Joints are complex structures. They are made up of bones, cartilage, tendons, ligaments and the joint capsule. The cartilage at the surface of the bone tip allows the bones to move along each other without causing pain.

Osteoarthritis occurs when the joint cartilage becomes damaged. This can happen after any overloading of the joint, such as sprains or tendon strain. But if the ligaments of the joint are stretched, the horse is in a different position or if the joints are loose, damage may occur sooner. The joint can also be damaged by cracks in the bone or cartilage. Often the talent, construction and heredity of the horse also play an important role.

The more and the heavier the work a horse does, the heavier the joints will be loaded.