An Overview of Meniscal Cysts

The meniscus cartilage is the joint pad inside the knee. A meniscal cyst is a collection of joint fluid caused by a tear within the meniscus cartilage. Joint fluid is also called synovial fluid.

Some people with meniscal cysts do not have any symptoms. Others may have pain, swelling, or problems moving the knee.

This article looks at meniscal cysts and their symptoms, causes, diagnosis and treatment.

Symptoms of a Meniscal Cyst

Meniscal cysts do not always cause symptoms. When they do, the most common are:

• Pain in the knee when standing
• Tenderness directly along the joint
• A bump or lump at the cyst site, usually near the outside of the knee
• A bump that becomes more visible as the knee straightens, though the bump itself may be painless
• A bump that changes size (though it may also remain seemingly unchanged)
• Swelling or locking of the knee joint

What Causes a Meniscal Cyst?

Meniscal cysts are most common in 20- to 30-year-old males. They are usually associated with a type of meniscal tear called a horizontal cleavage tear.

This kind of tear may be caused by over-rotation of the knee. It can also be caused by direct impact to the front or side of the knee. Disproportionate force on the knees, such as when you run on an uneven surface, can also cause this type of injury.

Cysts may also be caused by degeneration of the meniscus. This is usually related to age or osteoarthritis.

A tear in the meniscus allows joint fluid to leak out of the joint. This is what causes the cyst.

A meniscal cyst is not a true cyst. Instead, it is made up of displaced joint fluid. When fluid escapes the joint, it can collect in a pouch. This pouch is the cyst.

The cartilage tear can act as a one-way valve. Fluid can escape the joint into the cyst, but it can't go back into the joint. Because of this, the cyst will continue to collect fluid.

Risk factors for meniscal cysts include:

• Knee injury or meniscal injury
• Participation in contact sports or any sport where there is twisting of the knee joint, like football, soccer, rugby, or tennis
• Increasing age or osteoarthritis
• Ligament injuries, such as a torn anterior cruciate ligament (ACL)

Diagnosis of Meniscal Cysts

A healthcare provider will ask you questions about:

• Knee pain
• Popping sounds
• Recent injuries or impact to the knee

This will help determine if you have a meniscal tear. A meniscal cyst can usually be palpated, which means a doctor can feel it.

Range of motion tests can confirm there are no torn pieces of cartilage in the joint.

There are a few tests doctors use to assess meniscal tears and other knee injuries. These include:

• The McMurray test
• The Apley test
• The Stienmann I test
• The Payr's test
• Childress' sign
• The Ege's test

These are motion, weight-bearing, and pressure tests that can help doctors identify a tear. They can also help a doctor decide if the tear needs surgery.

Diagnosis may be confirmed by a magnetic resonance imaging (MRI) scan or ultrasound.

An MRI is a test that creates images of your knee using a magnetic field and radio waves. An ultrasound creates images using sound waves.

These tests will help your doctor see both the cyst and the tear.

Meniscal Cysts vs. Baker's Cysts

Meniscal cysts are similar to popliteal or Baker's cysts. Baker's cysts, however, are located in the back of the knee joint. 

Baker's cysts are seen with many types of knee joint problems that lead to fluid accumulation. They can occur with meniscus tears, but also with arthritis, ligament injuries, and other problems that cause knee swelling.

Treatment of Meniscal Cysts

Pain caused by a meniscal cyst can be treated with ice. Anti-inflammatory medications can also help.

The cyst may be drained with a needle in a doctor's office. Unfortunately, the cyst will usually return unless the meniscal tear is treated or heals itself.

Surgery

Meniscal tears don't always need surgery. When they do, the most common surgery is a minimally invasive arthroscopic surgical approach. This is where a surgeon uses instruments passed through small incisions to operate on the joint.

Once the tear has been repaired, the cyst will usually go away. While it is possible for the cyst to come back, it is unlikely.

Summary

Meniscal cysts don't always cause symptoms. When they do, symptoms may include pain, a bump on the knee, and swelling or locking of the joint.

Meniscal cysts are caused by tears in the meniscal cartilage. This can happen after injury or because of degeneration of the meniscus.

A meniscal cyst is a pouch of joint fluid that drains from the joint. A doctor may be able to feel it, and the diagnosis can be confirmed through a number of different tests. 

Meniscal cysts can be drained, but the best treatment is to repair the tear.

A Word From Verywell

Though it is called a cyst, a meniscal cyst is really just a pouch of dislocated joint fluid. It is not a growth or a tumor. It is simply a collection of normal joint fluid in an abnormal location.

If you don't have pain, you may resume normal activities right away. If you do feel some pain, swelling, or locking of the knee, your doctor can help you find the right treatment.