Meniscal Cyst

A tear int he meniscus can lead to the formation of a meniscal cyst.. SPRINGER MEDIZIN / Getty Images

A meniscal cyst is an outpouching of joint fluid caused by a tear within the meniscus cartilage. Meniscal cysts are most commonly seen near the lateral meniscus (outside of the knee) and are associated with a specific type of meniscal tear called a horizontal cleavage tear.

Signs of a Meniscal Cyst

The most common sign of a meniscal cyst is pain directly over the joint line along with a bump or lump in that location.

  Sometimes the cyst will fluctuate in size, while others it will remain seemingly unchanged.

The reason the cyst form is that the tear in the meniscus cartilage allows normal joint fluid to leak out of the joint.  The body is constantly making new joint fluid and absorbing excess fluid  However, when the fluid escapes the joint, it can form a pouch called a meniscal cyst.  The reason the cyst stays, is that the tear can act as a one-way valve, where fluid can escape the joint into the cyst, but doesn't come back out the other way.

It is important to understand that while called a "cyst" it is really just a pouch of fluid and not a true cyst.  It is not an abnormal growth, it is not a tumor.  It is simply a collection of normal joint fluid that has escaped to an abnormal location.

Treatment Options

Meniscal cysts can be drained with a needle in the office, but they will often come back. The reason for the return of the meniscal cyst is that the tear that leads to the cyst must also be treated.

  Unless the underlying cause of the tear is addressed, the problem will usually return.

The meniscal cysts are usually best treated with arthroscopic treatment of the meniscal tear.  Once the tear has be addressed, the meniscal cyst will usually decompress and less commonly returns.  While it is possible for the cyst to come back, it is uncommon.

  Removing the actual cyst is not necessary; simply addressing the cause of the cyst is the better treatment for this problem.

Meniscal cysts are similar to popliteal or Baker's cysts--however, a popliteal cyst is located in the back of the knee joint.  In addition, a popliteal cyst is seen with many types of knee joint problems that lead to fluid accumulation or knee swelling.  Therefore, popliteal cysts can occur when there is a meniscus tear, but also with arthritis, ligament injuries, and other problems that lead to knee swelling.

Source:

Greis PE, et al. "Meniscal Injury: II. Management" J. Am. Acad. Ortho. Surg., May/June 2002; 10: 177 - 187.

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