What is a meniscal cyst?
The meniscus is the cartilage pad that provides a number of functions to the knee’s health. It serves as a shock absorber, provides stress transmission, enhances lubrication and even facilitates nutrition. When the meniscus is torn, a small cyst can form adjacent to the meniscus tear. This cyst is thought to develop as part of the body’s healing response. The cyst is thought to develop by soft tissue surrounding the tear, which then develops a synovial lining with the secretion of synovial fluid into the cyst. In and of itself, a cyst is of little consequence and is present secondary to the meniscus tear. But sometimes the cyst itself causes discomfort and may be noticeable over the joint line where the meniscus is torn.
How does a meniscal cyst occur?
Meniscal cysts are usually seen with meniscal tears that occur with aging, although there may be an associated injury to the knee (pivoting or twisting injury). Kneeling or squatting may also cause tears of the meniscus. Given the number of meniscus tears, associated cysts are uncommon.
What increases the risk?
- Twisting, turning sports, in which the menisci can be sheared and 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) 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 meniscus tear and the associated cyst.
This condition should be distinguished from a “Baker’s cyst” which is not really a cyst but a collection of fluid that accumulates usually on the medial (inside) back of the knee. This “cyst” in fact represents an area where the knee joint synovial lining extends into the back of the knee but is usually “uninflated.” When the knee becomes swollen for any reason, fluid can expand this space and form a cyst. Most of the time the Baker’s cyst requires no treatment and is observed on an MRI.
Are there any special tests?
- MRI is the standard test to confirm the diagnosis and demonstrate its extent and location.
- Ultrasound can also demonstrate the cyst, and can be used to target aspiration (placing a needle into the lesion and drawing out the contents, usually a viscous, yellow, oily synovial fluid).
How is a meniscal cyst treated?
A meniscus cyst does not obligate surgical treatment. If incidental or minimally symptomatic, it may require nothing more than 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 will advocate instilling a small amount of cortisone into the cyst, though the merits of this approach are unproven. A meniscus cyst does not necessarily grow or change, and there is no overt reason one must have it operated upon.
Surgery is often 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 identified and surgically debrided, removing pathologic tissue using a motorized shaver to which suction has been attached. Because there is always a communication with the adjacent meniscus cyst, probing to identify and decompress the associated cyst is imperative. A shaver decompresses the cyst. Once the meniscus tear is cleaned up and the cyst is decompressed, the symptoms will resolve and the cyst will disappear.
What are the complications of treatment?
Possible complications of non-operative treatment include:
- Persistence or increase of cyst.
Possible complications of operative treatment include:
- Inadequate meniscectomy or cyst decompression, with residual cyst prominence and/or pain
- Loss of normal meniscus due to surgical excision, with subsequent risk of arthritis
- Surgical complications of arthroscopic surgery
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 participation in any sport. If surgery is performed to address the meniscus and decompress the cyst, return to activities can be as early as 3 weeks.
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.