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).
Many different types of joint injuries and joint disorders can lead to chondromalacia. In the knee, chondromalacia is usually related to injury, overuse of the knee, and poorly aligned muscles and bones around the knee joint. These causes include:
Trauma, especially a fracture (break) or dislocation of the kneecap
An imbalance of the muscles around the knee (Some muscles are weaker than others.)
Overuse (repeated bending or twisting) of the knee joint, especially during sports
Poorly aligned muscles or bones near the knee joint
Injury to a meniscus (C-shaped cartilage inside the knee joint)
Rheumatoid arthritis or osteoarthritis
An infection in the knee joint
Repeated episodes of bleeding inside the knee joint
Repeated injections of steroid drugs into the knee
Chondromalacia of the knee affects young adults more than any other age group. It is especially common in runners, joggers, skiers, soccer players, cyclists and other athletes who repeatedly stress their knees. Also, workers who spend a lot of time kneeling – particularly carpet layers, tile setters and floor layers – are more likely to develop this problem.