Plica syndrome is a condition that causes chronic knee pain. It happens when the plica, a fold or thick band of tissue in the synovial tissue that protects the knee, develops inflammation.

Plica syndrome can happen when someone suddenly falls or injures their knee. More often, it is a chronic condition due to overuse, repetitive injury, or repetitive motion.

A person can typically manage symptoms at home with a combination of stretches, physical therapy, and pain medication. However, more severe cases may require surgery.

Additionally, research involving knee surgery patients suggests that doctors may underdiagnose plica syndrome or confuse it with other causes of knee pain, such as osteoarthritis.

Read on to learn more about plica syndrome.

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Plicae are thick bands, or folds, of tissue within the knee joint. They can sometimes rub on the sides of the bones or surface cartilage, leading to symptoms of pain, inflammation, or irritation.

These folds do not serve any purpose in the body.

However, some people develop inflamed plicae, which doctors call plica syndrome. The condition causes pain in the knee and a popping or clicking sensation. Some individuals also have a sense of instability in the knee.

In most cases, plica syndrome pain gets worse when doing specific movements, such as squatting.

Doctors may advise whether a person will require surgery to improve their condition or whether conservative management is enough.

Who might it affect?

Not everyone has plicae, and doctors disagree about what causes them to develop.

When they develop, doctors are unsure why some plicae become inflamed in some people and not in others.

Children, adolescents, and adults can develop plica syndrome. Typically, people develop this condition before the age of 30 years.

When plicae become inflamed and cause symptoms, moving or supporting weight on the knee can be painful.

Additionally, people may have pain in one or more plicae:

  • Suprapatellar plica: The plica in the top of the knee.
  • Lateral plica: The plica toward the back of the knee.
  • Medial plica: The plica under the suprapatellar plica, toward the front of the knee — the most common source of plica syndrome.
  • Infrapatellar plica: The plica in the middle of the knee.

What other conditions can affect the knee?

Plica syndrome is not the only cause of knee pain. It is important to rule out other potential causes, such as:

The main symptom of plica syndrome is a pain in the knee, especially if it occurs when the knee pops, clicks, or makes other sounds.

Some other common symptoms include:

  • a noise in the knee
  • pain that is often but not always on the top of the knee
  • pain that worsens during weight-bearing activity, such as when squatting
  • a feeling of instability in the knee

Various studies report that 3 to 30% of people in the European population develop plica syndrome at some point, though many do not experience any symptoms.

Sometimes, injury or overuse causes plicae to become inflamed. This might happen if a person:

  • has a fall
  • experiences an athletic injury
  • repeatedly stresses their knees, such as when running or lifting heavy weights

No single test can conclusively diagnose plica syndrome.

Doctors use two exams to assess for plica syndrome:

  • Stutter test:
    1. A person sits on a table with their legs dangling off the edge at a 90-degree angle.
    2. A doctor places their fingers on the top of the knee while the individual extends their leg.
    3. If the doctor feels a shake or pop in the knee, the test is positive.
  • Hughston test:
    1. A person lies on their back while extending their painful knee.
    2. The doctor puts one hand on the heel and the other hand over the top of the knee.
    3. They then push the knee while rotating the leg inward and flexing and extending the knee.
    4. If the person experiences knee pain or there is popping, this test is positive.

A person might be positive on only one test and still have plica syndrome. If this occurs, a doctor may recommend imaging tests, such as an MRI or ultrasound.

However, imaging tests cannot detect every case of plica syndrome. Therefore, a doctor may rely primarily on symptoms and the results of a physical exam.

Conservative treatment is the first line of treatment and is often effective. These nonsurgical treatments may include:

  • Physical therapy: This helps improve function and reduce pain. It involves an exercise plan that does not intensify symptoms.
  • Medication: This helps manage pain in the knee and elsewhere.
  • Stretching and strength training: These programs aim to help strengthen the joint muscles, hamstrings, and quadriceps.
  • Corticosteroid injections: These injections help reduce inflammation and pain.
  • Activity modifications: These modifications reduce knee stress. They include walking instead of running or avoiding activities that place significant strain on the knee.

People with asymptomatic plica do not need treatment.

Surgical treatment involves a procedure known as arthroscopy, which can both diagnose and treat knee problems. During the procedure, a surgeon makes an incision into the knee and inserts a narrow tube called an arthroscope into the knee. A doctor can then locate and remove inflamed plicae.

Arthroscopy may also help with diagnosing other causes of knee pain.

Plica syndrome can respond well to conservative, nonsurgical treatment. Therefore, doctors usually only recommend this procedure if other treatments fail or the pain is severe enough to undermine a person’s daily functioning.

Following prompt treatment, a person’s outlook is typically positive. People with plica syndrome should adhere to any home exercise plans and advice from their doctor.

Working with a doctor and other specialists can help a person lay out the right treatment plan for them. This may or may not involve surgical interventions.

Plica syndrome ranges from minor, short-term pain to a chronic condition triggering severe pain and disability. Conservative treatments, such as exercise and stretching, often work. When they are ineffective, surgery may relieve symptoms.

People with knee pain can consult a doctor who specializes in knee pain and should ask about the possibility of plica syndrome if their knee clicks or pops.