Why Your Knee Locks and What You Can Do About It

True Locked Knee vs. Pseudo-Locked Knee

A "locked knee" is a term used to describe an inability to either bend or straighten the knee. A locked knee can be a very painful condition that limits not only the knee's range of motion—the degree to which the joint can move—but your ability to walk, step up, or even sit down comfortably.

To find relief, your doctor must first pinpoint the underlying cause of a locked knee. This could be something physically preventing the knee from moving or something that is causing so much pain that the knee cannot bend or extend normally.

This article explains the two major causes of a locked knee, how they are diagnosed, and what can be done to treat them.

Causes

Orthopedists, doctors who specialize in the diagnosis and treatment of the musculoskeletal system, refer to the inability to bend or straighten the knee as either a true locked knee or a pseudo-locked knee.

True Locked Knee

A true locked knee is one caused by mechanical issues in the joint. In other words, there is something that is physically getting caught within the mechanism of the knee that impedes movement.

Often, the cause of a true locked knee is a so-called "bucket handle" meniscus tear. With this, a large fragment of the torn cartilage in the knee (called the meniscus) can become wedged within the joint, preventing normal movement.

Pseudo-Locked Knee

You can also have a locked knee when you have severe pain with any knee motion. This is common referred to as pseudo-locked knee.

A pseudo-locked knee occurs when severe knee pain causes the knee muscles to spasm and contract. The knee is not physically locked but is, nevertheless, unable to move as it should.

A pseudo-locked knee is an automatic defense mechanism intended to discourage movement of the knee so that no further harm can be done.

There are many possible causes of a pseudo-locked knee, including:

  • Knee fracture or dislocation (when the joint is moved out of its normal position): These injuries are likely to be trauma-related and require urgent assessment
  • Severe bursitis: Inflammation of the knee's bursa, a fluid-filled pad that cushions the joint
  • Severe tendonitis: inflammation of the tissue connecting muscle to bone in the knee
  • Acute attacks of gout or rheumatoid arthritis

Recap

A true locked knee is when a knee cannot bend or straighten due to a mechanical problem in the knee itself. A pseudo-locked knee is when severe pain—due to a dislocation or bursitis, for example—makes it impossible to move the knee.

Diagnosis

A good physical examination can usually differentiate whether you have a true locked knee or a pseudo-locked knee. This includes a review of your medical history and the events that led up to the issue.

Tests That Can Diagnose a Locked Knee
Verywell / Brianna Gilmartin

An X-ray of the knee is commonly ordered. It can show whether there are any loose bones, fractures, or acute swelling within the joint.

If an X-ray is inconclusive, a magnetic resonance imaging (MRI) scan can be ordered. MRIs are better able to visualize soft tissues and can show if there are any cartilage, ligament, or tendon problems. Meniscus tears will typically show up on an MRI examination.

If a provider suspects an infection or an autoimmune disease (i.e., one in which the immune system mistakenly attacks healthy cells), C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and rheumatoid factor (RF) blood tests can be ordered to measure markers for these conditions.

Recap

The diagnosis of a locked knee typically involves a physical exam, a review of your medical history, and an imaging study like an X-ray or MRI. Blood tests can also help narrow down the possible causes.

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Treatment

The treatment of a locked knee depends on the underlying cause as well as the severity of the condition. There are standard approaches for both locked and pseudo-locked knees.

Fortunately, most people are able to fully recover with the proper treatment.

Locked Knee

Sometimes your healthcare provider may try injecting the knee with a local anesthetic to alleviate discomfort and try to move the impediment.

However, the cartilage or meniscus causing the problem will typically need to be removed with arthroscopic knee surgery. This involves a few small incisions and the use of a camera to see inside the knee so that a surgeon can view the affected area and complete the removal.

Pseudo-Locked Knee

If the issue preventing motion is pain, then that pain needs to be managed. This typically involves conservative treatments such as ice packs, rest, and over-the-counter nonsteroidal anti-inflammatory drugs (NSAIDs).

If these simple steps are not helpful, an injection of a local anesthetic or a cortisone shot can help reduce the discomfort to a point that allows you to bend the joint again.

Prescription pain medications are seldom used to alleviate the pain of a locked knee and should be used with caution due to possible side effects.

Recap

Arthroscopic knee surgery is typically recommended if a meniscus tear is the cause of a locked knee. If pain is the cause, ice, rest, and over-the-counter pain killers are the standard first-line course of treatment.

Summary

The inability to bend or straighten the knee may be the result of a true locked knee (in which torn knee cartilage becomes wedged in the joint) or a pseudo-locked knee (in which severe knee pain triggers a defensive reaction that impedes knee movement).

A physical exam, a review of your medical history, and imaging tests like an X-ray or MRI can usually reveal the underlying cause.

If the cause is a meniscus tear, arthroscopic knee surgery is generally advised. If pain is the cause of a locked knee, ice, rest, and over-the-counter painkillers are usually recommended.

A Word From Verywell

Having a locked knee should never be considered normal. Even if it is only temporary and quickly resolves without treatment, it is still in your best interest to have it checked out.

The incident may hint at a more serious concern that requires treatment.

Frequently Asked Questions

  • Can you walk on a locked knee?

    It depends. You may be able to walk on a locked knee caused by a meniscus tear if it does not block joint movement. If the locked knee is caused by an issue that makes bending and straightening impossible, you may not be able to walk on it—or at least not without extreme pain.

  • Where is the pain felt with a meniscus tear?

    When a meniscus tear first occurs, you will likely feel a pop in your knee. After the initial tear, you may feel pain directly in the joint, especially when putting pressure on the knee. You may also experience swelling and a feeling like the knee is going to "give out" when attempting to walk.

2 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Goodman AD, Chase A, Owens BD. Locked knee in a 15-year-old girl: The knee examination. J Pediatr. 2017;185:245-245.e1. doi:10.1016/j.jpeds.2017.02.037

  2. OrthoInfo. Arthritis of the knee.

Additional Reading

By Jonathan Cluett, MD
Jonathan Cluett, MD, is board-certified in orthopedic surgery. He served as assistant team physician to Chivas USA (Major League Soccer) and the United States men's and women's national soccer teams.