This article is about OA rather than immune mediated forms of arthritis such as inflammatory or rheumatoid arthritis. OA is not a disease in and of itself, but is a degenerative condition caused by other joint problems. Normal cartilage is smooth and wear resistant, allowing nearly frictionless movement. The cartilage covers the end of the bone, called the subchondral bone. The synovial fluid cushions the bones of a joint, while ligaments enclose the joint capsule and provide stability.
Muscles provide additional support to the joint.
If a joint is damaged or is improperly constructed, changes will occur to the cartilage. The surface will become rough, stress to the underlying layers causes fissures, collagen breaks down, cartilage thins, proteoglycan is depleted or lost into the synovial fluid. The increase of pain causes the dog to exercise less, causing the surrounding muscle to atrophy which increases stress on an already painful joint. The dog limps, or bunny hops, shows reluctance to jump into the car or go up or down stairs, prefers to lie down rather than sit or stand, or any number of other behavioral or temperament changes. In order to minimize the chances of a dog's developing OA, the first and most important thing is the selection of a breeder.