“With 110 degrees of range of motion we can do most of what we do during the normal day, ” states Lowry Barnes. “There are major cultural differences that demand a knee that accommodates high flexion, ” avers Giles Scuderi.
This week’s Orthopaedic Crossfire® debate is “The High Flexion Knee: The Myth Continues.” For the proposition is C. Lowry Barnes, M.D. from the Arkansas Specialty Orthopaedics; against the proposition is Giles R. Scuderi, M.D. from Lenox Hill Hospital in New York. Moderating is William J. Maloney III, M.D. from Stanford University.
Dr. Barnes: “My title could easily be, ‘Implants never trump surgeon error or patient factors.’ With 110 degrees of range of motion (ROM) we can do most of what we do during the normal day. What do we know about high flexion versus conventional knees and patient perception? Studies have not consistently shown that there is any patient benefit with the high flexion knee design.”
“How often do patients use this high flexion position? Huddleston has shown that in our normal activities, only 0.1% of the time are we in a position where our knee is flexed greater than 20 degrees. If we look more specifically at outcome data comparing those patients who have the so-called conventional knee versus a high-flexion knee, two studies comparing these found no difference in either. What about gender-specific knees with high flexion or rotating platform with high flexion? Again, there has been no significant difference noted.”
“As for maximizing ROM, three variables affect that: patient, surgical technique, and implant design. Patient: we know that preop ROM has a certain bearing on postop ROM. And if you look at passive flexion in the OR following closure there would be a correlation there as well. So why do patients have decreased ROM? Obesity, for one…and stiffness from post-traumatic OA [osteoarthritis], or from prior surgery.”
“Then you have the psycho-social red flags: 12 cats, male over 50 whose mother answers questions for him, more than five body piercings…and the dreaded one: referral by an orthopedic surgeon who does as many total knees as you do. Then there are patient ‘medical’ factors such as those on chronic narcotics or pain pumps, etc.
“Turning to surgical technique we know that if we oversize the femoral component you can stuff your flexion gap, making it difficult to gain motion. If you over-resect the distal femur and are loose in extension, placing a thicker polyethylene to tighten the flexion gap makes it more difficult to get ROM. And there are technical errors, such as an anterior slope on the proximal tibia. And we know now from a number of studies that either internal rotation of the femoral component or tibial component can lead to abnormal mechanics and altered motion.”
“Failure to remove posterior osteophytes can lead to impingement posteriorly, as can not restoring posterior condylar offset affect ROM. And you can overstuff the patellofemoral joint by having a patellar construct that is too thick. We’ve done recent work both in cadavers and computer models, and found that there is a decreased ROM with each increasing 2/3mm of patellar thickness.”
“On the implant design side, we don’t want paradoxical motion. We don’t want the femur sliding forward in flexion. This might be treated any number of ways. It is less likely in posterior stabilized designs, medial pivot designs, and mobile bearings. Thicker posterior condyles allow for greater contact area in deep flexion. But it may be that because you’re taking more bone posteriorly it’s easier to clean out the posterior aspect of the knee. An anatomic trochlear groove relieves stress on the periarticular structures anteriorly. To allow flexion, make a deepened trochlear groove. The femoral dwell point—if moved back a couple of millimeters—can increase flexion by trying to prevent impingement posteriorly. Centered pegs may make a difference and anatomic tibial base plates may help get your tibial component in a more appropriate position.”
“So where are we going with this? If we have a high flexion knee are we going to have every other kind of knee as well (stable knee, correct size knee, etc.)? And how are we going to decide who gets which?”
Dr. Scuderi: “There are two recent presentations by Lowry, and he does achieve high flexion well over 135 degrees in all designs. What we need to ask is, ‘What is normal knee motion?’ and ‘Can we accommodate that?’ We know what the weight bearing range of motion is; we know about the differential rollback in the knees. And many times the preoperative motion dictates the postoperative motion.”
“High flexion involves knee designs that have gone beyond the traditional 125 degrees. But there are differences in patient-specific activities. In the West these are stair climbing and gardening; in the East these are kneeling, squatting, and cross-legged sitting.”
“What’s important is that patient perception of the outcome focuses on their ROM; they want the highest ROM possible. And I think that’s why manufacturers have focused on designing knees that would accommodate a high degree of flexion. Not give it to you if you don’t have it.”
“I believe in a posterior stabilized knee with controlled rollback, an improved contact area posteriorly, and less edge loading. There are numerous surgical factors affecting the situation. To get a better functional outcome the patient has to have a stable, strong knee, but we want to improve flexion with posterior condylar offset restoration, better rollback, and the rotation that one needs.”
“The literature contains many articles on a multitude of designs where patients have been able to achieve a high degree of flexion. Early results from some of these designs show that patient ROM has improved with good surgical technique and with approaching an average of 138 degrees. If we look at some implant designs, you can replicate high flexion in a healthy knee…and with that proper design you can get better rollback and improved kinematics of that knee joint.”
“There was always a concern about the stress on the patellofemoral joint; empirically we said it was not increased. In a study I did with Mohamed Mahfouz we looked at the patellofemoral forces at high flexion for the normal knee and compared it to high flexion knee designs. Again, the total knee experience is similar in patellofemoral forces in the normal knee, which actually drop off as one goes into high flexion. So high flexion isn’t a concern.”
“In a 2010 study by Tarabichi in a Middle Eastern population they achieved a high degree of flexion. That’s important because for the social, religious, and cultural needs of these patients they want a knee that bends to over 140 degrees.”
“A 2008 study we did with Argenson from France involved 500 patients and found higher ROM; Knee Society scores correlated with improved quality of life, more recreational activities, and better patient satisfaction. So Lowry, go visit the Sistine Chapel. God created Adam with a knee that went well beyond 125 degrees…and I think the expectation was that when he got his total knee, he got a high flex knee.”
Moderator Maloney: “Rebuttal?”
Dr. Barnes: “Thanks, Gil. Not only did you reference my articles, but you referenced a number of other articles that showed many of the implants that are not labeled high flex. We probably don’t need an implant that is part of a family of implants that’s not a high flexion knee and one that is because the challenge is who gets which knee, etc.
Dr. Scuderi: “I agree that it’s proper patient selection and good surgical technique. But you do want a knee that will at least accommodate a high degree of flexion because there are some issues on specific designs where you can get edge loading as those knees go well beyond 125 degrees…and that can result in some damage to the polyethylene. This is especially true if that femur has been translocated proximally you get a little lift off and have edge loading of the femoral component. I want an implant that will at least accommodate that high degree of flexion.”
Moderator Maloney: “Gil, I’m confused about how people use the term high flexion knee. Is it one that allows high flexion while maintaining some congruency or is it one that promotes high flexion?”
Dr. Scuderi: “It’s not the promotion of high flexion; it’s one that accommodates that flexion. It’s designed so that you have the contact area as that knee goes beyond the 125 degrees.”
Moderator Maloney: “So would you both agree that it’s the surgical technique and patient selection that has more to do with flexion than implant design?”
Dr. Scuderi: “Yes.”
Dr. Barnes: “Yes.”
Moderator Maloney: “What about the issue of patient satisfaction? Is that how we focus on knee flexion in terms of measuring it and warning the patient about being too stiff?”
Dr. Scuderi: “It’s not what we teach the patients. We need to be able to understand before surgery what their expectations are. For those that have excellent ROM preoperatively we must have them understand that our goal is to try to get that ROM back.”
Moderator Maloney: “Lowry, we all have those patients where we measure their ROM in the office and are patting ourselves on the back, but they feel stiff.”
Dr. Barnes: “That’s our real challenge. The question is, ‘Do they have kinematic mismatch or a rotational issue or instability?’ I’m not sure what gives that stiff feeling, but it’s something we’ve done.”
Moderator Maloney: “Gil?”
Dr. Scuderi: “Some of those patients, especially those we see in the first year, have good ROM like 125 degrees. There is some kinematic issue here; or they haven’t rehabbed the knee and it’s likely purely muscular. Most of those patients are describing stiffness and not pain. When we came up with a new Knee Society score and surveyed the patients, the pain level scores were low, but they were all stiff.”
Moderator Maloney: “Lowry, do you think some of those patients are those who had 140 degrees preop and ended up with 130 degrees afterwards?”
Dr. Barnes: “There may be some of that as well.”
Moderator Maloney: “Gil, what are the other concerns people have with impingement in posterior stabilized designs anteriorly, as well as increased radiolucency around the posterior femoral condyle?
Dr. Scuderi: “With radiolucency some talk about the loading and fixation of the implants. At least with my experiences these have all been cemented implants and I’m concerned about ROM in some of the cementless designs. My experience has been with cemented designs. When it comes to impingement it’s related to the kinematics and ROM. We talk about the impingement of the posterior stabilized spine-cam mechanism; I think that’s one of the advantages of a mobile bearing design because at least the spine-cam mechanism can move as a unit. However, when we compare those two studies from the Journal of Arthroplasty we found no difference in those groups as far as Knee Society scores and ROM, and no mechanical complications in a 2-4 year follow-up study.”
Moderator Maloney: “Thanks to both of our debaters.”
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