Osteochondritis dissecans, commonly known as OCD and osteochondrosis dissecans, is a disease of the cartilage that affects the joints in a dog’s body. In any joint in the body two bones come together and movement is allowed between them. Where the two bones meet, an exceptionally smooth area of cartilage covers their surfaces. This acts as a cushion and protects the underlying bone. If anything disrupts this smooth cartilage surface, movement of the joint becomes painful. In a dog with OCD, this cartilage is damaged or grows abnormally. Instead of being attached to the bone it covers, it separates or cracks, causing great pain. In some cases, small pieces of cartilage break off and float free in the joint. These pieces of cartilage do not die, but rather continue to grow and increase in size. These are known as joint mice. Approximately 15% of all dogs will develop OCD. This article will cover the disease and its treatment and will explore some of the suspected causes.