Why Your Knee Locks and What You Can Do About It

• Updated on: 2020-04-28
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A "locked knee" is a term used to describe an inability to either bend or straighten their knee. A locked knee can be a very painful condition that limits not only the ability to bend, but also the ability to walk, step up, or even sit down comfortably. Finding relief from the discomfort of a locked knee is dependent on first determining the cause of the problem, and then addressing the source of the problem to allow the knee to bend normally again.

There are two general types of locked knees. The locked knee can either be caused by a mechanical block to knee motion, or a locked knee can be caused by pain that is too severe to allow knee motion. The first step of your physician is to determine if the knee is not bending as a result of pain, or a result of something inside physically impeding motion of the joint.
Causes and Diagnosis

When a locked knee is caused by a mechanical block to motion, there is something that is physically being caught within the mechanism of the knee. Often the cause of a locked knee in this situation is a "bucket handle" meniscus tear.1 When this type of meniscus tear occurs, a large fragment of the torn meniscus can become wedged within the knee, preventing normal movement of that knee.

You can also have a locked knee when you have severe pain with any knee motion.2 While it may be difficult for a patient to determine whether or not there is a physical block to their knee motion, or if pain is the issue, a good physical examination can usually separate these two types of problems.

Sometimes a test can be helpful to determine the cause of a knee that will not bend. X-rays of the knee joint can show loose bone, fractures, and swelling within the joint. They can also be helpful when they are normal to ensure there is nothing more serious taking place in or around the joint that is preventing the knee from bending. If an X-ray does not help lead to the diagnosis, a test called an MRI can also be helpful. MRIs can show cartilage, ligament and tendon problems. Specifically, torn or abnormal meniscus tears, or loose cartilage, will typically show up on an MRI examination.
Treatments Available

When there is a physical block to knee mobility such as a bucket-handle meniscus tear or a loose piece of cartilage, the typical treatment is to remove the impediment with arthroscopic knee surgery.1 Sometimes your doctor may try injecting the knee with a local anesthetic to alleviate the discomfort and try to move the impediment, but typically the cartilage or meniscus will be removed.

If the issue preventing motion is just a pain issue, then the pain needs to be managed. Typically simple pain-relieving treatments such as ice, anti-inflammatory medications, and rest, will allow the pain to subside.2 If these simple steps are not helpful, often an injection of a local anesthetic or a cortisone shot can help to reduce the discomfort to a point that allows you to bend the joint again.

Seldom are prescription pain medications necessary to alleviate the pain of a locked knee, and these medications should be used with caution because of possible side-effects.

The good news is that there are effective treatments for people who have a locked knee. If you are unable to bend your knee joint, you should be evaluated by a physician who can determine the source of your problem, or if further tests are needed to determine the cause. Once the underlying problem has been identified, a treatment plan can be initiated to get you moving again.
A Word From Verywell

Having a knee that's unable to be bent, also called a locked knee, is typically a sign of a significant problem with the knee joint. Determining if pain is limiting mobility, or if there is something physically stuck inside the knee joint, can help to determine the most appropriate steps in treatment. Fortunately, most people with a locked the are able to recover the mobility with the proper treatment.