Cartilage malformation/damage due to genetic predisposition traum and environmental factors, such as high plane of nutrition. Combined these factors lead to disruption of endochondral ossification which causes a thickening of the cartilage. The cartilage cells closest to the subchondral bone have decreased nutrition causing them to degenerate and fissures to form.  When a fissure reaches the joint surface, necrotic debris enters the joint, resulting in inflammation. This inflammation causes joint pain.  The fissure may encircle the thickened zone of cartilage, causing it to dislodge and become a joint mouse. The joint mice and chronic inflammation lead to degenerative joint disease.