Episode 187 | Why Your Terminal Knee Extensions Aren’t Working: A Common Mistake in ACL Rehab

What’s up guys? I’ve got a super short one for you today, mostly because I have really just done it overboard on the previous podcast episode—being super long. You guys deserve a short one and this is what you’re going to get.

Today, I am talking about Why Your terminal Knee Extensions Aren’t Working: A Common Mistake in ACL Rehab. I see this all the time and this actually builds off of the previous episode, of the role of the screw home mechanism in terminal knee extension. If you want to catch that episode, go check it out because it’s going to help to hammer home what it is I’m going to talk about today. But it will be less technical today, but it will still be very helpful. Go check that out, if you will, and then come back over to this episode. So then that way it gives you a little bit of groundwork of understanding the motion at the tibia and at the femur and the way the knee interacts. 

Let me give you just a short little bit of what’s important whenever the knee goes into extension; going from bending into full knee extension, and that last 20 degrees towards full knee extension. Your tibia or your shinbone is going to externally rotate on your femur bone or your thigh bone, and is going to have sort of turn or this twist externally in order to do the screw home mechanism, which is basically where it just kind of locks into place. And then to unlock, the tibia will internally rotate and then bend the knee. There’s a slight turn of the tibia and then it’s going to start bending. And so that’s called the screw home mechanism. How does this relate to your terminal knee extension movements and the mistake that I see. So, think about the most common physical therapy exercise that you probably see besides quad sets and straight-leg raises, especially post-op is going to be a TKE, which is called a terminal knee extension (banded terminal knee extension) to be very specific. This is something where every one of you have probably done this, especially if you’ve gone to a PT clinic. It’s where there is a thin band that is anchored to something in front of you, at the height of your knee and it is wrapped around the back of your knee. You are standing and then all you’re doing is bending the knee a little bit and then you’re extending it, straightening it out and you’re going to contract your quad to do a quad set. Essentially, this is helping to work on terminal knee extension of the knee joint activating the quad. 

Now, this is where I want to talk about the common mistake that I see with this and how we can really improve this terminal knee extension and get so much more out of this movement just by a small change. One thing that’s going to be important here is that they don’t necessarily focus on what the foot is doing. It’s on the physical therapist for us to make sure that we are guiding the athlete in terms of all the different moving pieces and just to make sure that the whole chain of the movement is doing its job. There’s no compensations or making sure that like one joint isn’t restricting another joint. And so then therefore we want to make sure that this is taken care of, and this is a closed kinetic chain movement, which means the lower leg and especially the foot is going to be rigid on the ground. Therefore, it’s easy for someone to go through this motion. 

One is going to be an intent, is making sure you’re just not going in and out of this motion without being very intentional about it. Because this can really help to restore that terminal knee extension, which is something a lot of athletes struggle with post-op. One thing that we see is that the athlete will keep the foot rigid. What this means is that when they go to bend the knee, so let’s say they’ve already like squeezed the quad into full terminal knee extension. When you go to relax, it’s not just relaxing and then just like, all right, go back into it. We actually want to let the knee to travel forward and let the foot collapse a little bit, meaning let it pronate a little bit; let that arch collapse. And what that’s going to help do is let that tibia move and rotate a little bit. 

If we have a rigid foot, it’s going to lock up the tibia and it’s not going to allow that thing to rotate like we want to. Let the foot move and what will happen with this is that we want to make sure that that foot pronates as you bend or flex that knee so that arch is collapsing. You should see that thing disappear as you go to bend the knee. And then it should supinate, or you should be able to see your arch again forming as you go to straighten and extend the knee into that quad set and really having that band taught and squeezing the quad as hard as you can. This allows for that internal and external rotation of the tibia, which improves flexion, especially with internal rotation and extension with external rotation at the knee joint. If your foot is rigid or let’s say that it is stuck in pronation, then you’re going to have a hard time getting that full knee extension because you actually want it to supinate, to allow the tibial to externally rotate. 

Again, coming back to that screw home mechanism to allow for full knee extension. And then vice versa, if it feels like it’s stuck in super nation. We need that tibia to internally rotate. It needs to actually pronate or let that arch collapse while you’re flexing the knee, otherwise that knee flexion is going to be limited if your foot is locked into supination. So that is the thing that is always challenging with this because people are always struggling with finding positions in joint angles. There are a lot of other factors like strengths playing into this. But when you have some soreness around the knees, and you’re trying to get your quad stronger, but then  this can create this cycle of, you can’t really do that because you’re dealing with issues at the knee. Therefore, you can’t get stronger. We need to really try to focus on opening up the joint mobility, especially in isolation, and then integrating that all together, to make sure that everything is moving fluidly. 

Because guess what, when we are moving and when we are, especially in sport and activity, it’s not these isolated movements, it’s a whole kinetic chain and the way that the body interacts, even especially at the knee hip and the ankle, they’re going to flex, extend and do all the things together. If we don’t have the rotational components alongside it, then you’re going to have to try and find that other places, or there’s just going to be some leaks of the energy and also the forced transfer. So that is going to allow us to have more options for movement as well, because that makes you a little bit more dynamic in a situation, instead of just being so rigid with one particular direction in motion. 

If we have a bunch of options that we have trained and have access to, it allows us to disperse the stress better, and that’s going to also be helpful for long term for injury prevention and more importantly for performance enhancement. So that is going to be some key players to this. Work on making sure you’re doing some tibial rotations. You could do open chain type work and then closed chain type work, doing some foot mobilizations, getting it moving. And then making sure that this is helping with your flexion as you go to internally rotate and also extension as you externally rotate, to really reinforce that screw home mechanism and for you to be able to load your knee and your quads and your whole entire lower bodies. 

This is one of the things that I see with terminal knee extensions that doesn’t work really well, is that people go through the motions. They’re not cued very well. I think we just kind of learned this as in protocols, through PT school and people see them and like, okay, cool, that’s just like a basic post-op exercise. But let’s be intentional about what we’re doing because we can get so much more out of it, especially for our ACLers who are having trouble with getting that end range knee extension, especially that screw home mechanism where the tibia can’t externallyI rotate. Well, maybe it’s because you’re keeping that foot super rigid and it’s not being able to pronate and it’s not being able to supinate. Therefore, it’s impacting rotation of the tibia, and then therefore it’s impacting your extension, your flexion, and that screw home mechanism. 

Being able to follow some of these little details will have such a huge return and more importantly, allow you to access the range of motion and the positions that you need to in order to keep training and moving your ACL rehab along in the process. All right guys, I did one, a short one. You’re welcome. I’m going to hop off here. If you want to show me some love, leave a review. Otherwise, I will catch on next time. This is your host, Ravi Patel, signing off.