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
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.
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.
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.
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.
