Osteochondritis dissecans is a disease that affects a dog’s joints – at the shoulders, the elbows, the hips, the knees, and the ankles. When a dog has this condition, the cartilage of the joints gets inflamed and separates from the bone of the joints. The inflamed cartilage then continues growing, unattached from the bone, which causes a big buildup of thick, inflexible cartilage in the joint.