Knee locking is when the leg gets stuck in one position, making it impossible to bend or straighten the knee.
A locked knee may only last a few seconds, it may last longer. It all depends on what is causing it.
There are two different types of locked knees:
Here, we will look at the common causes of both types of knee locking up and then go on to look at the best locked knee treatment options, including how to unlock a locked knee!
True knee locking is caused by something getting stuck inside the joint that physically prevents the knee from moving.
The knee joint is designed to bend up and down, flexion and extension, and rotate slightly. If something gets caught inside the knee joint, it blocks the movement and the leg gets stuck - think of it like a door stop. When this happens, the knee is totally blocked, unable to move at all.
It often takes a few minutes of gently moving the knee, or as patients often say “waggling it about”, to unlock a locked knee but sometimes professional intervention is needed to get the fragment to move out of the way, before you can move the leg again.
True knee locking is usually caused by:
A meniscus tear is, by far, the most common cause of the knee locking up.
The meniscus is a thick piece of cartilage which lines the knee joint to provide cushioning and allow smooth movement.
If the cartilage gets torn, usually from twisting awkwardly or from gradual wear and tear, the loose fragment may get stuck in the joint stopping it from being able to move.
As the knee moves around, if the cartilage flap is large enough, it can get wedged in the wrong position, blocking the joint and causing knee locking. Your knee just won't be able to move until you are able to manoeuvre the flap out of the way, freeing up the joint.
The most common type of meniscus tear that causes knee locking is known as a bucket-handle tear. This is where part of the cartilage gets torn, but remains partially attached producing a movable flap, usually "C" shaped.
If you find your knee locking up and popping, it is most likely due to a meniscus tear.
You can find out more about the causes, symptoms and best treatment options in the meniscus tear section.
Another thing that can block the joint and cause true knee locking is when a small fragment of bone breaks off from the knee joint, known as a loose body, and floats around.
As with a meniscus tear, if it moves into the wrong place, it can get wedged in place and cause the joint to lock in a specific position.
True knee locking from a loose body may be caused by:
True knee locking may or may not be accompanied by pain, depending on the cause. It is usually extension that is limited in true knee locking, preventing you from being able to fully extend your leg.
Pseudo knee locking is almost always linked with pain. If knee pain is severe enough, then the body’s protective mechanisms kick in, limiting the movement as the body tries to prevent any damage being done. It usually does this by causing the muscles to spasm, holding the leg in position.
The difference from true locking is that there is nothing actually stuck inside the joint, and whilst the knee may at first appear to be stuck, it usually unlocks quickly. There is often more of a “catching” sensation which inhibits movement but quickly disappears rather than the knee locking up completely.
Pseudo locking can limit both flexion and extension, bending and straightening the knee, whereas true locking is usually a block to extension only.
The most common causes of pseudo locking at the knee include:
Appropriate knee locking treatment will depend on whether there is something getting stuck in the joint or not. Assessment by your doctor or physical therapist should be able identify what is causing the restricted movement.
Treatment for locked knees may include:
Check out the Locked Knee Treatment section to find out loads more on how to treat and prevent knee locking as well as How To Unlock A Locked Knee.
Knee locking is where the knee gets stuck and can't move properly
Pseudo knee locking is a protective mechanism usually caused by pain, swelling and/or muscle spasm
True knee locking may or may not be painful, whereas pseudo knee locking is usually always painful
Knee extension is limited with a truly locked knee whereas both flexion and extension are limited with pseudolocking
Locked knee treatment may involve exercises, knee injections and, in some cases, surgery.
You may also be interested in the following articles:
Page Last Updated: 02/06/23
Next Review Due: 02/06/25
1. The Journal of Pediatrics: Locked Knee in a 15-Year-Old Girl: The Knee Examination. June 2017
2. Healthline: Why Is My Knee Locking? April 2018
3. British Medical Journal Case Reports: Locked bucket-handle tears of both medial and lateral menisci with simultaneous anterior cruciate and medial collateral ligaments injury. June 2011