The meniscus is a cartilage structure in the knee that sits on top of the leg bone (tibia). Each knee has two menisci, an inner and outer meniscus. The meniscus functions:
- Like an adaptor between the rounded thigh bone (femur) and flat tibia.
- Serves to help distribute the forces between the two bones over a greater area (rather than point to point.)
- Helps supply nutrition to the cartilage that lines the bones (articular cartilage).
- Helps stabilize the knee.
Each individual meniscus can be torn, especially as one gets older. A meniscal cyst is the result of a degenerative meniscal tear. A degenerative meniscal tear causes joint irritation that results in fluid being produced. The excess fluid can push out the joint capsule, causing a firm cyst through a one-way valve.
Frequent Signs and Symptoms
- Occasionally, a painless bump
- Pain, especially with standing on the affected leg, and tenderness along the joint of the knee
- Firm bump at the cyst, usually at the outer side of the knee; often more apparent when the knee is straight and may get smaller or disappear when the knee is bent
- Swelling within the knee
- Locking of the knee joint, causing inability to straighten the knee completely
- Giving way or buckling of the knee
Etiology (Causes)
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.