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I tore the meniscus in my left knee while playing soccer on wet grass. I felt a wrenching sensation but kept playing because there wasn't any swelling. I'm sure I reinjured it during the next game. Why didn't the knee swell up to warn me of an injury?

There are two menisci between the shinbone (tibia) and thighbone (femur) in the knee joint. (Menisci is plural for meniscus.) The C-shaped medial meniscus is on the inside part of the knee, closest to your other knee. (Medial means closer to the middle of the body.) The U-shaped lateral meniscus is on the outer half of the knee joint. (Lateral means further out from the center of the body.)

The meniscus is thin but has a wedge shape when viewed from the side. The outer edge of the meniscus is thicker than the central part. There's more blood supply to the outer edge. The inside or central part of the meniscus doesn't have a blood supply. It gets its nutrients from the synovial fluid inside the joint.

The thicker wedge of the medial meniscus is attached to the joint capsule and ligaments. The thinner central portion is free to move in and out slightly during normal knee motion. Both parts of the meniscus work to give the knee joint a smooth fit and easy movement. Both functions are needed for the kinds of loads the knee holds up under.

Without a lot of blood vessels, injury results in pain but doesn't cause swelling. A locking sensation or even "giving way" of the leg can occur when the meniscus is torn.

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