The joints in your body are cushioned with a type of tissue called articular cartilage. This tough, rubbery tissue covers the ends of bones inside a joint. As the joint moves, the cartilage helps to cushion the bones and allows them to glide smoothly against one another.
Sometimes, the cartilage inside a joint softens and breaks down. This condition is called chondromalacia. The cartilage loses its ability to protect the ends of the bones as the joint moves. The ends of the bones can rub together, causing pain.
Chondromalacia can affect any joint, but the most common location is inside the knee. It usually begins as a small area of softened cartilage behind the kneecap (patella) that can be painful. Eventually, more of the cartilage softens, and the softened cartilage can crack or shred into a mass of fibers. In severe cases, the damaged cartilage can wear away completely, down to the undersurface of the kneecap. If this happens, the exposed kneecap's bony surface can grind painfully against other knee bones. Also, bits of cartilage can float inside the joint, further irritating the cells that line the joint. In response, these cells produce fluid inside the joint (called a joint effusion).
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