Three bones meet within the knee joint: the femur, or thighbone, the tibia, or shinbone, and the patella, or kneecap. Surrounding each of these bones is articular cartilage, the smooth, spongy tissue that allows the bones to glide fluidly against one another. Osteochondritis is the gradual softening and degeneration of the articular cartilage in the knee, causing the cartilage to flake from off the bone. Since loose flakes of cartilage increase friction inside the joint and allow bones to scrape against one another, the condition can be quite painful. Osteochondritis Dissecans (OCD) can occur in both children and adults.
There is no universally accepted reason why OCD develops, nor are there specific risks to developing OCD. There may be an element of repeated trauma to the knee causing damage to the joint surface. Currently, this is only speculative.