“Help! I can’t straighten my knee!”

Posted on September 3, 2015


For years now, I’ve extolled the importance of working on knee extension 1) after knee injury 2) after knee surgery. This has been particularly emphasized in my reconstructive ACL and meniscus injury writing.

I wrote a manual on the first month of ACL rehab, where I cover knee extension fairly thoroughly.

However, not everyone who has trouble with this is in the first month of ACL recovery, or has an ACL history. Losing knee extension is common in practically every knee injury. Whether a good sprain, a scope procedure (arthroscopic surgery), or a knee replacement. It’s the first thing lost, and the first, and most important, thing to gain back.

I wanted to put something together to help a broader group of people suffering from this malady. I do have a good amount written on the importance of working on knee extension, but I don’t think I’ve done a good enough job detailing how to do this. Nor why it’s so crucial to focus on immediately. (Hence, this post, which is posted the same day as this.)

This manual, Regaining Knee Extensionwill cover the A – Z on recovering lost range of motion. If you can’t straighten your knee, this should help.

You can get it here- Add to Cart

What’s covered:

-What is full extension?

-> Full extension is not only the ability to straighten your leg. You want more than that. Brief words on why.

-Why is it important?

-> Sure, there is the obvious benefit of being able to straighten the leg. But why is this so crucial, so early? (More info below too.)

Note: This is not anatomy heavy or technical stuff. I think some rationale for why you’re doing something often helps, but the point of this manual is “What do I do?” and “How do I do it?” opposed to “Why do I do that?” The point of this manual is to get to work, and get healthy. Not to learn the finer points of physical therapy for the knee. 


-> When you can’t move your knee like normal, other body parts need to move more. If you can’t straighten your knee, something else has to straighten more. A couple animations are shown illustrating how something like the back can start to get ticked off when the knee can’t move like usual.

Timing matters

-> I cover this for free here. (Does get a little anatomy heavy.) I can’t emphasize this aspect of things enough. When it comes to flexibility, strength, exercise, and things part of the physical activity world, there really is very little which is time sensitive. Few weeks of bad eating? Eh, no big deal. You’re back on track within the month. Month of no exercise? Eh, not great. But in a week you’re back in the swing.

Not with knee extension though. Time matters. It’s not like every second matters. But days easily turn to weeks, and once you’re at a week or two…things start getting harder.

-How to do it-

Massive caveat

-> This is in the manual as well, as it bears repeating:

“First, if you’re someone recovering from a knee replacement, this may work, but it may not. With a knee replacement, you always have to consider hardware placement as an impediment to range of motion. Some have to have a revision surgery in order to regain full range of motion.

Second, if you’re someone whose knee has locked on them, someone where you feel something physically blocking your knee from fully extending, like something has moved and is now in the way, this will either not work as well, or not work period. You should see an orthopedist ASAP, and likely get into surgery ASAP. (The emergency room probably won’t do anything though.)

That is often a displaced meniscus tear, and short of being able to get the meniscus to reduce (go back into place, which is sometimes pure luck), that thing isn’t going to budge, nor do you want to force it to. You can still work on things in this manual very carefully, but know full extension is not happening until that blockage is taken care of. Get into an ortho immediately. If you tell them what’s going on -it’s better to do it in person with crutches than on the phone- they will likely fit you in as an urgent appointment.

This is not something to mess around with. You don’t want to be waiting a month or two to take care of something like this. Once it’s taken care of, this manual should work quite well!

The goal

-> How quickly are we trying to get this extension back? How soon is reasonable?

Caveat to the goal

-> Making the distinction between those who were recently injured, and those who haven’t had full knee extension for a while.

Regaining passive extension

-> Including a video going over the main exercise to regain extension. No special materials or equipment are needed.

Regaining quadricep activation

-> It’s common for the quadricep to fall asleep after knee trauma. The quadriceps help extend the knee, so we want to insure they’re awake.

Regaining active extension

-> Discussing why we start with passive extension and quadricep activation first, before moving on to active extension. Again, no special equipment is needed. Whatever you have around your apartment / house will suffice.

Passive extension is something else doing the work. Gravity, a weight, a person; active extension is the leg doing the extending.

-Making your daily life more extension friendly

-> You have a good idea of what to do exercise wise, but how do you go about your day? You can exercise and work on your extension for an hour everyday, but if you’re stiffening things up the other 23 hours, you’re fighting a battle you don’t have to.


-Laying down (and sleeping)

Waking up in the morning


^ Modifications for all the above to help make one less likely to lose extension.

-Checklist: How a typical day might look

-> I go through an imaginary day, hour by hour (sometimes minute by minute), detailing how to make sure you regain full extension. This will encapsulate everything discussed beforehand, but with an example of how to implement it into daily life.

The manual is $10: Add to Cart

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