Knee extension (knee straightening) is by far one of the most important goals to achieve early on in your post-op ACL rehab.
Why? Because it is essential for getting back to every day activities without lingering dysfunction- even walking! However, the clock is ticking on how long you have to get that full knee extension. It’s something we need to get early on or risk not getting it at all.
Ideally, I like to see full knee extension 7-10 days after surgery. It’s important to note that everyone is different, and this isn’t to say after day 10 we won’t see improvement.
“Full” knee extension also varies from person to person depending on the amount of hyperextension they have. Most people have about 5-10 degrees of it. My minimum goal for extension in all my patients is 0 degrees, but ideally we want that hyperextension, too.
I’ve outlined my favorite ways to work on increasing extension range of motion (ROM) with my patients below:
Low Load, Long Duration Stretching:
This exercise will be the bulk of your knee extension training and should be priority #1. I typically prescribe this exercise the first day I see a patient post-op at 3-4x/ day for 5-10 mins, depending on tolerance.
The key for this stretch is for it to be tolerable. If your muscles are constantly fighting against you the whole time, we are likely going to get a lot of pain and less progress.
Here’s how I progress low load, long duration stretching for my patients:
- With the foot propped up on a table or chair, start with just letting gravity push the knee down
- If that’s tolerated well, we’ll add a light weight to the bottom of the thigh. (not directly on top of the knee cap)
- If that’s tolerated well, we’ll add a calf stretch with a yoga strap
- Finally, if all is going well with these progressions, I’ll have my patient overload with a quad set. (actively contracting the thigh muscles to push the knee down)
This remains part of the home exercise program until we consistently have full extension at the beginning and end of each clinic visit without need for hands on work from me.
Fluid accumulation in the knee is inevitable following ACL surgery. Our goal is to control it to the best of our ability to decrease the negative effects it has on your progress.
Swelling can limit your extension by making it more difficult for your knee to move properly. It can also limiting how much your quads can contract. (your quads are responsible for pushing your knee “down” and straight)
The 3 best ways to control swelling are to use:
- Gravity (keep your knee elevated above your heart when possible)
- Compression (compression stockings, vasopneumatic compression boots)
- Movement (ankle pumps, mini squats when cleared)
You can learn more about controlling post-op edema (swelling) here.
Soft Tissue Mobilization:
There are 2 main muscles groups that attach to the back of your knee and can limit your knee extension when they get tight: your hamstrings and calves.
Following surgery, these muscle can be stuck in “protection mode”, meaning they are trying to keep your knee slightly bent. While this position is typically more comfortable, it’s not doing us any longterm favors.
Foam rolling, massage or using a percussion massager (like the Hypervolt or Theragun) can help to loosen up the restriction, making it easer to get full knee extension.
Your quads (the muscles on the front of your thigh) are responsible for extending your knee, so it is essential we train them up early on in rehab. Quad sets are a great way to start and are typically safe to do immediately post-op.
To perform a quad set you will want to be seated or lying down with your knee straight. With your knee extended, try to actively “push your knee straight down” using your muscles. I also like to progress these to a standing version when appropriate, so your quad gets comfortable contracting while holding up your body weight.
Adding a quad set to your low load, long duration stretch it a great way to push for additional extension.
This is an exercise you don’t want to jump into until you’re steady on your feet. Even after patients are off their crutches, I’ll have them hold on to something for support the first few times.
You can walk backward on a treadmill or on flat ground. You’ll want to think about taking big steps backward, encouraging that knee into full extension and then bringing the other leg to meet it. You can add cones and hurdles for additional cuing.