Locked knee occurs when a person cannot bend or straighten their knee. Causes include injury to the area and inflammation of the joint.

The knees are two of the most important joints in the human body. Aside from supporting a person’s body weight, the knees enable everyday activities, such as standing up, walking, and climbing stairs.

As a result of such frequent use, the knees are prone to injury and degeneration. Both can lead to locked knee.

There are two types of locked knee: pseudo and true locked knee. Keep reading for more information about their causes, symptoms, and treatments.

Locked knee occurs when a person is unable to either bend or straighten their knee. There are two types.

Pseudo locked knee

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Injury is a possible cause of a locked knee.

Pseudo locked knee occurs when severe knee pain triggers the knee muscles to spasm and contract.

It is an automatic defense mechanism that the body uses to discourage movement of the knee. Restricting the knee in this way helps prevent further damage.

Although muscle tightening and swelling make bending or straightening the knee painful, the knee joint itself is not physically incapable of moving.

True locked knee

True locked knee occurs when something physically prevents the knee from straightening. When a person has true locked knee, their knee joint gets stuck in one position and cannot move at all.

The causes of locked knee vary depending on the type.

Causes of pseudo locked knee

Some potential causes of pseudo locked knee include:

  • pain from a knee injury
  • inflammation from injury or degenerative joint disease (osteoarthritis)
  • plica syndrome, which is inflammation of the knee joint tissue
  • patellar maltracking, where the kneecap does not move correctly

Causes of true locked knee

Some potential causes of true locked knee include:

Meniscal tear

The menisci are two pieces of ‘c’-shaped cartilage that sit either side of the knee joint. They act as a cushion between the bones of the shin and thigh.

If a meniscus tears, a fragment can break away and become stuck in the knee joint, causing the joint to lock.

A meniscal tear can occur during forceful twisting or rotation of the knee. Other causes include overuse and degenerative changes to the knee.

Loose bodies in the knee

Like cartilage, bone fragments can also embed themselves in the knee joint, causing it to lock.

Loose bodies such as cartilage and bone fragments can occur due to injury or osteoarthritis.

Patella dislocation

Certain injuries to the knee can cause the kneecap, or patella, to move out of position. This is called patella dislocation. It can cause the knee to lock during extension.

Knee joint inflammation

If the structures within the knee joint become swollen and inflamed, they may prevent extension of the knee. Swelling could occur as a result of injury, overuse, or osteoarthritis.

Symptoms of pseudo locked knee

The main symptom of pseudo locked knee is pain. A person may also experience the following symptoms:

  • a brief locking sensation in the knee
  • a sensation that the knee is catching
  • a feeling of looseness or instability in the knee

Symptoms of true locked knee

The primary symptom of true locked knee is the inability to straighten the knee. In some cases, a person with true locked knee may experience pain, as well.

If a loose body within a joint is causing true locked knee, a person might experience other signs and symptoms, including:

  • chronic stiffness in the knee
  • difficulty straightening the knee fully
  • popping sensation in the knee
  • feeling a bump at the site of the loose body
  • intermittent pain and swelling
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Imaging scans of the knee may help reveal the underlying cause of a locked knee.

A doctor will begin by asking questions about symptoms, such as pain and swelling. They will then physically examine the knee to check for signs of bruising, inflammation, and tenderness.

During the examination, the doctor may push or pull on the knee to evaluate the joint. They may then ask the person to walk across the room to assess their mobility.

Sometimes, a doctor may recommend diagnostic imaging to examine the knee more closely. Examples of such tests include:

  • magnetic resonance imaging (MRI)
  • computerized tomography (CT) scan
  • X-ray
  • ultrasound

Other tests can help the doctor to check for signs of inflammation or infection. These include blood tests, and a procedure called an arthrocentesis. This procedure involves taking a sample of fluid from the knee joint.

Treatments will vary based on the type of locked knee a person has and its underlying cause.

Meniscal tears

The treatment for a meniscal tear depends on its location and severity.

If the tear is small and in the outer part of the meniscus, the doctor may recommend following the RICE procedure. The acronym RICE stands for:

  • Rest: Stop doing the activity that causes pain
  • Ice: Apply a covered ice pack for 15–20 minutes at a time several times each day
  • Compression: Wear an elastic compression bandage
  • Elevation: Lay with knee higher than the heart. This helps to drain excess blood from the knee, reducing swelling.

Nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, can also help to alleviate pain and inflammation.

In some cases, a doctor may recommend physical therapy to help the person regain movement in the knee joint.

Loose body in the knee

If a person has a loose piece of cartilage or bone that is causing the knee to lock, they may require surgery to remove it.

Other causes

Other causes, such as patellar maltracking or plica syndrome, usually require physical therapy alongside ice, rest, and anti-inflammatory medications.

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A person may prevent injury by exercising within their physical limits.

It is not always possible to prevent the injuries and conditions that can cause locked knee.

However, there are measures people can take to help protect their knees. These include;

  • avoiding playing contact sports
  • taking a break from activities that cause knee pain
  • exercising within physical limits
  • strengthening the leg muscles and core
  • maintaining flexibility
  • taking caution on slippery or unstable areas to help avoid falls

There are two types of locked knee — true and pseudo. In true locked knee, the knee is physically incapable of moving. In pseudo locked knee, the knee is physically capable of moving, but the person cannot move it due to severe pain or swelling.

Both types of locked knee typically require pain medications, ice, and rest. A doctor may also recommend physical therapy to help restore movement in the knee joint. If these measures do not work, some form of surgery may be necessary.

A person who experiences locked knee should see their doctor as soon as possible for a diagnosis.