Episode 297 | Audit Your Knee Extension: A Simple Assessment for ACL Rehab

What is up team and welcome back to another episode on the ACL Athlete Podcast. Let me start with something that we see quite often. An athlete comes to us, and they’ve been told that their knee extension is fine, that maybe it’ll come back with time, or to just keep working on it, especially if they’re in those early windows, let’s say less than three months post-op. They’re told to keep working on it; it’ll come back with time, or maybe it’s normal, especially if someone has achieved just a zero-degree extension.

In particular, I’m thinking about one case that has come up recently where they were much further out. They had a scan earlier on because the knee wasn’t acting right, and we’re talking about the early months of post-op. There was something that came up on there, but it was essentially considered normal. Then they started to feel like they were the crazy ones as time went on, and the knee just wasn’t feeling normal. They weren’t getting the extension back, or it was just feeling grumpy all the time, and it wasn’t really progressing like they were hoping, especially from a range-of-motion standpoint.

Nobody was necessarily finding out this issue. So this person comes to us, shares these findings, and then we assess and see certain things. We put some things in place to determine: is this more that they aren’t doing the right things, or is this more of a biological thing? That’s one of the things we’re really trying to determine, especially for someone who’s coming in later in the process, where they’ve been doing some rehab but are dealing with issues. Is this more of the body’s internal biology having an issue that we’re up against, or is it truly that they just weren’t given the right rehab approach to progress things forward?

We’re looking at this and assessing, and when we look closer, there’s something in the joint that was getting in the way this whole time. I want to be really clear here that this is not about blaming anyone, but this is what to look for because it gets missed a lot. I think in this episode, the goal is to be able to audit your own knee extension, what the results mean, and what to do next.

It is one of the most common issues in ACL rehab that comes up early, and I would say the majority of the time, it is something where the can gets kicked down the road. Don’t get me wrong, there are situations where we need to just give it some time, and some knees are tricky. But this comes back to pattern recognition and working with someone who knows this process, so there can be objective metrics connected to it. You also need to be able to have this tracked within weeks to see how the knee is progressing and whether there is any positive shift.

Especially if you’re doing all the things you can control, you’ve dialed things in, and things are not improving, then this is something that needs to be looked at further. Because of just the way that the procedure goes, when you’re in those first three or four months, you might have a follow-up visit at month three with your surgeon. Again, they’re typically looking at you and evaluating you in those moments for maybe five or 10 minutes max. They’re looking at the knee; it’s more of a conversation, very brief, and then you carry on: keep rehabbing, right? Or it’ll come with time. Unless there’s a very big red flag apparent, it’s typically, “Let’s just keep working on it.” 

Again, these problems don’t necessarily always arise immediately post-op. They could also develop at month six, month nine, or later in the process. But it’s important to make sure that this is always being audited, always being tested to make sure that it is there, it is maintained, and it is never lost. That is one of the things that is really clear here. 

What was so sad about this situation is that it could have been caught very early, and this person could have had a much different trajectory than being 15 months post-op and having the same issue still there that could have been caught earlier on imaging. 

Today, the goal is to talk through extension in a little bit more detail and an auditing process of yourself, so that any of you who are dealing with extension are able to look at this yourself, maybe talk with your PT, talk with your surgeon, and recognize some of these patterns. You can determine whether you’re in the category of “keep working on it, maybe,” or whether you’re someone who needs to look into it a little bit further. What’s the next step, just to be prepared, versus waiting another three months and still being stuck in the same place?

This is something, again, like I’ve shared in previous episodes: I get that we have a biased selection of people who are having complications in cases because they’re not getting the help that they need. We’re probably seeing more of the harder cases. Yeah, we might see more cyclops lesions, more scar tissue, and things like that. But I think what is referenced in the literature, or what is also mentioned in surgeons’ offices, is not really representing the whole. There’s way more of this stuff that is happening as a secondary byproduct of this ACL surgical process. The important thing is to be in front of it, so that you can get the help that you need. If there needs to be another clean-out procedure, that is done versus getting a year into this when it could’ve been addressed at month four.

If you are post-injury, post-op, I would argue knee extension is the number one priority in this process. It’s high up for us. It’s a part of the quiet knee, but it supersedes knee flexion and coincides with getting your quads active. It’s going to be the number one priority for us, and here’s why.

The further out you get from this injury, or especially from the surgery, the more that the joint settles into where it wants to be. It’s much easier to get that extension back because when you have the surgery, the surgeon goes through cycles of flexion and extension, checking to make sure you have full terminal knee extension. They’re also making sure that you have full flexion. So that joint has access to that as you get out of surgery.

Of course, then there’s swelling, the inflammatory process that takes place, muscle guarding, and some of those things can inhibit being able to access that immediately. That is something that we have, but the further away we get from surgery, the more these fibers start to heal, and everything around the joint starts to create its new normal.

If someone were to go six months with 10 degrees of flexion, or extension, if you will, they’re going to start to normalize into that, and it’s going to be way harder for that person to get back to zero or hyperextension versus the person who is in the earlier weeks of their post-op period. The joint is not fully settled down yet and healed, and the tissue is going to continue to adapt to whatever positions you leave it in. We want to restore that as early as possible.

And I’m going to say this one twice because it really does matter: knee extension does not get better with time. It does not get better with time. You have to intentionally work on it. Otherwise, it keeps that slight bend, and you can just settle in there. It might just be a slight bit of flexion as you walk or a slight little bend.

Those of you who have a little bit of knee extension that is not fully there, you know what I’m talking about. We have athletes who are very familiar with this, and we are helping to work through these things as they come in. It’s something that I think is really important to understand: a slightly bent knee is not okay, and also, in our opinion, zero is not okay unless that is your norm on your uninvolved side.

In our experience, when you don’t get that knee extension back, and also in the research, there’s a trickle-down effect. More scar tissue can build into the knee. That could be around the joint, and it could also form as a cyclops lesion. We have data to support that if we don’t regain extension, cyclops lesions are more likely. It can turn into a limp that inevitably will transfer over because you don’t have extension, and you need extension to be able to go through a gait cycle. It will impact the way your quad will fire and the way that it should. If you try to extend or straighten out your elbow, you have hyperextension in your elbow. If you can only get to zero, you’re actually going to be shy of being able to fully activate that tricep just like you want to. The quad works the exact same way.

The other thing that’s so important here is that osteoarthritis is also connected to not regaining extension. Shelburne has done some studies on this, and the thing is that it changes the way that the joint interacts with the patella, the femur, and just all of the mechanics of the joint and where stress is being put when you go through a gait cycle, when you jump, when you do all kinds of things that load the knee.

If you don’t have full knee extension, that is going to impact where load is being placed on the cartilage and all around the knee joint. That is just a general domino effect that can happen when extension is not fully restored. This is something that I have talked about in earlier episodes, so go back to listen to those. I’ve done deep dives on knee extension. A lot of people hear one of two things, which is very common. They’ll either hear it from their physical therapist or their surgeon, and they’ll say, “Oh, zero is fine. We intentionally did not want you to get into hyperextension.” 

Then they’ll also hear maybe that they spend two to four weeks working on it, or maybe a little bit more time, and then they move forward because the protocol or the timeline just says it’s time, right? You’ve been working on the quad sets, straight-leg raises, which are things that are typical in most initial post-op stuff that people do. But with that said, over time, it’s just, we move on to other things. Good enough does not work in extension. It does not. Good enough is—what’s the saying? Good enough only works in horseshoes and hand grenades, right? This is something that it doesn’t work.

We need exactly what we need here because there is a foundational effect from this. You want to build this in, and then there’s a domino effect of what that impacts from a re-injury standpoint, a performance standpoint, and all the other things that I had shared earlier about what this could lead to.

Zero is not the goal. I don’t care who you talk to. Zero is not what normative values are. If you look at most people’s knees, they hyperextend. It could be minus two, it could be minus five, it could be minus seven, it could be minus 10. For the hypermobile people who have excessive extension, they could get into minus 15, minus 20. We’ve seen it. The thing is, it’s more rare. Most people are not dealing with excessive hyperextension. Your gold standard is your uninvolved side. Again, with the caveat of hyperextension in people with hypermobility, minus 15 or minus 20. But for 90% of cases, most of you are not going to have to really deal with that, and the uninvolved side is going to be your gold standard in what you compare to. You’re not comparing yourself to some averages or whoever else is in the clinic, Bertha or Ronald, whoever it might be. You’re matching it to your own other knee.

If you have also had an injury on that side, and let’s say extension was not regained, then we’re going to try and get you into some hyperextension. That is also going to be looked at in terms of making sure functionally you’re not limited and you’re able to do all the things you need to, from quad activation, walking, and all the other progressions from there, to make sure you have back what you need.

With the hypermobile athletes, I’ve talked about this before, but we might be only getting back minus five or minus 10 of that hypermobility or the extension versus that full 15 or 20 degrees of hyperextension. That’s something where there is a certain threshold, but again, it doesn’t apply to most people.

The one thing that I want to bring into this is that I was digging into my textbook, and I was also doing a further literature review of what normative values are in the knee extension world. This is the thing that I was like, I remember it being in hyperextension and being in the five to tens.

I’m going to read this to you directly from my functional anatomy book, Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation, Donald Neumann. It’s an awesome book, a very foundational book in the process of understanding joint anatomy, functional anatomy, biomechanics, and all the things. I geeked out on this book.

All right, here’s what it says, and I’m reading this as I’m holding it in front of me: “Knee flexion and extension. Flexion and extension at the knee occur about a medial-lateral axis of rotation. Range of motion varies with age and gender, but in general, the healthy knee moves from 130 to 150 degrees of flexion to about five to 10 degrees beyond zero degree in the straight position.”

Meaning it can go from minus 10 to minus five, and it can also go from 130 to 150 degrees of flexion. That is something that is coming straight from this textbook. When you look across the research and when you look across normative values and resources that we use, it typically says, yes, there’s zero included, but then five to 10 degrees of hyperextension is normal. Those are within normal limits.

I’ve tested enough knees at this point that I promise you the majority of knees go into the negatives. Any orthopedic surgeon you talk to who tests knees truly there is some negative degrees. When you let line up 100 PTs and see what they say. I promise you that when you assess extension, there is going to be some hyperextension for the majority of the people we are assessing.

This is really important because zero is something that we have to see all the time, where people are like, “My PT said zero is fine,” or, “My surgeon said zero is fine. We don’t want you in hyperextension.” I disagree. That is the thing that we need to get back because it is important to the architecture of the joint and the way that all these dominoes really do influence the way that the knee is going to respond to stress, force, and load. We need to get that back.

What I want to talk about next that’s really important here is just how we’re going to assess this. I’ve talked about this before, auditing your flexion and extension, but today we’re focused on extension. This is the easiest self-audit there is, and it’s how we assess extension remotely. People ask me all the time, even with remote, like, how are we able to see this?

Technology is awesome. We’re able to really pull so much from the remote side and get so much detail. This is something with hundreds and hundreds of ACLers at this point: we’ve never touched their knees, and we’ve been able to assess their range of motion, implement strategies to regain their range of motion, and assess appropriately.

Here’s the setup for us to be able to look at their terminal extension side to side and see how it works and what it looks like. You have a hardwood floor or a hard surface. We do not want to be on carpet, not on a bed. We want something that is hard. You’re going to be barefoot, no socks, nothing underneath your knees. Your legs are going to be straight out, and you’re going to be sitting on your butt on the floor, with your hands right next to you. You could also be lying down as well, but you could easily just sit on your butt and have your feet straight out in front of you.

Step one is we’re going to look at the active test, which is really just going to be a quad set. The detail here is important because a lot of times people will do this, and they’ll just push into the ground, and it’s actually activating their hamstrings. Maybe some quads are getting active, but we need to make sure we do this correctly.

When you start on the uninvolved side, you are going to do a quad set. The goal is to squeeze your quad, and what should happen is the gap underneath your knee is flattening down towards the ground and the floor, and your heel lifts up off the ground. You’ll feel it getting lighter. Both the heel and the back of the knee should not be in contact.

The back of the heel should be lifting as you flatten the knee down to the ground, and your heel lifts up off the ground. That is the heel pop. We want that heel to pop up off the ground. It might be the ability to slip some paper underneath the heel. It might be a half inch or a very thin book, or if you’re hypermobile, you might get some height there. You might get an inch or two or more if you’re super hypermobile and you can get that heel pop going. Everyone is different, but note it on your uninvolved side. This is your standard here in terms of what we are aiming for.  Now do the same thing on the involved side. Does your knee flatten to the ground? Does your heel lift? Can you see and feel your quad contract?

Step two is the passive test. This one you’re going to need a rigid strap, a belt, or a towel, not a stretchy resistance band. Do not do your knee extension work with a stretchy resistance band. Do something that is rigid. Hook it around your foot and use your hand to hold the top of your thigh just above your kneecap down to the floor. You’re going to kind of overpressure down. The goal is to keep the back of the knee flat and pull the heel up with the strap using your arm, and you’re not activating your quad whatsoever. The passive test is no muscle activation. The active test is you’re using your quads to get into knee extension. The whole leg should not lift up with either of these tests. You’re flattening the back of the knee down into the floor and seeing how far the heel comes up with the quad relaxed, and this is the passive test.

Now, you’re going to do it on your uninvolved side first, and then do it on your involved side. Now you have data. You have assessed passive on both sides. You have assessed active on both sides. You also need to know how it feels on each side. Is there some sharpness, anything dull or achy, something around the kneecap, something in the shin? That all matters too.

Write it down as you do these four different ones. You’re doing the active on the uninvolved, the passive on the uninvolved, and then the active on the involved and the passive on the involved. Four different quick assessments. I would suggest recording a video. You could do it from the side. You could also do it from the bottom, where you can see the bottom of your feet to assess the heel height side to side.

Now you have that data along with some notes with it. Here’s how you read the results. The key rules: if you can’t get there passively, you cannot get there actively. Passive is the door you have to go through first. Think about your shoulder. If someone lifts your arm for you, again, you’re not doing it, with your muscles relaxed, and it gets stuck at, let’s say, parallel to the ground. If they lift it just to your arm out in front of you, parallel to the ground, no amount of strengthening is going to get that arm overhead. The joint won’t let you get there, so you have to get that passive range first before the active allows you to get there. That is just a very basic principle of physical therapy and joint mechanics.

Here are your possible outcomes when you look at this.

Outcome number one: passive matches the other side, active does not.

This is actually good news, so we love to see this with our athletes. It means the joint has access to the position. You can get there, and now it’s more of an active quad-related thing. There could be some symptoms that are impacting that too from activating, but we’re working a lot on that terminal extension through activation and some techniques, quad sets with some assistance that we have, using NMES or with a strap and different movements, and getting that muscle to recreate the position. We can work with this.

Outcome number two: passive and active both fall short.

This is where we have to play detective. Is it muscle guarding? Is there swelling in the joint that’s limiting it? Is there something structural biologically, like cyclops lesions or other scar tissue? This one needs a closer look, and it could take techniques to open up the passive. Again, it doesn’t mean it’s automatically scar tissue, but it is something where we need to put certain techniques into place to get this thing to open up based on what we’re seeing. If it doesn’t, we may need some imaging, but you need someone experienced to be able to assess this very clearly.

Outcome number three: both match the uninvolved side.

Great. Now we check it functionally. What about standing? How does it look with doing terminal-knee-extension-based movements? What about walking? How does the knee go through extension through a gait cycle? What about other positions that need terminal knee extension, like an acceleration-based position?

We’re looking at extension as an entire profile. It’s not just what does it look like on the ground or on a table. It’s also looking at it through a bunch of different positions to build an overall profile, not just one single number or position.

But you do have to have isolated extension all by itself in order for it to be accessible in those other functional positions. No one has terminal knee extension in standing, and then when you put them down and lay them down on a table and assess them passively, they don’t have it. You have to have that passive extension, and then also the active components, to transfer over to the functional components.

A few important things here to just note: if your knee feels like it hits a hard block, like something is physically in the way instead of a stretch, don’t keep forcing it. Get an experienced clinician or have your surgeon look at it. Just have someone look at it. Again, with enough overpressure, you could probably get the knee to look like it has some hyperextension or can get there, but there can be enough force to make it feel that way in a moment. You have to track it over a period of days to see whether it regresses back and whether it improves at all.

This is something that we notice too: when people walk into a surgical visit, for example, or even a PT visit, and there’s a goal of really trying to overpressure and convince ourselves there’s more there, I can jam your knee into hyperextension and get a little bit more out of that. Everyone knows this feeling. But we have to track the data over time. It’s not just that one moment. What does the data look like across days and weeks, and has that improved at all? If it hasn’t and it rebounds back, then we need to start talking about what’s going on. If you suddenly lose that extension you used to have, or maybe the knee swells up or feels warm, same thing. We have to assess and see what’s happening here. And if you have calf pain, swelling, or warmth after the surgery, we gotta get that checked, right? So those are important things to look out for. 

I’ll also say this: do the audit yourself because it’s helpful. But I suggest doing it with someone who’s experienced with this process because they can make more sense of this information. This naturally creates a one, two, three-step process for me whenever I hear passive matches the other side, active does not; passive and active both fall short; versus both matching the uninvolved side. This automatically makes our brains go through a process to understand, okay, this is what our action plan is going to look like, and it’s going to look very different across these different outcomes.

Make sure you have someone who is experienced in ACL rehab, a physical therapist, to help get clarity on what it means, and not just trying to troubleshoot it alone. This is something that you can’t necessarily always stretch your way out of, or hope comes with time, especially if that passive is not accessible. That is where we need to really play detective and figure out: is it more muscle-based? Is it more that the joint is just really irritated and swollen and it won’t access that position? Over time, as we put a plan in place, get it calmed down and quiet, and the muscle’s not guarding, can we essentially stretch into that position with proper techniques, exercises, and frequency? Or is this something that just won’t budge? It’ll rebound back. If so, then we gotta look at this further. And yes, I’m talking about scar tissue or a cyclops lesion that could be playing into this.

One of our athletes described it as getting a sweater stuck in a doorjamb. That’s kind of how it feels. When he goes to close the door, that’s kind of how it feels trying to get into extension, like there’s a sweater in a doorjamb. Our team was just like, “Man, that’s a really good way to put a cyclops lesion,” because you can kind of get it there when you forcefully push, but it just doesn’t stick into that extension.

The last thing here is just knowing extension can regress. You work on it, you get it, and then you just put it in the rearview, right? That’s the thing that happens. You don’t check it, and it slips away. You need to make this a part of your regular kind of audit routine of your knee. A heel pop test on both sides regularly. It takes no time whatsoever, and once you get it, maintain it. That is something I show every athlete. All of our athletes do it. We have audits where they just look at this and are able to look at it through the process and see if it feels off or not.

Sometimes people do have that regress a little bit, and it might just not have had enough attention, especially when you get more into heavier loading phases. If they’re matching, great. If not, we adjust, and we need to work on it and make sure it is maintained throughout this process. That is your knee’s normal.

Here’s what I want you to walk away with. Extension is priority number one, and it does not fix itself with time. The goal is your uninvolved side. Do not get to zero or whatever’s flat on the ground. We need it to match your uninvolved side, with the caveat of hypermobile people.

The test that we’re going to be looking at is the heel pop test. We’re going to look at it actively and passively on both sides, write down what you feel with that, and then also record it from the side and from the bottom of your feet. Let’s see what the differences are. Let’s put some objective numbers around this.

If passive isn’t there, active cannot get there. Find out why. Play detective and work with your physical therapist. If they say it’ll get better with time, or it’ll iron out, or zero is fine, then go find a different PT. I would say most good knee and ACL PTs are not the ones saying that. They’re going to be like, “We need to get it matching the uninvolved side.”

If passive isn’t there, active can’t get there, and you need to figure out why. Don’t kick the can down the road. Get it assessed, get a plan in place, and I promise you, it can save you a headache six months down the road, nine months down the road, or, if you’re like this guy, 12 months from that first imaging and now having to go get this thing cleaned out. 

No one paid attention to it earlier, and then we just had some imaging done again as he joined to be able to say, “Okay, this is the problem. Let’s go get it cleaned out, and let’s hit the road to recovery.” That’s going to fix the issue, and therefore he’s going to be able to put it behind him. But that could’ve been done before.

There needs to be a plan in place and someone who is checking this for you and connecting the dots. Then just recheck it regularly. If it regresses, put a plan in place and work on some of those things. It is such a foundational piece of this ACL rehab process. And if you take one thing from this, just make it that: good enough does not work in extension. You gotta make sure you get it back.

And if you want help auditing this, if you feel like you’re the one stuck in this, we’re here to help. You know where to find us. We have our information in the show notes. We are helping many ACLers navigate this process who are having such challenging issues, or people are not listening to them, or they feel like they’re crazy, and we’re connecting the dots on these things and trying to help you figure that out. Or if you’re just feeling like you need structure, you’re feeling like you need targets, we are here to help or even point you in the right direction so you feel like you’re not the one who is having to shoulder this process.

Most importantly, advocate for yourself because this world and this kind of space is messy, and it’s really important to make sure that you are the one who can look out for your knee. It’s something that is so important for the short term, but especially the long term, and especially for our mental health.

We all need to get back to where we want to be, and it starts with making sure that we do this process right and have the right people alongside us. If you need anything, we’re here to help. I hope that this was helpful. Do your knee extension audits, and if you find another ACLer who is having issues, send this to them as well. Otherwise, I’m going to close out this episode. This is your host, Ravi Patel, signing off.