Episode 12 | The Importance of Regaining Knee Extension After ACL Injury or Surgery

What’s up guys? Welcome back to the ACL Athlete Podcast. So today we’re talking about knee extension, why it’s important, why we should get it back, what are some of the parameters around it? So that’ll be the focus today. But before we get into it, I just wanted to say thank you to all of you. We just passed 1000 downloads, which is incredible.

I thought that my wife was probably just hitting play multiple times and just getting the count up, but it’s been really cool to see the support and everyone really just reaching out about this podcast and how it’s been helpful or sharing it with friends. So thank you all so much for listening.

Now to get into the episode for today for knee extension, this is something that gets missed a lot. So I see patients who come in all the time, and they might be four months out of surgery, they might be two years out of surgery, five years out of surgery, and they never got their range of motion. Now the bending is one piece that is the whole topic in and of itself, but in general, the umbrella of range of motion is important, and it’s one of the things that I talked about in the last episode of the Quiet Knee.

So it’s one of the four main components. But today we’re specifically talking about knee extension, which has much more implications in terms of getting your knee back to full function and ACL rehab and recovery, and that’s what I want to focus on today. So what is knee extension? So we primarily think of the knee being able to flex, which is bending the knee or extending, which is straightening the knee.

There is some rotation at your knee joint, but it’s very minimal. It’s still important, but the main thing that we’re always trying to get after, especially after an ACL injury, is getting the flexion and extension. So what I want you to do is take your leg and I want you to straighten out your leg. So you can imagine pushing the back of your knee towards the ground trying to tighten up your quad muscle or the thigh muscle that’s in the front.

And I want you to just kind of feel how that is. Now, if you have an ACL side, I want you to take that knee and I want you to straighten that one out. and try and feel how the quad feels there doesn’t feel even, and if it does, then great. If it does not, then where are you feeling it and just kind of think about where you’re at in the process.

This is all going to depend on the goal within the first two to three weeks after an ACL injury, and especially after a surgery, we are trying to get this knee extension back to the uninjured side. So you might be wondering why is the extension so freaking important?

I’ll tell you why. So number one, that it can be linked to osteoarthritis. They have done studies where they have looked at loss of knee extension and range of motion at the knee joint after an ACL reconstruction which can lead to an increased risk of osteoarthritis. So a lot of times what I will see is that patients will come to me after they’ve been doing therapy somewhere.

And their physical therapist or trainer or whoever it is, says it’s okay to get to zero degrees of knee extension. That’s pretty much a straight line at your knee joint. And if you look at the normal presentation of a knee, typically, there’s some hyper-extension where it kind of goes back a little bit by three to five degrees, and the research norms shows this, but what happens is, is that it can sometimes take too long, or maybe there’s a rush to get to the next phase of more of the fun stuff, if you will.

It can get left behind, but that is a huge foundational piece and they’ve seen that link to knee OA, even as little as deficits from the one side to the other of three to five degrees. And it’s even worse if you go above five degrees.

Next is joint mechanics. So the way that the joints interact with each other, we call that arthrokinematics in the PT world.Your tibiofemoral joint is where your shin bone and your thighbone connect to each other. There can be mechanics that are messed up with that. Also, your patellofemoral joints, or where your kneecap interacts with your femur, which is your thigh bone. So this is all like more PT jargon, but these are things that are important because as you can imagine, if the normal structure is not restored, then stress starts going to other places within the knee because it can’t access that range of motion. And this is something to just kind of caution as you move forward. Because if you’re going with higher intensity exercises, it could lead to increased stress in other areas such as your kneecap or your patellofemoral joint where people can get pain a lot of the time.

So this is something just to consider as you’re moving forward. This can also place increased wear and tear towards your articular cartilage, which is the tissue that is in between these different joints that can absorb load to transfer force and create cushion to reduce friction around these joints.

Now don’t go freaking out. This is just something to be aware of, and I think in clinical use, people will hear this all the time where their cartilage is completely gone, or it’s bone on bone. Don’t worry about all that. It’s just something more to kind of keep in the front of your mind and in the importance of working on your knee extension.

Next up is your screw home mechanism. So this is something that is very technical, but I think it’s very important and can get missed. It goes back to how the joints move together. When you go to straighten your knee, there is a slight rotation depending on the position at that knee joint, and we call that the screw home mechanism.

And this can be something that can get missed a lot as well. So if you can restore the normal joint mechanics, then the screw home mechanism, it can allow you to get into that end range knee extension. We call that terminal knee extension and to be able to activate your quad and access that range. 

All right, so now on to a little bit more of a practical sense, if you will. So, the quadriceps activation itself is best whenever we’re at full terminal knee extension, and that’s gonna allow us to also fulfill maximal strength within the quadriceps as well. So imagine this, you’re gonna take your elbow and I want you to straighten it out. Like you’re gonna extend that elbow, straighten it out, feel the back of your tricep, feel how hard it is, and then now what I want you to do is bend your elbow just slightly and then try to engage it again.

So don’t straighten it out. Just keep it slightly bent. Which one feels more contracted and activated? And it’s the one with the arm straight and you can almost think that your elbow has a very similar function as your knee. They work the same; they have a hinge. There’s a little bit of a rotation, more of a rotational component outta your elbow.

But the main thing that I want you to know here is that your quadriceps works very similarly to your triceps. And if you don’t have that end range for your tricep and your elbow, then you’re not gonna be able to access that full contraction. Same thing as your knee, which is very important. So you can use this as another practical example of let’s say you’re doing a pushup and you.

Just hang out in that straight plank position, and you have to have that just bent elbow the entire time. One, your tricep is gonna get very fatigued because it’s gonna be constantly on all the time, anytime you’re in that position. That’s why we can hang out in plank positions more when the elbows are straight versus bent.

So same thing with our knees here. I want you to think about, if you can’t get that normal knee extension, then any time that you are walking or up on your feet, your quad and your hamstrings are gonna be on most of the time. So they’re not gonna really get much of a chance to relax, and this also leads to just a funky gait.

So you got this really weird walk going where it’s almost like a little bit of a hobble, or you might swing your foot around, which is very common with people who don’t get their knee extension back and then it alters your gate mechanics as well. So these are the reasons why knee extension is important and this isn’t exhaustive, but these are some of the most important pieces that go into this.

Now, let’s talk about the reasons why it might be hard to get that knee extension. I just talked to you about the importance of it. I want you to understand maybe some of the reasoning behind it. Now all of this to say this is purely educational. I don’t want you to be making your own diagnosis. This is something where having a physical therapist or you know, a medical professional to help you along with this is very important.

But I do wanna discuss some of the potential reasons behind this. So let’s get into it. Number one is, Whenever you have an injury or whenever you have surgery, there is pain associated, and so that pain can be restricting your ability to get your knee straight. There has been trauma to the knee, whether that is drilling holes or putting a graft in or just tearing the ACL itself, it is trauma to the knee, so pain will be associated and that might be one of the reasons why it’s hard to get that knee extension. Swelling might be another reason why the joint itself has a lot of fluid or effusion in it. So this can really impact the way that the joints interact with each other, but then also it is just really swollen, so it could be difficult for those joints to approximate or to get into that terminal knee extension as they need to.

So swelling is definitely a huge culprit and anyone who has had this injury is very familiar with swelling and it is the bane of all PTs existence and people with ACLs because it can come and go. It’ll show up whenever it wants, and sometimes without even any reason at all. But especially early in this process, you will see swelling.

So that’s one of the things that contributes to quad inhibition. You will hear the term arthrogenic muscle inhibition–that is a term that can be used where the quad itself will not activate as well. And there are many different theories behind it, and we’re not gonna dive into those specifically, but it can be very difficult to turn on the quad, whether it’s from the surgery itself, whether from the brain, or from a certain nerve type blocks that are used, which is the next point…

The nerve blocks that they use are to help to desensitize so they’ll use an adductor one, which is part of like the groin area and then your femoral nerve. When I got mine, I got femoral nerve blocks in both of mine. And so that can impact the motor function or the ability to contract your quad muscle.

That is just another thing to consider. And then there are cyclops lesions. So this one can get missed a lot and it’s in a smaller percentage but we don’t know exactly where a cyclops lesion comes from. Sometimes we think it can come from the old stump of the ACL that might not have been cut out, or it could be from potentially some of the tunnel drilling that happens.

And what it is, is almost like the scar tissue that sets up and it can impact the way that the knee can extend and flex. What people will see a lot of times is anterior knee pain and an inability to make any progress in their knee extension. We’ll have to do an episode completely on that but a cyclops lesion is just something to be aware of. 

Fear is one of these that I think can get missed. Just the thought of trying to contract something and maybe thinking something’s going to tear. They took a tendon from your patella tendon or maybe quad tendon and you’re worried if you try to straighten your leg, something might happen. Right. And I remember when I had my ACL surgery, I was a little worried, like if something was gonna kind of go wrong, whether the graft would come out or I did something to my hamstring or my quad…

So it’s, it’s fair to feel that, but just be sure and know that you’re okay with this and that the fear is normal and that the pain and the swelling, all those things are going to limit you just because of the way this process is.

And one last thing that I think is important to note here is a potential bone bruise. So when you have your ACL injury, maybe there was a bone bruise in there and it’s something that might be necessary to delay surgery because with a bone bruise, there’s gonna be more healing that is needed. You’ll see more pain and inflammation and swelling. So it’s just something to note with this process. Maybe surgery needs to be delayed because it can really influence how the joint is moving, getting that extension and flexion back, getting your quad going, and if you put it off, then maybe you might have less complications when you actually do have the surgery if you choose to do so.

And that would be something just to consider. Not everyone gets a bone bruise, but it does happen depending on the way that the ACL is injured. So just think about that as you’re thinking about your knee extension and maybe there’s a lot of joint swelling and pain. 

The other areas to look at with this is what is your kneecap or your patella like? How is it moving? The mobility of it? How is your femur and your tibia? That is your shin bone in your thigh bone. How are those two interacting with each other? Soft tissue restrictions… So we have our hamstrings and our calves at the back of the knee along with other muscles, and then you have your quads.

So all of this soft tissue is all surrounding the joint. And that is something important to know because maybe there’s a contracture at your hamstrings, maybe there’s something where it’s really tightened up to where it’s really limiting that last few degrees of extension. So something else to consider.

And then thinking about where the graft side is. So if you have a patella tendon graft, then maybe it’s restricting that kneecap to be able to move because there’s some scar tissue or maybe the patella mobility is not very good. So these are things that are important but I do not want you to go off and stress about 2000 different things that might be going on. I know that this can be a lot of information, but I just wanted to be informative to be able to know, okay, there are different components of why it is so important to get your knee extension back, and also maybe some contributing reasons as to why it’s happening that doesn’t get explored enough.

And this is where I think it is important to work with someone who knows about this, who knows about this injury, who knows about the knee, who knows how to be able to assess for some of these things. And one of the things that I wanna make sure I leave you with is learning– okay –what is it that I need to get back to?

One is if your other knee is uninjured, that is gonna be your baseline. You want to get it to the same as the uninjured side. That is the baseline of knee extension that we’re looking for. And if that side has been injured, then you want to try and just make sure that you can maximize as much knee extension, which for most people, typically it’s around five degrees of hyperextension so going right past zero. And then working towards being able to contract your quad really well. So these are all things that are important. 

This podcast episode is not necessarily focused on just different techniques and things like that because this is also just going to vary so much from individual to individual, which is why I think is very important to have a coach or a physical therapist, someone that you trust with this to make sure that you can get there and get the results that you want. So make sure that you are focusing on the extension as early as possible, get the range back within the first two to three weeks, and if not, keep working on it. Make sure that you can tackle these different reasons and make sure that you keep at the forefront why it is important to get this back and not rush too quickly into the next phase of your acl.

Cool. Awesome. Well that’s it for today, guys. I know this was a lot on knee extension, 20 whole minutes on knee extension. You are welcome. Appreciate you guys as always, and thank you so much for listening. This is your host, Ravi Patel, signing off.