Episode 251 | Knee Flexion Truths in ACL Rehab: What’s Normal, What’s Not, and What Actually Matters

What is up team? And welcome back to another episode on the ACL Athlete Podcast. Today, I am keeping it super short and sweet, and I want to talk about one thing in particular: knee flexion. This is where you bend your knee or bring your heel towards your butt. One of the common goals, along with extension, when you’re post-injury and post-op ACL. 

When we are early on, we are trying to restore both knee extension and knee flexion. I’ve done an episode on this before, which one should you prioritize post-ACL surgery? If you have not caught that, that’s episode 190, where we talk about which one you should prioritize. 

Now, I’m just going to give you the brief cliff notes here because it’s going to help me lead into the flexion conversation here. We are trying to prioritize extension first. We want to make sure that we can get that heel pop. Making sure the best test is to look at, when you sit down on a floor and you have both legs extended out. You’re on a hardwood floor, you do a quad set where you activate that quad, and usually on the uninvolved side, that heel will raise up, even if it’s just a little bit. We call that the heel pop test. And then on the involved side, we want to get that matching. That is basically a proxy, a test. If you can get that to match your uninvolved side, then you’re in a good spot for extension. We want to prioritize that as number one post-op.

Now, what happens is that people will often work on flexion more. There’s not as many degrees to work on with extension. It also depends on how much your physical therapist, your surgeon might prioritize extension or really encourage you to get that. We see a lot of times people are aiming to get to zero. When, in reality, we need to match hyperextension of what the uninvolved side is. Only caveat is if you have excessive hyperextension, we’re talking about minus 15 degrees of hyperextension, which is not the majority of you, it’s 5% of people, if that. With that said, like most people need to get beyond zero to get terminal knee extension, that heel pop that we are looking for. 

Now, the focus here is on flexion, and the reason I’m bringing this up is because a lot of times people will be like I’m not at a certain point with flexion. I will say that this will vary across the board for people. Now, for us at the ACL Athlete, we are aiming for within the first two weeks. And let’s assume there’s no restrictions like a meniscus repair. Even if you have a meniscus repair, usually that can be limited to maybe 90 degrees of flexion in the first two to four weeks, for example. It can vary across the different repairs, and protocols, and surgeons’ restrictions. But with that said, let’s just talk about without any type of other additional repairs, you’re talking about ACL only. We are going to aim to try and get to knee flexion within two weeks. We’re going to try and get there at 90 degrees. That would be an ideal time point for us to say like, “All right, if we can get to 90, we’re in a good spot at that point.” And then within four weeks, we’re looking to try and get towards 120 degrees so that’s really our focus there. And then of course, we have ranges depending on the repairs. As I had shared, even if you have a repair and you have 90 degrees from the get-go, as like the way the restriction that you have, we still try to get there within two weeks, and then we try to maintain that until we get more freedom to be able to get more flexion based on the restrictions.

Now, a lot of times, what people do is that they will focus a ton on flexion and will ignore extension or be like, “Ah, it’s fine. It’s straight. When in reality, we need to make sure we are prioritizing that extension. But the other piece here is I want to talk about is that when people get to 120, usually we’re in a good spot. So that’s usually our threshold where we’re like, “Okay, you’ll get the rest of the way there.” Now, that doesn’t necessarily mean we let off the gas on working on flexion. But for those of you listening, if you are three months out, if you’re four months out, and you don’t have full end range flexion. And our test for this is essentially doing a tall kneeling rock back. What you do is you’re on both knees on the ground and you’re going to hit your butt back towards your heels and you’re going to assess and see, “Okay, what does that feel side to side?” It’s like a yoga pose that you can see, like people are on their yoga mats and then they just sit back with their shins against the ground and their butts all the way back towards their heels; natural sitting position for a lot of people. But this is something that we use as an assessment. What you’ll notice is that when you go to do that on the ACL involved side, if it’s not fully restored yet, you’ll feel a little bit of tightness. You may feel a little bit of discomfort in the backside of the knee or maybe in the front. It just feels like a balloon, just because there might be some fluid still in there. This will vary person to person. 

With that said, we are going to use this as our assessment to help us know, okay, does this person have this fully restored comfortably? We want to get that back, especially if it’s sport-based, activity-based, but from a natural human access to positions, we want full extension, we want you to get back full flexion. It’s crazy the amount of people that we get who are months and years out who never get it restored, or they get it like 70% to 80% there. Range of motion is one of those things that is harder to get back, the further and further out you are from your injury and from your surgery. It’s the tissues naturally just come to a certain point where it don’t want to go as much, and it get set in its own particular stiffness, if you will, all the fibers and the different tissues within the knee. So that’s why we need to maximize this as much as possible within that first early post-op period. But then throughout the process, if it has not been fully restored yet.

When you rock back on your heels, you’ll feel that tightness. You may feel some discomfort in the back of the knees. I like to have people to hold onto something in front of them, or they could do like a quaded rock back where their hands are on the ground and rock back slowly. But the tall kneeling rock back is our ultimate test and proxy, just like the heel pop test. What we normally see is that on the uninvolved side, you’ll come back and you’ll put more of your weight on that side as you rock back. And then you’ll lose a little bit of weight on the involved side. And that’s because we don’t have it fully restored yet. But the main point I want to get across here is that we want to work on this over time, and it’s not just one full hour session of working on knee flexion. Range of motion work is chipping away just like you’re trying to chop out a tree with an axe. It’s not going to be one big chop; it’s going to be chops over periods of time, and it’s the same thing here. The way that we say this is, instead of one big hour-long session, you focus on this, I’d rather you spread this out across the day. Do it three to five times, even get a few sets in if you can. And that’s going to be helpful to just slowly microdose some of that work in. But you’re going to have to chip away at it consistently day over day. 

Now, we will have breaks with that with our athletes, of course, maybe there’s a strength training day with a little less range of motion work, if you will. They’re working on range of motion through their strength work, but then we might have the mobility work be a little less in volume on that day. And then there may be rest or recovery days where they’re focusing a little bit heavier on range of motion work. But, it’s not going to be once or twice a week, and you expect to move the needle with mobility, especially for a knee extension or flexion. It’s going to be chipping away at it consistently, five, six days a week, to be able to make sure you move the needle with that. 

I think that’s super important to share with you guys and also to know that everyone kind of ranges in terms of restoration of this. While we aim for the two-week mark for 90 and four four-week mark for 120, not everyone hits that perfectly. The thing is that we are aiming towards 120. And then once you get past 120, I will say that if you continue to just work on it, be consistent, it will come. Everyone that we work with, to be honest, once we hit that point and once we continue to chip away at it, they end up getting there. It might take some people, maybe four, six weeks. And there are some people who just get there and it’s magical. There’s some people who take nine months. And it is one of those things that I wish there were like very clear cut, this is exactly why, but in reality, everyone’s on their own journey. There are so many contextual factors between life and all the other things they’re dealing with. The surgery itself, the injury itself, all kinds of other personal factors are going on. The rehab they’re doing. There are a lot of layers to this. I think it’s important to share with you guys, let’s prioritize extension. But for flexion, once you get past 120, keep working on it. But don’t feel like you need to spend all the time in the world working on it and keep chipping away, especially at making sure your extension restores properly. Making sure your quads are active and working, making sure your swelling goes down, especially that’s the biggest one I see people have breaks in their process because they’re just constantly dealing with even low levels of swelling. And then making sure that strength is progressing appropriately. Those are the pieces that we need to bucket and work on through this process. 

Therefore, you can work on that flexion, work on the extension, prioritize extension, but then also with flexion, get it to those certain points, and then layer that stuff in and chip away at it, even as you get into the later parts of the process. If you do this properly over the course of months and months, then you’ll be able to get to that knee flexion. It can have some variability in those end ranges. I would say the last 10%, 20% sitting back fully on your heels takes a little bit more time, so keep chipping away at it. We’ve had people who join us, at six months or eight months, or even years out, they just never did intentional work on it, and then eventually they layered that in. Within four weeks, six weeks, they get there. Some people take longer, some people take shorter. It’s just all about making sure you have the right prescription, making sure there’s objective testing with it, and then being able to assess and adopt the program as you go. 

I hope this is helpful. Less than 10 minutes was my goal. I hope that we hit it, maybe, but we will see. All right, team. Until next time, this is your host, Ravi Patel, signing off.