The knees are some of the body’s most hardworking joints, bearing much of the body’s weight.

It’s very concerning if you can’t bend or straighten your legs. You might feel that your knee or knees have locked into place. This condition is aptly called a “locked knee.”

There are two types of knee locking: a true knee lock and a pseudo knee lock.

A true knee lock occurs when something in your knee joint gets stuck into one position and you cannot move it at all. The knee joint is designed to bend up and down and to rotate. When something blocks the movement of the knee, it might lock and not move. Sometimes this can be very painful.

True knee locking

True knee locking can be caused by:

A meniscus tear

The meniscus is a type of cartilage in your knee that looks like a bucket handle or the letter “C.” It acts as a cushion between your shinbone and thighbone. Meniscus tears are one of the most common types of knee injuries.

They can occur when you perform an activity where you forcefully twist or rotate your knee, especially when you have your full weight on it. Your knee can lock when the torn part of this cartilage gets in the way of your knee moving correctly. Besides knee locking, symptoms include:

  • a popping sensation
  • swelling
  • stiffness
  • pain, especially when trying to twist or rotate your knee
  • difficulty straightening your knee fully

A loose body

This occurs when a piece of your knee bone breaks off due to:

  • a fall
  • degenerative joint disease
  • chip fracture
  • torn cartilage
  • a foreign object from a past surgery
  • decreased blood supply or other trauma

The bone fragment will float around your knee joint. Your knee can lock if this loose body gets caught and stops your knee from moving normally. Other symptoms of a loose body include:

  • pain and swelling that comes and goes
  • feeling the loose body as a small bump or shard when you touch your knee, and possibly being able to move it with your fingers
  • chronic stiffness

Pseudo knee locking

If you have pseudo knee locking, you feel as though you can’t move your knee because you are in so much pain. However, there isn’t something in your knee actually preventing you from moving your leg.

This is your body causing a muscle spasm triggered by pain in or near your knee. The main symptom of pseudo knee locking is pain, accompanied by an inability to move the knee. Other symptoms include:

  • catching sensations
  • brief locking sensations
  • free or open sensations in the knee

Some causes for pseudo knee locking include:

Knee injury

This can be caused by:

  • a fracture
  • dislocation or subluxation, especially of the patella
  • bursitis
  • tendonitis
  • tendon tears

Inflammation and swelling

This is often caused by trauma to the knee or degenerative disease. Symptoms vary.

Plica syndrome

This condition causes an irritation of a fold in the knee joint tissue. Other symptoms include:

  • aching
  • swelling
  • pain that worsens when climbing stairs, squatting, or bending
  • a catching or locking sensation, especially when getting up from sitting
  • difficulty sitting for long periods of time
  • a clicking or cracking sound when you bend or extend your knee
  • a feeling that your knee is going to give out
  • feeling unstable on stairs and slopes
  • locking of the knee

Patellar maltracking

This is a condition that causes your kneecap to move incorrectly. Symptoms include:

  • pain at the front of the knee that occurs when ascending or descending, and while running
  • pain that occurs during or after prolonged periods of sitting
  • instability of the knee
  • locking of the knee

The treatment of your locked knee depends on its cause and the severity of the cause.

To treat a meniscus tear

A meniscus tear is the most common cause of a true knee lock. To treat a meniscus tear, your doctor will likely recommend rest, ice, and anti-inflammatory medication. They are also likely to recommend physical therapy to strengthen the muscles around your knee and in your legs, which will help stabilize your knee joint and reduce pain and locking.

If you keep having symptoms, and especially if locking continues, your doctor will probably recommend surgery. In children and young adults, meniscus tears can usually be repaired. However, in older people and in severe tears, surgical repair may not be possible. In this case, a surgeon will try to trim your meniscus to prevent it from getting caught in your knee.

After your surgery, you will need a period of rest for your knee to heal. Later, you’ll need to perform therapeutic exercises to boost your knee strength and stability.

To treat a loose body

Treatment of a loose body is fairly straightforward: surgery is needed to remove it. In some cases, additional surgery is needed to repair the kneecap if the loose body has caused damage.

You’ll need a rest period after your surgery to allow the tissues in your knee to heal.

To treat plica syndrome, patellar maltracking, and other causes

Other conditions are often best treated with a good physical therapy regimen. Your doctor will make such a recommendation for therapy after examining your knee(s). Rest, ice, and anti-inflammatory medications can also help alleviate the symptoms of a pseudo locked knee.

There are several possible causes of a locked knee, and each has its own treatment regimen. Treatments for a true locked knee and pseudo locked knee can be similar, and involve physical therapy, rest, ice, and anti-inflammatory medications.

However, some causes of a locked knee may require more intense treatments, such as surgery. The recovery periods tend to be longer for surgical treatments, meaning it might take you a long period of time to get back on your feet.

Building and maintaining muscle strength in the knee and in the leg muscles can help prevent the injuries and conditions that can lead to locked knee. Talk to your doctor about various preventative exercises you can do to help keep your knees healthy and strong.