What is a meniscal cyst?

The meniscus is a cartilage pad that serves as a shock absorber, provides stress transmission, enhances lubrication and facilitates nutrition to the knee. When the meniscus is torn, a small cyst can form adjacent to the tear. This cyst is thought to develop as part of the body’s healing response. Alone, a cyst is of little consequence and is present only secondary to the meniscus tear. However, the cyst itself can discomfort and may be noticeable over the joint line where the meniscus is torn.

How does a meniscal cyst occur?

Meniscal cysts are often seen with meniscal tears that occur due to degenerative changes within the meniscus, although there may be an associated injury to the knee (pivoting or twisting injury). Given the frequency of meniscus tears, associated cysts are uncommon.

What increases the risk?

• Twisting, turning sports, in which the menisci can be torn
• Previous knee injury
• Associated knee injury, particularly ligament injuries
• Age, in which degenerative meniscus tears increase in frequency

What are the symptoms of a meniscal cyst?

• Pain, especially when standing on the affected leg, and tenderness along the joint of the knee
• Firm bump at the site of the cyst, more commonly over the lateral (outside) aspect of the knee
• Cyst may become more apparent as knee is extended
• Occasionally, a painless bump
• Associated non-specific findings may include knee swelling, joint line tenderness over the affected meniscus, “locking” of the joint or ligament injury.

How is a meniscal cyst diagnosed?

Diagnosis is usually readily apparent by inspection and palpation of a discrete mass directly over a tender medial or lateral joint line. Diagnosis is confirmed by MRI, which shows both the cyst and the associated meniscus tear. This condition should not be confused with a “Baker’s cyst”, which is a collection of fluid that most commonly accumulates on the medial (inside) back of the knee. When the knee becomes swollen for any reason, fluid can expand this space and form a cyst.

Are any special tests used to diagnose a meniscal cyst?

• MRI can confirm the diagnosis and establish the size and location of the cyst

• Ultrasound can also help to visualize the cyst, and guide aspiration, in which a needle is placed into the cyst to draw out its contents

How is a meniscal cyst treated?

If incidental or minimally symptomatic, treatment may require occasional icing and/or anti-inflammatory medicine. The cyst may be aspirated using local anesthetic and a small needle to remove the cysts’ contents. However, this is usually only temporarily effective, and the fluid returns. Some physicians may advocate instilling a small amount of cortisone into the cyst.

Surgery may be recommended as definitive treatment. This is accomplished by arthroscopy, in which a small camera is introduced into the knee joint, and another small portal (opening) is made to permit instruments to be brought into the joint. During arthroscopy, the torn meniscus is surgically debrided (removed). The associated meniscal cyst will then be decompressed.

When can you return to your sport or activity?

Although meniscus cysts do not “heal,” they may become asymptomatic over time, particularly with activity modification. If the cyst is not symptomatic, there is no reason one cannot participate in activities. If surgery is performed to address the meniscus and decompress the cyst, the patient may be able to return to activity as early at 3 weeks post-operatively.

How can a meniscal cyst be prevented?

There is no established means by which cysts can be specifically prevented. Maintaining good fitness and conditioning can preclude injury to a vulnerable knee. Athletes should wear proper protective equipment and ensure correct fit, including the proper length cleats for the surface.