JBJS-Am, 2012) was a prospective randomized trial of 520 patients undergoing bilateral knee replacement. One knee had computer navigation, the other with conventional instrumentation, all targeting neutral alignment. They had similar survivorships of 98% and 99% between the two cohorts for mechanical loosening at 10 years and they had no difference in knee function, pain, and WOMAC scores.

Do new implant designs make a big difference?

We looked at 527 total knee replacements from 4 centers (Nunley, et al., Knee Proceedings 2014). They were all administered as a telephone survey from a third party, blinded, independent center. We found no difference in patient satisfaction or symptoms with new implant designs such as high flexion, gender-specific, rotating platform versus an old design (10-year cruciate retaining).

What are some of the newer alignment concepts? Well, we talk about constitutional varus, and Johan Bellemans, et al. (CORR, 2012) found that 32% of men and 17% of women have a natural, mechanical alignment of greater than 3 degrees at skeletal maturity. About 2 degrees of valgus of the distal femur and about 3 degrees of proximal tibia varus is their native alignment and thus, they hypothesize that a neutral alignment will be unnatural in a significant proportion of patients and to me that concept makes sense. You’ve been in varus your whole life, if you get corrected to slight valgus or neutral maybe that’s not going to feel normal for you.

In a retrospective study by VanLommel, et al. (KSSTA, 2013), 132 patients with a preoperative varus deformity were followed for a mean of 7 years. Researchers found that patients with mild varus had improved Knee Society scores with no impact on survivorship at that time point. I agree this is a midterm report and we need longer follow up, but a lot of the data that Peter showed are on older implant designs that may not show these same types of results.

Kinematic alignment…where the goal is to align and set the joint line to that of the native knee is another new concept. In these cases you’re building off of the femur and whatever your overall mechanical hip-knee-ankle alignment becomes is really a secondary outcome. So, measured resections are used to restore the joint line based in the thickness of the femoral component.

As Peter said, what you end up with is really an oblique joint line. But if you look at the mean hip-knee- ankle alignment, it’s actually very similar between kinematically-aligned knees and neutral mechanically aligned knees. The difference is that your joint line is more anatomic, or supposedly more anatomic, with slight obliquity.

You also end up with a mean internally rotated femoral component relative to the transepicondylar axis and I would argue that targeting the transepicondylar axis in every single patient may lead to a knee that does not recreate the normal flexion/extension axis of that knee. And 3D CT studies demonstrate that actual flexion/extension axis of the knee is actually slightly internally rotated relative to the transepicondylar axis in a large proportion of patients.

Looking at the clinical results, a prospective-randomized trial (Dossett, et al., BJJ, 2014) looked at mean hip-knee-ankle alignment—which was exactly the same between the kinematically aligned knees and the mechanically-aligned knees. The main difference was that the joint line was more oblique in the kinematically-aligned knees and at 2 years the mean Oxford, WOMAC, Knee Society, and flexion were all improved in the kinematically aligned cohort.

Most surgeons still aim for a neutral component and overall hip-knee-ankle alignment in knee replacement. I’m not going to argue that that is not unreasonable.

I do think, however, that questions remain regarding the optimal target for each individual patient. I think we need to question the norm in stating that just making everybody look the same is going to be okay.

I think the concepts of constitutional varus and kinematic alignment definitely have merit.

Moderator Thornhill: You both talked about the 15%-20% of dissatisfied or less than fully satisfied patients in a relatively pithy way. Tell me what is the source of this dissatisfaction and how we can make it better?

Dr. Sculco: Dissatisfaction, it’s multifactorial. Depression, anxiety, fibromyalgia, catastrophizing, and low preoperative Knee Society Scores. We all use that 20% as an explanation but if you look at the data, a lot things that cause the dissatisfaction are not related to the knee itself.

Dr. Nam: I think the number one reason is unmet expectations.

Moderator Thornhill: You’ll see patients who have total hips and they forget they had anything done; they’ll have a total knee and are still the same depressed, catastrophizing, melancholic person. Why does their knee hurt and their hip doesn’t?

Dr. Nam: I think a knee replacement is a more difficult surgery to perform. Setting patient expectations is critical. I would also say that this debate is great and it’s fun to argue and talk about alignment but we are looking at only 2D static images. When you have a patient’s dynamic constraints, muscle tone and gait analysis the story can be totally different. It’s really hard to say that patients are going to do well just based on their radiograph.

Moderator Thornhill: Okay Denis, George Santayana once said that those who forget about history are doomed to repeat it. The fact is that some of the kinematic alignment is like the alignment in the old PCA. Is that okay?

Dr. Nam: I think the PCA failed for a number of reasons; one of them was the patella-femoral complication. I think that when we look at these alignment targets we should be starting with boundaries and I don’t think anyone is going to stand up and say a 7-degree varus tibia is okay. I think that there are boundaries where maybe a 2-degree varus tibia is okay or 3-degree, or having a little bit of valgus at the distal femur. I think we should start with the kind of less severe deformities and see if that truly makes a difference because I honestly think those are the patients we have the most difficulty with. The severe valgus deformity or the severe varus deformity, if we can get them a stable, balanced knee, I think those patients tend to do okay.

Moderator Thornhill: Thank you, you guys have really helped us.

Please visit www.CCJR.com to register for the 2018 CCJR Winter Meeting, – December 12 – 15 in Orlando.

Senior Editor: Jay D. Mabrey, M.D., whose 35 year career in orthopedics included residency at Duke University Medical Center, service in the United States Army Medical Corps, Fellowship at the Hospital for Special Surgery and a long, distinguished career at Baylor University Medical Center where, in addition to his overall leadership at that institution, developed the Joint Wellness Program that helped patients get up after surgery more quickly, developed the first virtual reality surgical simulator for knee arthroscopy and chaired the FDA Orthopaedic Device Panel, is Orthopedics This Week’s newest contributing writer and editor.