10 Tue

The little muscle in the back of your knee

The little muscle in the back of your knee

Paul Kochoa, PT, DPT, OCS, CGFI



Recently I had a patient come in complaining of pain right in the back of his knee.  He said it started after doing heavy leg presses and locking his knees out.  It only hurt when he completely straightened his knee, not when he bent it, and also when he started walking after getting up out of a chair.  He was concerned that he tore his hamstring muscle or a ligament in his knee.  I assured him that his symptoms would be worse if that was the case.  And that’s when I introduced him to the popliteus muscle.  

The knee is generally a hinge joint.  It bends and straightens, pretty straight forward.  Most people think that rotation to the knee results in ligamental injuries like an ACL tear.  But most people don’t think about the normal rotation that occurs in the knee in the last couple degrees of terminal extension (when you lock out your knee all the way).

When you completely straighten your knee, either when you’re sitting or standing, there’s a rotation that occurs in the knee to completely lock it out.  It’s because the bones in the knee (the bottom end of the femur and the top of the tibia) are not completely even and flat.  One side is bigger than the other, so to completely straighten the knee, there’s a “screw home mechanism”.

Here’s a great video from superstar physiotherapist Kelly Starrett about this mechanism:


The popliteus muscle is responsible for “unlocking” the knee and allowing you to come out of full knee extension.  If there’s an injury to this muscle, or if it’s tight or strained, the last couple degrees of full knee extension may be compromised and painful.  This compromised position may result in more knee pain in the front of your knee or movement dysfunctions that may even create pain in your hip or back.

That’s why when you’re doing loaded squats or a leg press, you shouldn’t completely lock out your knees.  Under load, that’s a lot of work for that small muscle to do, and it places more stress on your knee joints.  Also walking around with a knee that doesn’t straighten all the way is bad news.  You’re just asking for more damage.

If you’re having popliteal muscle issues, get it checked out by a physiotherapist.  There’s a lot we could do to get it fixed. There’s no reason to let it go and hope it gets better by itself.  Give us a call at 973-270-7417.  Our offices are located within the YMCA locations in Madison and Summit, NJ.  You do not need to be a member of the YMCA to visit with us.



Image courtesy of Toa55 / FreeDigitalPhotos.net

Comments are closed.

Call Now