Louis E. DeFrate, PhD, Frank H. Bassett III, MD, Associate Professor of Orthopaedic Surgery, Biomedical Engineering, and Mechanical Engineering and Materials Science, Duke University talks about ACL injuries and working to educate people on how to possible prevent these kinds of injuries.
Interview conducted by Ivanhoe Broadcast News in October 2017.
Talk to us about ACL injuries, what is that, what does it mean and how common is it?
DeFrate: There are over four hundred thousand ACL tears in the U.S. each year it’s been estimated. ACL injuries happen in a noncontact mechanism about seventy percent of the time. That means you injure your knee without direct contact with another athlete. For example, an athlete sees a defender coming and tries to change directions and suffers an ACL injury. What our lab is really interested in is learning more about what causes this injury. Our goal is to use this to focus on prevention programs to better preventing ACL injuries from happening.
Unfortunately we’ve seen it with professional athletes and it just looks horrible. What happens when your ACL tears exactly and what have you been learning about why that’s happening?
DeFrate: It’s a controversial topic as to what causes ACL tear. Some of the studies think that the knee is buckling inwards, whereas some of the studies think it’s landing on a straight knee. There’s really a controversy as to what’s causing the injury. Our premise is that if we can better understand what’s causing the injury perhaps we can focus the prevention programs to improve their efficacy.
So what have you learned from that?
DeFrate: What we did was we looked at patients’ MRIs that had bone bruises on both their femur and tibia; on both sides, and we traced where the bones were and we traced where the bruises were. Then we used this data to create a 3D model of the knee and the location of the bruises on the femur and the tibia. Then we wrote some software, primarily written by one of my students Sophia Kim, that moved the knee around until these bruises overlapped. The computer used numerical optimization to find a unique solution to this problem, where the bruises overlapped the most. From this position we could predict what position the knee was in at the time of injury. In the predicted position of injury, the knee is very straight and the tibia has slid very far forwardI In the coronal plane, which means looking straight on, there’s not much of the buckling motion. What we think is happening is that the subjects are tearing their ACL when they’re landing on a straight knee and that a large buckling motion that you can see on videos of ACL tears happens after the injury has already occurred.
Why is that important?
DeFrate: So we think that learning more about what’s causing the ACL tears we can use in prevention programs to focus them better on what a dangerous knee position is.
I do want to mention it had always been believed that women were more prone but we’re not there yet right?
DeFrate: We did recently report some interesting findings on males and females at last year’s Orthopedic Research Society and the American Academy of Orthopedic Surgeons meeting. We found that there was no difference in the predicted position of injury between males and females. Although females may be more susceptible to injury, males and females are both tearing their ACLs in the same position.
So it may be the behavior leading up to the injury that’s causing this, that’s the difference?
DeFrate: Yes, our results suggest that men and women are both landing on a straight knee when they’re tearing their ACLs. We think avoiding that position might be the key to preventing ACL injuries from happening.
That’s important because that’s what you’re talking about when it comes to prevention and educating?
DeFrate: And that’s may be a challenge, to train people to land differently. But if we if we can better focus the programs instead of on a bunch of different mechanisms, on one particular motion, we may be more successful I think.
And that’s using the bended knee position; don’t land on a straight knee?
DeFrate: Right. Of course we need to do some more research to figure that out. One approach that we’re using is combining motion capture techniques together with our 3D MRI modeling and what’s called bi-planar-radiography, to reproduce the motion of the knee and calculate how much the ACL strains.
Explain that again, this is what we’re going to see your patient doing?
DeFrate: What we found is that when you’re jumping in the air, your knee is very straight right before you land. And then as you see the ground coming right before you land you have to begin to flex so you don’t have a hard landing. That’s when your ACL is stretched the most, right before you land. What we think is happening is that when someone injures their ACL, they land on a straight knee. They may not flex their knee in time to hit the ground. This results in an ACL tear and then the buckling motion that you see on videos of ACL injuries is happening after the injury has already occurred.
So this is all a way to help try to prevent people having the ACL injury?
DeFrate: Right, yeah. We have to learn what’s causing it in order to be able to prevent it.
And this would be the education and training to explain to people how to prevent?
DeFrate: Yes perhaps working certain muscle groups to help subjects to land on a more flexed knee to better prevent the injury from happening.
If you’re not an athlete are you still at risk for ACL injury?
DeFrate: Most frequently this type of injury happens in young people; the median age is roughly seventeen. It mostly happens in young active populations, but it can affect older athletes as well. It typically happens during cutting and jumping sports where you have to change direction quickly. Soccer and basketball are some sports that are high risk for ACL injury. So that will all be part of the training process to train people?
DeFrate: Yes, using this technology we could evaluate whether current training techniques can lower the strain on the ACL. We could ask someone to jump, measure how much their ACL is stretching, they could go through a training program, and then we could see whether it was effective in changing the way they land and how their ACL stretches.
If you already have the ACL tear that’s another part of what you all have been studying because it’s also the ACL reconstruction and how it’s done?
DeFrate: Whether you get your ACL reconstructed or not you have a very high risk of getting osteoarthritis. In terms of the osteoarthritis burden, ACL injury ages your knee thirty years. Osteoarthritis is a huge problem, it’s a leading cause of disability in the US, and it greatly limits mobility. Unfortunately there are no real good treatment options for osteoarthritis right now. So one of the things we’ve looked at recently is how the different surgical techniques can influence the placement of the graft. We found that it’s very important to get the ACL graft in the right spot. If the surgeon gets it in the wrong spot and you have a vertical graft you can have increased motion. Using our bi-plainer radiography we can image people doing various activities. We can use this technology to reproduce the motion of the knee. What we found was that depending on where the surgeon placed the graft, it made the knee move very differently. So if you get the graft in the correct anatomic spot it moved a lot like an uninjured knee. If you get the graft in the wrong spot it moved almost like an ACL deficient knee.
Talk about the ACL graft?
DeFrate: One of the important things we found was that depending on the technique used, there may be very large differences in where the ACL graft is placed. In one procedure, the graft was placed anatomically and is very diagonal. On the other hand, the other technique resulted in a graft that is oriented vertically. If the graft isn’t oriented anatomically, it may not have the appropriate restraining function. To investigate this further we built 3D models of the knee using MRIs and then asked people to do activity while being X-rayed from two perpendicular directions. From these images we could create 3D models of the knee flexing and the ACL stretchingWe used these models to compared how the knees moved when the graft was in the right spot and then when it was not in the right spot. We found very dramatic differences in the motion of the knee. If the graft was placed in the anatomic location it moved a lot like a healthy knee. If the graft was placed in the wrong location it moved almost like an ACL deficient knee;
And it was the one that was going straight up that is in the wrong position?
DeFrate: Right.
What was the percentage on how many might have been in the wrong place?
DeFrate: We don’t really know exactly. that’s a difficult thing to estimate. It’s been estimated a few years ago that somewhere around ninety percent of surgeons were using that particular technique. However, one of the strengths of this technology is we could show the surgeons exactly where they were hitting relative to the other knee. We could see where the ACL attached on the bone and we could tell the surgeon where they were putting it.
So this type of technology could be used in the operating room, in OR’s to show the doctors and surgeons how to get that in the right position?
DeFrate: Yes, in the future we can do that. How can people maybe hopefully prevent this from happening to them?
DeFrate: From a surgical point of view I think it’s really important to make sure you’re getting a graft in the right position. We’ve shown that, in addition to the differences in motion, that there is also dramatic cartilage thinning in the subjects that didn’t have the graft in the right spot. Ideally we’d like to prevent people from tearing their ACLs by learning more about what causes the injury and what we can do to prevent it and that would be ideal if people didn’t get them. We’re also working with some of the surgeons at Duke; Dr. Bill Garret is one of our big collaborators on ways we can make the surgery even better so it really mimics your healthy knee. How far off in the future do you think we will be seeing this kind of technology out there?
DeFrate: It probably will take a little while maybe five, ten years. Unfortunately this is a little tedious and time consuming, there’s a lot of analysis we have to do to make one of these. To make videos it takes hours and hours of analysis and hundreds of images.
Is there anything more you think that we need to say?
DeFrate: We also have been developing a new stress test of the knees, where we have subjects walk on a treadmill and image them using bi-planar radiography. We can use this technique to look at how cartlilage deforms and to see how your ACL is stretching while you’re walking. We can use this to evaluate the influence of surgical procedures or different interventions the health of the cartilage.
So that new stress test is that something that would be used then before the person has the injury or even after just to see?
DeFrate: Yes, we are starting out by evaluating high risk people, such as someone with an injury. And then maybe we can get an idea of what a healthy profile looks like. Then in the long-term we’d like to individually have people do this stress test of the knee and evaluate their cartilage function and health. Then maybe we can prescribe exercise or weight loss to improve how they’re loading their cartilage. Hopefully, we can use this information to prevent osteoarthritis in the long-term. Because we know that getting the right amount of mechanical loading is very important to maintaining cartilage health. As of this moment you’re not saying to people don’t exercise of course, you want them to exercise their knee?
DeFrate: Yes, exercise is one of the few things that we know is beneficial to your knee. But we don’t really know what the healthy optimal amount of exercise is. It may not be good to be running a marathon every single day without getting any rest. But we need more research in this area to better understand this problem
END OF INTERVIEW
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Louis E. DeFrate
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