Why Can't I Straighten My Knee?

Understanding Why a Knee Gets Locked

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A "locked knee" means you can't straighten your knee or you can't bend it. It 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 healthcare provider must find the cause of a locked knee, and several are possible. A condition like a meniscus tear may be physically preventing the knee from moving, or a case of tendonitis causes so much pain that the knee cannot bend or extend normally.

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

Causes of a Locked Knee

A locked knee can be caused by a condition that causes pain or from a physical issue preventing movement. Orthopedists and other healthcare providers may refer to the inability to bend or straighten your knee as either a true locked knee or a pseudo-locked knee.

True Locked and Pseudo Locked Knees

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.

Meniscus Tear

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.

 Anterior Cruciate Ligament (ACL) Tear

An anterior cruciate ligament (ACL) tear typically makes the knee unstable, which may be a reason for why you can't straighten a knee. It also may cause enough pain to prevent you from doing so.

A Grade 3 ACL tear typically will require surgery to repair, but it's important to have the knee pain assessed for its severity and properly diagnosed. Other treatment options may be possible.

Knee Fracture

A knee can be fractured or you can experience a dislocation, when the joint is moved out of its normal position. These injuries are likely to be trauma-related and require urgent assessment.

In most cases, the cause of a knee fracture is a direct blow or fall onto the knee. Pain, difficulty straightening the leg, bruising, and swelling can occur. Sometimes there's visible deformity and the reason for why you can't straighten a knee is more clear.


Severe bursitis is an inflammation of the knee's bursa, a fluid-filled pad that cushions the joint.

A common cause of prepatellar bursitis, with swelling and pain that affect the top of the kneecap, is work that requires kneeling, like gardening. It also can be injured from a fall or while playing sports.


Severe tendonitis is an inflammation of the tissue connecting muscle to bone in the knee. The inflammation is often seen in people who jump while playing sports like basketball and in runners. The tendonitis can make it difficult to bend the knee.


Two very different kinds of arthritis, both gout and rheumatoid arthritis (RA), can cause pain and inflammation that affect your knee mobility. RA is an autoimmune disease that causes symptoms because the body's own immune system is attacking the tissue.

Gout typically affects the big toe but can cause symptoms at any joint, including the knee. It's caused by a buildup of uric acid in the body, with diet and metabolism playing important roles in its development.

Diagnosing a Locked Knee

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, they may order blood tests including:

Once these tests measure the markers for these conditions, they can contribute to an accurate diagnosis for why you can't straighten a knee.

Should I Go to the ER if I Can't Straighten My Knee?

You may need to seek emergency care if you suspect a fracture, experience extreme pain, or can't bear weight on the affected leg.Additional symptoms, like an altered mental status from the same fall that caused knee injury, may need ER care. Otherwise, contact your healthcare provider for an exam and diagnosis.


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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.

True 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
  • 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.


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, your healthcare provider may recommend ice, rest, and over-the-counter painkillers.

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 it's 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 occurs, you may first 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.

  • Does osteoarthritis in older adults make it hard to bend the knee?

    Yes, age-related osteoarthritis (OA) changes can make the knee stiff and limit mobility. The RICE principle (rest, ice, compression, elevation) may work, but in some cases surgery and physical therapy may be needed to treat the knee. Your healthcare provider can discuss the options.

5 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. American Academy of Orthopaedic Surgeons. Common knee injuries.

  3. Reinking MF. Current concepts in the treatment of patellar tendinopathyInt J Sports Phys Ther. 2016;11(6):854–866.

  4. American Academy of Orthopaedic Surgeons. OrthoInfo. Patellar (kneecap) fractures.

  5. American Academy of Orthopaedic Surgeons. 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.